147-497: Flu is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae, the influenza viruses. Flu or FLU may also refer to: Flu Influenza , commonly known as the flu , is an infectious disease caused by influenza viruses . Symptoms range from mild to severe and often include fever , runny nose , sore throat , muscle pain , headache , coughing , and fatigue . These symptoms begin one to four (typically two) days after exposure to
294-477: A dry cough , sore or dry throat , hoarse voice , and a stuffy or runny nose . Coughing is the most common symptom. Gastrointestinal symptoms may also occur, including nausea, vomiting, diarrhea, and gastroenteritis, especially in children. The standard influenza symptoms typically last for two to eight days. Some studies suggest influenza can cause long-lasting symptoms in a similar way to long COVID . Symptomatic infections are usually mild and limited to
441-458: A runny nose . The time between exposure to the virus and development of symptoms (the incubation period ) is one to four days, most commonly one to two days. Many infections are asymptomatic. The onset of symptoms is sudden, and initial symptoms are predominately non-specific, including fever, chills, headaches, muscle pain , malaise , loss of appetite , lack of energy, and confusion. These are usually accompanied by respiratory symptoms such as
588-570: A 5 August 2011 PLOS ONE article, researchers estimated that the 2009 H1N1 global infection rate was 11% to 21%, lower than what was previously expected. However, by 2012, research showed that as many as 579,000 people could have been killed by the disease, as only those fatalities confirmed by laboratory testing were included in the original number, and meant that many without access to health facilities went uncounted. The majority of these deaths occurred in Africa and Southeast Asia. Experts, including
735-401: A case fatality rate of 2–3%. By 14 November 2009, the virus had infected one in six Americans with 200,000 hospitalisations and 10,000 deaths—as many hospitalizations and fewer deaths than in an average flu season overall, but with much higher risk for those under 50. With deaths of 1,100 children and 7,500 adults 18 to 64, these figures were deemed "much higher than in a usual flu season" during
882-519: A certain strain in childhood still possess antibodies to that strain at a reasonable level later in life, which can provide some protection to related strains. There is, however, an " original antigenic sin ", in which the first HA subtype a person is exposed to influences the antibody-based immune response to future infections and vaccines. Annual vaccination is the primary and most effective way to prevent influenza and influenza-associated complications, especially for high-risk groups. Vaccines against
1029-901: A culture of mammalian cells or embryonated eggs for 3–10 days to monitor cytopathic effect. Final confirmation can then be done via antibody staining, hemadsorption using red blood cells , or immunofluorescence microscopy. Shell vial cultures, which can identify infection via immunostaining before a cytopathic effect appears, are more sensitive than traditional cultures with results in 1–3 days. Cultures can be used to characterize novel viruses, observe sensitivity to antiviral drugs, and monitor antigenic drift, but they are relatively slow and require specialized skills and equipment. Serological assays can be used to detect an antibody response to influenza after natural infection or vaccination. Common serological assays include hemagglutination inhibition assays that detect HA-specific antibodies, virus neutralization assays that check whether antibodies have neutralized
1176-461: A distinct "head" and "stalk" structure. M2 proteins form proton channels through the viral envelope that are required for viral entry and exit. Influenza B viruses contain a surface protein named NB that is anchored in the envelope, but its function is unknown. The viral life cycle begins by binding to a target cell. Binding is mediated by the viral HA proteins on the surface of the envelope, which bind to cells that contain sialic acid receptors on
1323-741: A heavier toll among chronically ill children than the seasonal flu usually does". Through 8 August 2009, the CDC had received 36 reports of pediatric deaths with associated influenza symptoms and laboratory-confirmed pandemic H1N1 from state and local health authorities within the United States, with 22 of these children having neurodevelopmental conditions such as cerebral palsy , muscular dystrophy , or developmental delays . "Children with nerve and muscle problems may be at especially high risk for complications because they cannot cough hard enough to clear their airways". From 26 April 2009, to 13 February 2010,
1470-425: A hemagglutinin-esterase fusion (HEF) protein on one segment that merges the functions of HA and NA. The final genome segment encodes the viral nucleoprotein (NP). Influenza viruses also encode various accessory proteins, such as PB1-F2 and PA-X, that are expressed through alternative open reading frames and which are important in host defense suppression, virulence, and pathogenicity. The virus particle, called
1617-598: A high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma , and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia , but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with
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#17328520326611764-401: A higher risk of developing complications if these individuals are still shedding the virus. Antiviral treatment is also recommended if a person is hospitalized with suspected influenza instead of waiting for test results to return and if symptoms are worsening. Most antiviral drugs against influenza fall into two categories: neuraminidase (NA) inhibitors and M2 inhibitors. Baloxavir marboxil is
1911-609: A higher temperature than mammalian influenza viruses. Newly synthesized viral polymerase subunits and NP proteins are imported to the nucleus to further increase the rate of viral replication and form RNPs. HA, NA, and M2 proteins are trafficked with the aid of M1 and NEP proteins to the cell membrane through the Golgi apparatus and inserted into the cell's membrane. Viral non-structural proteins including NS1, PB1-F2, and PA-X regulate host cellular processes to disable antiviral responses. PB1-F2 also interacts with PB1 to keep polymerases in
2058-542: A limited number, so it is difficult to predict when the next will happen. The Global Influenza Surveillance and Response System of the World Health Organization (GISRS) tests several millions of specimens annually to monitor the spread and evolution of influenza viruses. People who are infected can transmit influenza viruses through breathing, talking, coughing, and sneezing, which spread respiratory droplets and aerosols that contain virus particles into
2205-414: A major focus of research pertaining to antiviral drugs, vaccines, and other measures against influenza. Influenza C virus is subclassified into six genetic/antigenic lineages. Influenza D virus has been isolated from pigs and cattle, the latter being the natural reservoir. Infection has also been observed in humans, horses, dromedary camels, and small ruminants such as goats and sheep. Influenza D virus
2352-430: A national emergency, giving Secretary of Health and Human Services Kathleen Sebelius authority to grant waivers to requesting hospitals from usual federal requirements. By 19 November 2009, doses of vaccine had been administered in over 16 countries. A 2009 review by the U.S. National Institutes of Health (NIH) concluded that the 2009 H1N1 vaccine has a safety profile similar to that of the seasonal vaccine. In 2011,
2499-488: A notable exception, which targets the endonuclease activity of the viral RNA polymerase and can be used as an alternative to NA and M2 inhibitors for influenza A virus and influenza B virus. 2009 swine flu pandemic The 2009 swine flu pandemic , caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving
2646-450: A pandemic. Influenza C virus, like influenza B virus, is primarily found in humans, though it has been detected in pigs, feral dogs, dromedary camels, cattle, and dogs. Influenza C virus infection primarily affects children and is usually asymptomatic or has mild cold-like symptoms, though more severe symptoms such as gastroenteritis and pneumonia can occur. Unlike influenza A virus and influenza B virus, influenza C virus has not been
2793-449: A period of improvement in symptoms for one to three weeks followed by recurrent fever, sputum production, and fluid buildup in the lungs , but can also occur just a few days after influenza symptoms appear. About a third of primary pneumonia cases are followed by secondary pneumonia, which is most frequently caused by the bacteria Streptococcus pneumoniae and Staphylococcus aureus . Influenza viruses comprise four species, each
2940-501: A review of the WHO's actions, spokeswoman Fadela Chaib stated: "Criticism is part of an outbreak cycle. We expect and indeed welcome criticism and the chance to discuss it". The WHO also stated on their website that "The world is going through a real pandemic. The description of it as a fake is wrong and irresponsible". In March 2010, the Council of Europe launched an enquiry into "the influence of
3087-795: A room for people developing flu-like symptoms while they waited to go home and to have ill students or staff and those caring for them use face masks. In California, school districts and universities were on alert and worked with health officials to launch education campaigns. Many planned to stockpile medical supplies and discuss worst-case scenarios, including plans to provide lessons and meals for low-income children in case elementary and secondary schools closed. University of California campuses stockpiled supplies, from paper masks and hand sanitizer to food and water. To help prepare for contingencies, University of Maryland School of Medicine professor of pediatrics James C. King Jr. suggested that every county should create an "influenza action team" to be run by
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#17328520326613234-523: A secondary bacterial pneumonia . A November 2009 New England Journal of Medicine article recommended that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics . In particular, it is a warning sign if a child seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia. Some studies estimated that the real number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of
3381-424: A secondary bacterial infection occurs, then antibiotics may be necessary. Antiviral drugs are primarily used to treat severely ill patients, especially those with compromised immune systems. Antivirals are most effective when started in the first 48 hours after symptoms appear. Later administration may still be beneficial for those who have underlying immune defects, those with more severe symptoms, or those who have
3528-463: A severe outcome, as were radiologically confirmed pneumonia and a raised C-reactive protein (CRP) level (≥ 100 mg/L) . 59% of all in-hospital deaths occurred in previously healthy people. Fulminant (sudden-onset) myocarditis has been linked to infection with H1N1, with at least four cases of myocarditis confirmed in patients also infected with A/H1N1. Three out of the four cases of H1N1-associated myocarditis were classified as fulminant, and one of
3675-532: A simple way of obtaining assay results, are low cost, and produce results in less than 30 minutes, so they are commonly used, but they can not distinguish between influenza A virus and influenza B virus or between influenza A virus subtypes and are not as sensitive as nucleic-acid based tests. Nucleic acid-based tests (NATs) amplify and detect viral nucleic acid. Most of these tests take a few hours, but rapid molecular assays are as fast as RIDTs. Among NATs, reverse transcription polymerase chain reaction (RT-PCR)
3822-602: A study from the US Flu Vaccine Effectiveness Network estimated the overall effectiveness of all pandemic H1N1 vaccines at 56%. A CDC study released 28 January 2013, estimated that the Pandemic H1N1 vaccine saved roughly 300 lives and prevented about a million illnesses in the US. The study concluded that had the vaccination program started two weeks earlier, close to 60% more cases could have been prevented. The study
3969-527: A surface or object—with flu viruses on it and then touching their face. The basic reproduction number (the average number of other individuals whom each infected individual will infect, in a population which has no immunity to the disease) for the 2009 novel H1N1 is estimated to be 1.75. A December 2009 study found that the transmissibility of the H1N1 influenza virus in households is lower than that seen in past pandemics. Most transmissions occur soon before or after
4116-570: A test for pandemic H1N1 flu specifically, because the test results usually do not affect the recommended course of treatment. The U.S. CDC recommend testing only for people who are hospitalized with suspected flu, pregnant women, and people with weakened immune systems. For the mere diagnosis of influenza and not pandemic H1N1 flu specifically, more widely available tests include rapid influenza diagnostic tests (RIDT), which yield results in about 30 minutes, and direct and indirect immunofluorescence assays ( DFA and IFA), which take 2–4 hours. Due to
4263-448: A transcriptase, PB2, which recognizes 5' caps , and PA (P3 for influenza C virus and influenza D virus), an endonuclease . The M1 matrix protein and M2 proton channel share a segment, as do the non-structural protein (NS1) and the nuclear export protein (NEP). For influenza A virus and influenza B virus, hemagglutinin (HA) and neuraminidase (NA) are encoded on one segment each, whereas influenza C virus and influenza D virus encode
4410-476: A type of white blood cell, produce antibodies that bind to influenza antigens HA and NA (or HEF ) and other proteins to a lesser degree. Once bound to these proteins, antibodies block virions from binding to cellular receptors, neutralizing the virus. In humans, a sizeable antibody response occurs about one week after viral exposure. This antibody response is typically robust and long-lasting, especially for influenza C virus and influenza D virus. People exposed to
4557-550: A type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. Almost all possible combinations of H (1 thru 16) and N (1 thru 11) have been isolated from wild birds. In addition H17, H18, N10 and N11 have been found in bats. The influenza A virus subtypes in circulation among humans as of 2018 are H1N1 and H3N2. Influenza B virus mainly infects humans but has been identified in seals, horses, dogs, and pigs. Influenza B virus does not have subtypes like influenza A virus but has two antigenically distinct lineages, termed
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4704-514: A very small region of central Mexico. Initially called an "outbreak", widespread H1N1 infection was first recognized in the state of Veracruz , Mexico, with evidence that the virus had been present for months before it was officially called an "epidemic". The Mexican government closed most of Mexico City 's public and private facilities in an attempt to contain the spread of the virus; however, it continued to spread globally, and clinics in some areas were overwhelmed by infected people. The new virus
4851-464: A video for employers to use as they developed plans to respond to the H1N1 outbreak. The guidance suggested that employers consider and communicate their objectives, such as reducing transmission among staff, protecting people who are at increased risk of influenza-related complications from becoming infected, maintaining business operations, and minimising adverse effects on other entities in their supply chains . The CDC estimated that as much as 40% of
4998-425: A virion, is pleomorphic and varies between being filamentous, bacilliform, or spherical in shape. Clinical isolates tend to be pleomorphic, whereas strains adapted to laboratory growth typically produce spherical virions. Filamentous virions are about 250 nanometers (nm) by 80 nm, bacilliform 120–250 by 95 nm, and spherical 120 nm in diameter. The core of the virion comprises one copy of each segment of
5145-400: A year, once for each hemisphere, to discuss which strains should be included based on observation from HA inhibition assays. Other manufacturing methods include an MDCK cell culture-based inactivated vaccine and a recombinant subunit vaccine manufactured from baculovirus overexpression in insect cells. Influenza can be prevented or reduced in severity by post-exposure prophylaxis with
5292-465: Is a sudden, drastic change in an influenza virus' antigen, usually HA. During antigenic shift, antigenically different strains that infect the same cell can reassort genome segments with each other, producing hybrid progeny. Since all influenza viruses have segmented genomes, all are capable of reassortment. Antigenic shift only occurs among influenza viruses of the same genus and most commonly occurs among influenza A viruses. In particular, reassortment
5439-465: Is acidified by cellular vATPase to have lower pH, which triggers a conformational change in HA that allows fusion of the viral envelope with the endosomal membrane. At the same time, hydrogen ions diffuse into the virion through M2 ion channels, disrupting internal protein-protein interactions to release RNPs into the host cell's cytosol . The M1 protein shell surrounding RNPs is degraded, fully uncoating RNPs in
5586-763: Is characterized by high levels of viral replication in the lower respiratory tract, accompanied by a strong pro-inflammatory response called a cytokine storm . Infection with H5N1 or H7N9 especially produces high levels of pro-inflammatory cytokines. In bacterial infections, early depletion of macrophages during influenza creates a favorable environment in the lungs for bacterial growth since these white blood cells are important in responding to bacterial infection. Host mechanisms to encourage tissue repair may inadvertently allow bacterial infection. Infection also induces production of systemic glucocorticoids that can reduce inflammation to preserve tissue integrity but allow increased bacterial growth. The pathophysiology of influenza
5733-419: Is dependent on vaccination with biosecurity. Diagnosis based on symptoms is fairly accurate in otherwise healthy people during seasonal epidemics and should be suspected in cases of pneumonia, acute respiratory distress syndrome (ARDS), sepsis , or if encephalitis, myocarditis , or breakdown of muscle tissue occur. Because influenza is similar to other viral respiratory tract illnesses, laboratory diagnosis
5880-436: Is diagnosed with laboratory methods such as antibody or antigen tests and a polymerase chain reaction ( PCR ) to identify viral nucleic acid . The disease can be treated with supportive measures and, in severe cases, with antiviral drugs such as oseltamivir . In healthy individuals, influenza is typically self-limiting and rarely fatal, but it can be deadly in high-risk groups. In a typical year, five to 15 percent of
6027-477: Is distantly related to influenza C virus. While cattle workers have occasionally tested positive to prior influenza D virus infection, it is not known to cause disease in humans. Influenza C virus and influenza D virus experience a slower rate of antigenic evolution than influenza A virus and influenza B virus. Because of this antigenic stability, relatively few novel lineages emerge. Every year, millions of influenza virus samples are analysed to monitor changes in
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6174-425: Is exported out of the nucleus and translated by host ribosomes in a cap-dependent manner to synthesize viral proteins. RdRp also synthesizes complementary positive-sense strands of the viral genome in a complementary RNP complex which are then used as templates by viral polymerases to synthesize copies of the negative-sense genome. During these processes, RdRps of avian influenza viruses (AIVs) function optimally at
6321-541: Is extremely interesting because it demonstrates for the first time what we had worried about at the very onset of the pandemic, and that is that this particular virus, when introduced into pigs, could reassort with the resident viruses in pigs and we would have new gene constellations. And bingo, here we are." Pigs have been termed the mixing vessel of flu because they can be infected both by avian flu viruses, which rarely directly infect people, and by human viruses. When pigs become simultaneously infected with more than one virus,
6468-532: Is hard to bend these criteria, no matter what the motive". On 7 May 2009, the WHO stated that containment was not feasible and that countries should focus on mitigating the effect of the virus. They did not recommend closing borders or restricting travel. On 26 April 2009, the Chinese government announced that visitors returning from flu-affected areas who experienced flu-like symptoms within two weeks would be quarantined. U.S. airlines had made no major changes as of
6615-427: Is in the area about two meters around an infected person via respiratory droplets that come into contact with mucosa of the upper respiratory tract. Transmission through contact with a person, bodily fluids, or intermediate objects ( fomites ) can also occur, since influenza viruses can survive for hours on non-porous surfaces. If one's hands are contaminated, then touching one's face can cause infection. Influenza
6762-506: Is intracellular and performed by ubiquitous proteases, which allows for infection of a greater variety of cells, thereby contributing to more severe disease. Cells possess sensors to detect viral RNA, which can then induce interferon production. Interferons mediate expression of antiviral proteins and proteins that recruit immune cells to the infection site, and they notify nearby uninfected cells of infection. Some infected cells release pro-inflammatory cytokines that recruit immune cells to
6909-511: Is longer. In the UK, the Health and Safety Executive (HSE) also issued general guidance for employers. The U.S. CDC did not recommend the use of face masks or respirators in non-health care settings, such as schools, workplaces, or public places, with a few exceptions: people who were ill with the virus when around other people, and people who were at risk for severe illness while caring for someone with
7056-630: Is more common in children. Staphylococcus aureus , including methicillin-resistant strains, is an important cause of secondary bacterial pneumonia with a high mortality rate; Streptococcus pneumoniae is the second most important cause of secondary bacterial pneumonia for children and primary for adults. Neuromuscular and cardiac complications are unusual but may occur. A United Kingdom investigation of risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza looked at 631 patients from 55 hospitals admitted with confirmed infection from May through September 2009. 13% were admitted to
7203-614: Is necessary for confirmation. Common sample collection methods for testing include nasal and throat swabs. Samples may be taken from the lower respiratory tract if infection has cleared the upper but not lower respiratory tract. Influenza testing is recommended for anyone hospitalized with symptoms resembling influenza during flu season or who is connected to an influenza case. For severe cases, earlier diagnosis improves patient outcome. Diagnostic methods that can identify influenza include viral cultures , antibody- and antigen-detecting tests, and nucleic acid-based tests. Viruses can be grown in
7350-734: Is not known to cause illness. In humans, influenza viruses are primarily transmitted through respiratory droplets from coughing and sneezing. Transmission through aerosols and surfaces contaminated by the virus also occur. Frequent hand washing and covering one's mouth and nose when coughing and sneezing reduce transmission, as does wearing a mask. Annual vaccination can help to provide protection against influenza. Influenza viruses, particularly influenza A virus, evolve quickly, so flu vaccines are updated regularly to match which influenza strains are in circulation. Vaccines provide protection against influenza A virus subtypes H1N1 and H3N2 and one or two influenza B virus subtypes. Influenza infection
7497-595: Is rapid, with many patients progressing to respiratory failure within 24 hours, requiring immediate admission to an intensive care unit . Upon admission, most patients need immediate respiratory support with mechanical ventilation . Most complications have occurred among previously unhealthy individuals, with obesity and respiratory disease as the strongest risk factors. Pulmonary complications are common. Primary influenza pneumonia occurs most commonly in adults and may progress rapidly to acute lung injury requiring mechanical ventilation . Secondary bacterial infection
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#17328520326617644-544: Is recommended for people who have yet to receive a vaccine for the current flu season, who have been vaccinated less than two week since contact, if there is a significant mismatch between vaccine and circulating strains, or during an outbreak in a closed setting regardless of vaccination history. These are the main ways that influenza spreads When vaccines and antiviral medications are limited, non-pharmaceutical interventions are essential to reduce transmission and spread. The lack of controlled studies and rigorous evidence of
7791-413: Is recommended to avoid alcohol and tobacco use while ill. Aspirin is not recommended to treat influenza in children due to an elevated risk of developing Reye syndrome . Corticosteroids are not recommended except when treating septic shock or an underlying medical condition, such as chronic obstructive pulmonary disease or asthma exacerbation, since they are associated with increased mortality. If
7938-764: Is removed and facilities are disinfected and "no carry-over" policies to eliminate infectious material before new poultry arrive can be used to reduce the spread of influenza viruses. If a novel influenza viruses has breached the aforementioned biosecurity measures, then rapid detection to stamp it out via quarantining, decontamination, and culling may be necessary to prevent the virus from becoming endemic. Vaccines exist for avian H5, H7, and H9 subtypes that are used in some countries. In China, for example, vaccination of domestic birds against H7N9 successfully limited its spread, indicating that vaccination may be an effective strategy if used in combination with other measures to limit transmission. In pigs and horses, management of influenza
8085-464: Is significantly influenced by which receptors influenza viruses bind to during entry into cells. Mammalian influenza viruses preferentially bind to sialic acids connected to the rest of the oligosaccharide by an α-2,6 link, most commonly found in various respiratory cells, such as respiratory and retinal epithelial cells. AIVs prefer sialic acids with an α-2,3 linkage, which are most common in birds in gastrointestinal epithelial cells and in humans in
8232-566: Is simpler. Examples are B/Santiago/29615/2020 and C/Minnesota/10/2015. Influenza viruses have a negative-sense , single-stranded RNA genome that is segmented. The negative sense of the genome means it can be used as a template to synthesize messenger RNA (mRNA). Influenza A virus and influenza B virus have eight genome segments that encode 10 major proteins. Influenza C virus and influenza D virus have seven genome segments that encode nine major proteins. Three segments encode three subunits of an RNA-dependent RNA polymerase (RdRp) complex: PB1,
8379-516: Is slower in B than A and slowest in C and D. Antigenic drift is a major cause of seasonal influenza, and requires that flu vaccines be updated annually. HA is the main component of inactivated vaccines, so surveillance monitors antigenic drift of this antigen among circulating strains. Antigenic evolution of influenza viruses of humans appears to be faster than in swine and equines. In wild birds, within-subtype antigenic variation appears to be limited but has been observed in poultry. Antigenic shift
8526-461: Is the most traditional and considered the gold standard for diagnosing influenza because it is fast and can subtype influenza A virus, but it is relatively expensive and more prone to false-positives than cultures. Other NATs that have been used include loop-mediated isothermal amplification -based assays, simple amplification-based assays, and nucleic acid sequence-based amplification. Nucleic acid sequencing methods can identify infection by obtaining
8673-407: Is usually transmissible from one day before the onset of symptoms to 5–7 days after. In healthy adults, the virus is shed for up to 3–5 days. In children and the immunocompromised, the virus may be transmissible for several weeks. Children ages 2–17 are considered to be the primary and most efficient spreaders of influenza. Children who have not had multiple prior exposures to influenza viruses shed
8820-497: Is very common in AIVs, creating a large diversity of influenza viruses in birds, but is uncommon in human, equine, and canine lineages. Pigs, bats, and quails have receptors for both mammalian and avian influenza A viruses, so they are potential "mixing vessels" for reassortment. If an animal strain reassorts with a human strain, then a novel strain can emerge that is capable of human-to-human transmission. This has caused pandemics, but only
8967-519: Is when an influenza virus' antigens change due to the gradual accumulation of mutations in the antigen's (HA or NA) gene. This can occur in response to evolutionary pressure exerted by the host immune response. Antigenic drift is especially common for the HA protein, in which just a few amino acid changes in the head region can constitute antigenic drift. The result is the production of novel strains that can evade pre-existing antibody-mediated immunity. Antigenic drift occurs in all influenza species but
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#17328520326619114-500: The Loyola University Health System, who suggests that rapid tests may actually pose a dangerous public health risk. Nikki Shindo of the WHO has expressed regret at reports of treatment being delayed by waiting for H1N1 test results and suggests, "[D]octors should not wait for the laboratory confirmation but make diagnosis based on clinical and epidemiological backgrounds and start treatment early." On 22 June 2010,
9261-558: The US Centers for Disease Control and Prevention (USCDC) and Netherlands Institute for Health Services Research (NIVEL) to produce two independent estimates of the influenza deaths that occurred during the global pandemic using two distinct methodologies. The 2009 H1N1 flu pandemic is estimated to have actually caused about 284,000 (range from 150,000 to 575,000) excess deaths by the WHO-USCDC study and 148,000–249,000 excess respiratory deaths by
9408-471: The upper respiratory tract , but progression to pneumonia is relatively common. Pneumonia may be caused by the primary viral infection or a secondary bacterial infection . Primary pneumonia is characterized by rapid progression of fever, cough, labored breathing , and low oxygen levels that cause bluish skin . It is especially common among those who have an underlying cardiovascular disease such as rheumatic heart disease . Secondary pneumonia typically has
9555-555: The 2009 H1N1 outbreak was not an effective method of infection control. U.S. government officials were especially concerned about schools because the H1N1 flu virus appeared to disproportionately affect young and school-age people, between six months and 24 years of age. The H1N1 outbreak led to numerous precautionary school closures in some areas. Rather than closing schools, the CDC recommended that students and school workers with flu symptoms should stay home for either seven days total, or until 24 hours after symptoms subsided, whichever
9702-553: The B/Victoria/2/1987-like and B/Yamagata/16/1988-like lineages, or simply (B/)Victoria(-like) and (B/)Yamagata(-like). Both lineages are in circulation in humans, disproportionately affecting children. However, the B/Yamagata lineage might have become extinct in 2020/2021 due to COVID-19 pandemic measures. Influenza B viruses contribute to seasonal epidemics alongside influenza A viruses but have never been associated with
9849-547: The CDC announced a new test called the "CDC Influenza 2009 A (H1N1)pdm Real-Time RT-PCR Panel (IVD)". It uses a molecular biology technique to detect influenza A viruses and specifically the 2009 H1N1 virus. The new test will replace the previous real-time RT-PCR diagnostic test used during the 2009 H1N1 pandemic, which received an emergency use authorization from the U.S. Food and Drug Administration in April 2009. Tests results are available in four hours and are 96% accurate. The virus
9996-576: The CDC had received reports of the deaths of 277 children with laboratory-confirmed 2009 influenza A (H1N1) within the United States. The World Health Organization reports that the clinical picture in severe cases is strikingly different from the disease pattern seen during epidemics of seasonal influenza. While people with certain underlying medical conditions are known to be at increased risk, many severe cases occur in previously healthy people. In severe cases, patients generally begin to deteriorate around three to five days after symptom onset. Deterioration
10143-463: The CDC's Advisory Committee on Immunization Practices voted for "universal" flu vaccination in the U.S. to include all people over six months of age. The 2010–2011 vaccine will protect against the 2009 H1N1 pandemic virus and two other flu viruses. On 27 April 2009, the European Union health commissioner advised Europeans to postpone nonessential travel to the United States or Mexico. This followed
10290-456: The H1N1 strain is "unquestionably higher". Critics claimed the WHO had exaggerated the danger, spreading "fear and confusion" rather than "immediate information". The WHO began an investigation to determine whether it had "frightened people unnecessarily". A flu follow-up study done in September 2010, found that "the risk of most serious complications was not elevated in adults or children." In
10437-478: The H1N1 swine flu strain were hospitalised within 30 days, compared with 3.7% of those sick with a seasonal strain of H1N1 and 3.1% with an H3N2 virus. Confirmed diagnosis of pandemic H1N1 flu requires testing of a nasopharyngeal , nasal, or oropharyngeal tissue swab from the patient. Real-time RT-PCR is the recommended test as others are unable to differentiate between pandemic H1N1 and regular seasonal flu . However, most people with flu symptoms do not need
10584-508: The H1N1 virus (the first being the 1918–1920 Spanish flu pandemic and the second being the 1977 Russian flu ). The first identified human case was in La Gloria , Mexico, a rural town in Veracruz. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to
10731-546: The UK, the NHS recommended vaccine priority go to people over six months old who were clinically at risk for seasonal flu, pregnant women and households of people with compromised immunity. Although it was initially thought that two injections would be required, clinical trials showed that the new vaccine protected adults "with only one dose instead of two;" thus the limited vaccine supplies would go twice as far as had been predicted. Health officials worldwide were also concerned because
10878-607: The WHO and the U.S. CDC stopped counting cases and declared the outbreak a pandemic . Despite being informally called "swine flu", the H1N1 flu virus cannot be spread by eating pork products; similar to other influenza viruses, it is typically contracted by person to person transmission through respiratory droplets. Symptoms usually last 4–6 days. Antivirals ( oseltamivir or zanamivir ) were recommended for those with more severe symptoms or those in an at-risk group. The pandemic began to taper off in November 2009, and by May 2010,
11025-605: The WHO's "false pandemic" flu campaign is "one of the greatest medicine scandals of the century". He said that the "false pandemic" campaign began in May 2009 in Mexico City , when a hundred or so "normal" reported influenza cases were declared to be the beginning of a threatening new pandemic, although he said there was little scientific evidence for it. Nevertheless, he argued that the WHO, "in cooperation with some big pharmaceutical companies and their scientists, re-defined pandemics," removing
11172-630: The WHO, have agreed that an estimated 284,500 people were killed by the disease, much higher than the initial death toll. The symptoms of H1N1 flu are similar to those of other influenzas , and may include fever, cough (typically a "dry cough"), headache, dizziness, sneezing, muscle or joint pain, sore throat , chills , fatigue , and runny nose . Diarrhea , vomiting, and neurological problems have also been reported in some cases. People at higher risk of serious complications include people over 65, children younger than 5, children with neurodevelopmental conditions , pregnant women (especially during
11319-462: The WHO, replied stating, "Without question, the BMJ feature and editorial will leave many readers with the impression that WHO's decision to declare a pandemic was at least partially influenced by a desire to boost the profits of the pharmaceutical industry. The bottom line, however, is that decisions to raise the level of pandemic alert were based on clearly defined virological and epidemiological criteria. It
11466-487: The WHO-NIVEL study. A study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly seasonal flu . For comparison, the WHO estimates that 250,000 to 500,000 people die of seasonal flu annually. However, the H1N1 influenza epidemic in 2009 resulted in a large increase in the number of new cases of narcolepsy . The World Health Organization uses
11613-409: The air. A person susceptible to infection can contract influenza by coming into contact with these particles. Respiratory droplets are relatively large and travel less than two meters before falling onto nearby surfaces. Aerosols are smaller and remain suspended in the air longer, so they take longer to settle and can travel further. Inhalation of aerosols can lead to infection, but most transmission
11760-465: The airways, loss of alveolar structure, loss of lung epithelial integrity due to epithelial cell infection and death, and degradation of the extracellular matrix that maintains lung structure. In particular, alveolar cell infection appears to drive severe symptoms since this results in impaired gas exchange and enables viruses to infect endothelial cells, which produce large quantities of pro-inflammatory cytokines . Pneumonia caused by influenza viruses
11907-463: The antiviral drugs oseltamivir , which can be taken orally by those at least three months old, and zanamivir , which can be inhaled by those above seven years. Chemoprophylaxis is most useful for individuals at high risk for complications and those who cannot receive the flu vaccine. Post-exposure chemoprophylaxis is only recommended if oseltamivir is taken within 48 hours of contact with a confirmed or suspected case and zanamivir within 36 hours. It
12054-808: The beginning of June 2009, but continued standing practices which include looking for passengers with symptoms of flu, measles or other infections, and relying on in-flight air filters to ensure that aircraft were sanitised. Masks were not generally provided by airlines and the CDC did not recommend that airline crews wear them. Some non-U.S. airlines, mostly Asian, including Singapore Airlines , China Eastern Airlines , China Southern Airlines , Cathay Pacific and Aeromexico , took measures such as stepping up cabin cleaning, installing state-of-the-art air filters and allowing in-flight staff to wear face masks. According to studies conducted in Australia and Japan, screening individuals for influenza symptoms at airports during
12201-427: The cytoplasmic side of the membrane. The viral genome is incorporated inside a viral envelope derived from portions of the cell membrane that have HA, NA, and M2 proteins. At the end of budding, HA proteins remain attached to cellular sialic acid until they are cleaved by the sialidase activity of NA proteins. The virion is then released from the cell. The sialidase activity of NA also cleaves any sialic acid residues from
12348-404: The cytosol. RNPs are then imported into the nucleus with the help of viral localization signals. There, the viral RNA polymerase transcribes mRNA using the genomic negative-sense strand as a template. The polymerase snatches 5' caps for viral mRNA from cellular RNA to prime mRNA synthesis and the 3'-end of mRNA is polyadenylated at the end of transcription. Once viral mRNA is transcribed, it
12495-709: The discovery of the first confirmed case in Spain. On 6 May 2009, the Public Health Agency of Canada announced that their National Microbiology Laboratory (NML) had mapped the genetic code of the swine flu virus, the first time that had been done. In the U.K., the National Health Service launched a website, the National Pandemic Flu Service, allowing patients to self-assess and get an authorisation number for antiviral medication. The system
12642-530: The effectiveness of some measures has hampered planning decisions and recommendations. Nevertheless, strategies endorsed by experts for all phases of flu outbreaks include hand and respiratory hygiene, self-isolation by symptomatic individuals and the use of face masks by them and their caregivers, surface disinfection, rapid testing and diagnosis, and contact tracing . In some cases, other forms of social distancing including school closures and travel restrictions are recommended. Reasonably effective ways to reduce
12789-462: The flu are trivalent or quadrivalent, providing protection against an H1N1 strain, an H3N2 strain, and one or two influenza B virus strains corresponding to the two influenza B virus lineages. Two types of vaccines are in use: inactivated vaccines that contain "killed" (i.e. inactivated) viruses and live attenuated influenza vaccines (LAIVs) that contain weakened viruses. There are three types of inactivated vaccines: whole virus, split virus, in which
12936-443: The flu. There was some disagreement about the value of wearing face masks, as some experts feared that masks may have given people a false sense of security and should not have replaced other standard precautions. Yukihiro Nishiyama, professor of virology at Nagoya University 's School of Medicine, commented that the masks are "better than nothing, but it's hard to completely block out an airborne virus since it can easily slip through
13083-638: The frequent use of term "Mexican flu" in the news media. Official entities adopted terms with varying consistency over the course of the pandemic. The CDC used names like "novel influenza A (H1N1)" or "2009 H1N1 flu". The Netherlands National Institute for Public Health and the Environment used the term "Pig Flu" early on. Officials in Taiwan suggested use of the names "H1N1 flu" or "new flu". The World Organization for Animal Health , an IGO based in Europe, proposed
13230-587: The gaps". According to mask manufacturer 3M , masks will filter out particles in industrial settings, but "there are no established exposure limits for biological agents such as swine flu virus". However, despite the lack of evidence of effectiveness, the use of such masks is common in Asia. They are particularly popular in Japan, where cleanliness and hygiene are highly valued and where etiquette obligates those who are sick to wear masks to avoid spreading disease. During
13377-537: The genome bound to NP nucleoproteins in separate ribonucleoprotein (RNP) complexes for each segment. There is a copy of the RdRp, all subunits included, bound to each RNP. The genetic material is encapsulated by a layer of M1 matrix protein which provides structural reinforcement to the outer layer, the viral envelope . The envelope comprises a lipid bilayer membrane incorporating HA and NA (or HEF ) proteins extending outward from its exterior surface. HA and HEF proteins have
13524-492: The global population of 6.8 billion at the time. The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic. However, the Spanish flu infected approximately a third of the world population at the time, a much higher proportion. The number of lab-confirmed deaths reported to the WHO is 18,449 and is widely considered a gross underestimate. The WHO collaborated with
13671-599: The height of the fear of a pandemic, some countries initiated or threatened to initiate quarantines of foreign visitors suspected of having or being in contact with others who may have been infected. In May 2009, the Chinese government confined 21 U.S. students and three teachers to their hotel rooms. As a result, the US State Department issued a travel alert about China's anti-flu measures and warned travellers against travelling to China if ill. In Hong Kong, an entire hotel
13818-548: The high rate of RIDT false negatives , the CDC advises that patients with illnesses compatible with novel influenza A (H1N1) virus infection but with negative RIDT results should be treated empirically based on the level of clinical suspicion, underlying medical conditions, severity of illness, and risk for complications, and if a more definitive determination of infection with influenza virus is required, testing with rRT-PCR or virus isolation should be performed. The use of RIDTs has been questioned by researcher Paul Schreckenberger of
13965-511: The immunity found in the older U.S. population. Analyses of the genetic sequences of the first isolates, promptly shared on the GISAID database according to Nature and WHO, soon determined that the strain contains genes from five different flu viruses: North American swine influenza, North American avian influenza, human influenza, and two swine influenza viruses typically found in Asia and Europe. Further analysis has shown that several proteins of
14112-446: The importance of pork and domestic pigs . As terminology changed to deal with these and other such issues, further criticism was made that the situation was unnecessarily confusing. For example, the news department at the journal Science produced an article with the humorous title "Swine Flu Names Evolving Faster Than Swine Flu Itself". Analysis of the genetic divergence of the virus in samples from different cases indicated that
14259-641: The late 1800s, pandemic outbreaks of novel influenza strains have occurred every 10 to 50 years. Five flu pandemics have occurred since 1900: the Spanish flu from 1918 to 1920, which was the most severe; the Asian flu in 1957; the Hong Kong flu in 1968; the Russian flu in 1977; and the swine flu pandemic in 2009. The symptoms of influenza are similar to those of a cold, although usually more severe and less likely to include
14406-522: The local health department , parents, and school administrators. By 28 October 2009, about 600 schools in the United States had been temporarily closed, affecting over 126,000 students in 19 states. Fearing a worst-case scenario, the U.S. Department of Health and Human Services (HHS), the Centers for Disease Control and Prevention and the Department of Homeland Security (DHS) developed updated guidance and
14553-471: The logistics of transporting, storing, and administering vaccines to be donated to poorer countries. In January 2010, Wolfgang Wodarg , a German deputy who trained as a physician and chaired the health committee at the Council of Europe , claimed that major firms had organized a "campaign of panic" to put pressure on the World Health Organization (WHO) to declare a "false pandemic" to sell vaccines. Wodarg said
14700-400: The lower respiratory tract. Cleavage of the HA protein into HA 1 , the binding subunit, and HA 2 , the fusion subunit, is performed by different proteases, affecting which cells can be infected. For mammalian influenza viruses and low pathogenic AIVs, cleavage is extracellular, which limits infection to cells that have the appropriate proteases, whereas for highly pathogenic AIVs, cleavage
14847-574: The name "North American influenza". The European Commission adopted the term "novel flu virus". Officials in Israel and South Korea briefly considered adoption of the name "Mexican virus" due to concern about the use of the word "swine". In Israel, objections stemmed from sensitivity to religious restrictions on eating pork in the Jewish and Muslim populations, in South Korea , concerns were influenced by
14994-510: The new strain, adults aged 18 to 60 had 6–9%, and older adults 33%. While it has been thought that these findings suggest the partial immunity in older adults may be due to previous exposure to similar seasonal influenza viruses, a November 2009 study of a rural unvaccinated population in China found only a 0.3% cross-reactive antibody reaction to the H1N1 strain, suggesting that previous vaccinations for seasonal flu and not exposure may have resulted in
15141-520: The nucleic acid sequence of viral samples to identify the virus and antiviral drug resistance. The traditional method is Sanger sequencing , but it has been largely replaced by next-generation methods that have greater sequencing speed and throughput. Treatment in cases of mild or moderate illness is supportive and includes anti-fever medications such as acetaminophen and ibuprofen , adequate fluid intake to avoid dehydration, and rest. Cough drops and throat sprays may be beneficial for sore throat. It
15288-414: The nucleus longer. M1 and NEP proteins localize to the nucleus during the later stages of infection, bind to viral RNPs and mediate their export to the cytoplasm where they migrate to the cell membrane with the aid of recycled endosomes and are bundled into the segments of the genome. Progeny viruses leave the cell by budding from the cell membrane, which is initiated by the accumulation of M1 proteins at
15435-519: The number of cases was in steep decline. On 10 August 2010, the Director-General of the WHO, Margaret Chan , announced the end of the H1N1 pandemic and announced that the H1N1 influenza event had moved into the post-pandemic period. According to WHO statistics (as of July 2010), the virus had killed more than 18,000 people since it appeared in April 2009; however, they state that the total mortality (including deaths unconfirmed or unreported) from
15582-460: The onset of symptoms. The H1N1 virus has been transmitted to animals, including swine , turkeys , ferrets , household cats, at least one dog, and a cheetah . Because the H1N1 vaccine was initially in short supply in the U.S., the CDC recommended that initial doses should go to priority groups such as pregnant women, people who live with or care for babies under six months old, children six months to four years old and health-care workers. In
15729-565: The organization to conduct a review of WHO's handling of the H1N1 flu pandemic. She told them, "We want a frank, critical, transparent, credible and independent review of our performance." In June 2010, Fiona Godlee , editor-in-chief of the BMJ , published an editorial which criticised the WHO, saying that an investigation had disclosed that some of the experts advising WHO on the pandemic had financial ties with drug companies which were producing antivirals and vaccines. Margaret Chan, Director-General of
15876-414: The pandemic. In June 2010, scientists from Hong Kong reported discovery of a new swine flu virus: a hybrid of the pandemic H1N1 virus and viruses previously found in pigs. It was the first report of a reassortment of the pandemic virus, which in humans had been slow to evolve. Nancy Cox , head of the influenza division at the U.S. Centers for Disease Control and Prevention, has said, "This particular paper
16023-613: The patients died. Also, there appears to be a link between severe A/H1N1 influenza infection and pulmonary embolism . In one report, five out of 14 patients admitted to the intensive care unit with severe A/H1N1 infection were found to have pulmonary emboli. An article published in JAMA in September 2010 challenged previous reports and stated that children infected in the 2009 flu pandemic were no more likely to be hospitalised with complications or get pneumonia than those who catch seasonal strains. Researchers found that about 1.5% of children with
16170-530: The pharmaceutical companies on the global swine flu campaign", and a preliminary report was in preparation. On 12 April 2010, Keiji Fukuda, the WHO's top influenza expert, stated that the system leading to the declaration of a pandemic led to confusion about H1N1 circulating around the world and he expressed concern that there was a failure to communicate in regard to uncertainties about the new virus, which turned out to be not as deadly as feared. WHO Director-General Margaret Chan appointed 29 flu experts from outside
16317-418: The population contracts influenza. There are 3 to 5 million severe cases annually, with up to 650,000 respiratory-related deaths globally each year. Deaths most commonly occur in high-risk groups, including young children, the elderly, and people with chronic health conditions. In temperate regions , the number of influenza cases peaks during winter, whereas in the tropics , influenza can occur year-round. Since
16464-695: The primary measures used. Placing poultry houses and piggeries on high ground away from high-density farms, backyard farms, live poultry markets, and bodies of water helps to minimize contact with wild birds. Closure of live poultry markets appears to the most effective measure and has shown to be effective at controlling the spread of H5N1, H7N9, and H9N2 . Other biosecurity measures include cleaning and disinfecting facilities and vehicles, banning visits to poultry farms, not bringing birds intended for slaughter back to farms, changing clothes, disinfecting foot baths, and treating food and water. If live poultry markets are not closed, then "clean days" when unsold poultry
16611-420: The primary reservoir of influenza A virus, especially aquatic birds such as ducks, geese, shorebirds, and gulls, but the virus also circulates among mammals, including pigs, horses, and marine mammals. Subtypes of Influenza A are defined by the combination of the antigenic viral proteins haemagglutinin (H) and neuraminidase (N) in the viral envelope ; for example, " H1N1 " designates an IAV subtype that has
16758-462: The primary source of influenza A virus (IAV), which is also widespread in various mammals, including humans and pigs. Influenza B virus (IBV) and influenza C virus (ICV) primarily infect humans, and influenza D virus (IDV) is found in cattle and pigs. Influenza A virus and influenza B virus circulate in humans and cause seasonal epidemics , and influenza C virus causes a mild infection, primarily in children. Influenza D virus can infect humans but
16905-400: The probability of reassortment. In general, influenza vaccines are only effective if there is an antigenic match between vaccine strains and circulating strains. Most commercially available flu vaccines are manufactured by propagation of influenza viruses in embryonated chicken eggs, taking 6–8 months. Flu seasons are different in the northern and southern hemisphere, so the WHO meets twice
17052-454: The public. It was argued that the names were overly technical (e.g. "H1N1"), incorrectly implying that the disease is caused by contact with pigs or pig products, or provoking stigmatization against certain communities (e.g. "Mexican"). Some academics of the time asserted there is nothing wrong with such names, while research published years later (in 2013) concluded that Mexican Americans and Latino Americans had indeed been stigmatized due to
17199-402: The result of lung inflammation and compromise caused by epithelial cell infection and death, combined with inflammation caused by the immune system's response to infection. Non-respiratory organs can become involved, but the mechanisms by which influenza is involved in these cases are unknown. Severe respiratory illness can be caused by multiple, non-exclusive mechanisms, including obstruction of
17346-507: The sanitizing effect lasts for longer. In hospitals, quaternary ammonium compounds and bleach are used to sanitize rooms or equipment that have been occupied by people with influenza symptoms. At home, this can be done effectively with a diluted chlorine bleach. Since influenza viruses circulate in animals such as birds and pigs, prevention of transmission from these animals is important. Water treatment , indoor raising of animals, quarantining sick animals, vaccination, and biosecurity are
17493-458: The sick, there is mixed evidence on beneficial effects in the community. Smoking raises the risk of contracting influenza, as well as producing more severe disease symptoms. Since influenza spreads through both aerosols and contact with contaminated surfaces, surface sanitizing may help prevent some infections. Alcohol is an effective sanitizer against influenza viruses, while quaternary ammonium compounds can be used with alcohol so that
17640-492: The site of infection. Immune cells control viral infection by killing infected cells and phagocytizing viral particles and apoptotic cells. An exacerbated immune response can harm the host organism through a cytokine storm. To counter the immune response, influenza viruses encode various non-structural proteins, including NS1, NEP, PB1-F2, and PA-X, that are involved in curtailing the host immune response by suppressing interferon production and host gene expression. B cells ,
17787-428: The sole member of its own genus. The four influenza genera comprise four of the seven genera in the family Orthomyxoviridae . They are: Influenza A virus is responsible for most cases of severe illness as well as seasonal epidemics and occasional pandemics. It infects people of all ages but tends to disproportionately cause severe illness in the elderly, the very young, and those with chronic health issues. Birds are
17934-408: The statement that "an enormous amount of people have contracted the illness or died" from its existing definition and replacing it by stating simply that there has to be a virus, spreading beyond borders and to which people have no immunity. The WHO responded by stating that they take their duty to provide independent advice seriously and guarded against interference from outside interests. Announcing
18081-456: The summer lull to take stock of the United States response to H1N1 flu and attempt to patch any gaps in the public health safety net before flu season started in early autumn. Preparations included planning a second influenza vaccination program in addition to the one for seasonal flu, and improving coordination between federal, state, and local governments and private health providers. On 24 October 2009, U.S. President Obama declared swine flu
18228-411: The sun, and crowding. Influenza viruses that infect the upper respiratory tract like H1N1 tend to be more mild but more transmissible, whereas those that infect the lower respiratory tract like H5N1 tend to cause more severe illness but are less contagious. In humans, influenza viruses first cause infection by infecting epithelial cells in the respiratory tract. Illness during infection is primarily
18375-472: The surface of the cell membrane. For N1 subtypes with the "G147R" mutation and N2 subtypes, the NA protein can initiate entry. Prior to binding, NA proteins promote access to target cells by degrading mucus, which helps to remove extracellular decoy receptors that would impede access to target cells. After binding, the virus is internalized into the cell by an endosome that contains the virion inside it. The endosome
18522-565: The term " swine flu ". Unlike most strains of influenza, the pandemic H1N1/09 virus did not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic . Even in the case of previously healthy people, a small percentage develop pneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs three to six days after initial onset of flu symptoms. The pneumonia caused by flu can be either direct viral pneumonia or
18669-434: The term "(H1N1) 2009 pandemic" when referring to the event, and officially adopted the name "A(H1N1)pdm09" for the virus in 2010, after the conclusion of the pandemic. Controversy arose early on regarding the wide assortment of terms used by journalists, academics, and officials. Labels like "H1N1 flu", "Swine flu", "Mexican flu", and variations thereof were typical. Criticism centered on how these names may confuse or mislead
18816-471: The third trimester), and people of any age with underlying medical conditions, such as asthma, diabetes, obesity, heart disease, or a weakened immune system (e.g., taking immunosuppressive medications or infected with HIV). More than 70% of hospitalizations in the U.S. have been people with such underlying conditions, according to the CDC . In September 2009, the CDC reported that the H1N1 flu "seems to be taking
18963-438: The transmission of influenza include good personal health and hygiene habits such as: not touching the eyes, nose or mouth; frequent hand washing (with soap and water, or with alcohol-based hand rubs); covering coughs and sneezes with a tissue or sleeve; avoiding close contact with sick people; and staying home when sick. Avoiding spitting is also recommended. Although face masks might help prevent transmission when caring for
19110-536: The viral surface, which helps prevent newly assembled viruses from aggregating near the cell surface and improving infectivity. Similar to other aspects of influenza replication, optimal NA activity is temperature- and pH-dependent. Ultimately, presence of large quantities of viral RNA in the cell triggers apoptosis (programmed cell death), which is initiated by cellular factors to restrict viral replication. Two key processes that influenza viruses evolve through are antigenic drift and antigenic shift . Antigenic drift
19257-477: The virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection . Other complications include acute respiratory distress syndrome , meningitis , encephalitis , and worsening of pre-existing health problems such as asthma and cardiovascular disease . There are four types of influenza virus: types A, B, C, and D. Aquatic birds are
19404-420: The virus are most similar to strains that cause mild symptoms in humans, leading virologist Wendy Barclay to suggest on 1 May 2009, that the initial indications are that the virus was unlikely to cause severe symptoms for most people. The virus was less lethal than previous pandemic strains and killed about 0.01–0.03% of those infected; the 1918 influenza was about one hundred times more lethal and had
19551-461: The virus at greater quantities and for a longer duration than other children. People at risk of exposure to influenza include health care workers, social care workers, and those who live with or care for people vulnerable to influenza. In long-term care facilities, the flu can spread rapidly. A variety of factors likely encourage influenza transmission, including lower temperature, lower absolute and relative humidity , less ultraviolet radiation from
19698-613: The virus is disrupted by a detergent, and subunit, which only contains the viral antigens HA and NA. Most flu vaccines are inactivated and administered via intramuscular injection. LAIVs are sprayed into the nasal cavity. Vaccination recommendations vary by country. Some recommend vaccination for all people above a certain age, such as 6 months, whereas other countries limit recommendations to high-risk groups. Young infants cannot receive flu vaccines for safety reasons, but they can inherit passive immunity from their mother if vaccinated during pregnancy. Influenza vaccination helps to reduce
19845-400: The virus jumped to humans in 2008, probably after June, and not later than the end of November, likely around September 2008. The research also indicated the virus had been latent in pigs for several months prior to the outbreak, suggesting a need to increase agricultural surveillance to prevent future outbreaks. In 2009, U.S. agricultural officials speculated, although emphasizing that there
19992-582: The virus was new and could easily mutate and become more virulent, even though most flu symptoms were mild and lasted only a few days without treatment. Officials also urged communities, businesses, and individuals to make contingency plans for possible school closures, multiple employee absences for illness, surges of patients in hospitals, and other effects of potentially widespread outbreaks. Disaster response organizations such as Direct Relief helped by providing protective items to clinical workers to help them stay healthy throughout flu season. In February 2010,
20139-481: The virus' antigenic properties, and to inform the development of vaccines. To unambiguously describe a specific isolate of virus, researchers use the internationally accepted influenza virus nomenclature, which describes, among other things, the species of animal from which the virus was isolated, and the place and year of collection. As an example – A/chicken/Nakorn-Patom/Thailand/CU-K2/04(H5N1) : The nomenclature for influenza B, C and D, which are less variable,
20286-560: The virus, and enzyme-linked immunoabsorbant assays. These methods tend to be relatively inexpensive and fast but are less reliable than nucleic-acid based tests. Direct fluorescent or immunofluorescent antibody (DFA/IFA) tests involve staining respiratory epithelial cells in samples with fluorescently-labeled influenza-specific antibodies, followed by examination under a fluorescent microscope. They can differentiate between influenza A virus and influenza B virus but can not subtype influenza A virus. Rapid influenza diagnostic tests (RIDTs) are
20433-561: The viruses can swap genes, producing new variants which can pass to humans and sometimes spread amongst them. "Unlike the situation with birds and humans, we have a situation with pigs and humans where there's a two-way street of exchange of viruses. With pigs it's very much a two-way street." Spread of the H1N1 virus is thought to occur in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing by people with influenza. Sometimes people may become infected by touching something—such as
20580-447: The workforce might be unable to work at the peak of the pandemic due to the need for many healthy adults to stay home and care for an ill family member, and advised that individuals should have steps in place should a workplace close down or a situation arise that requires remote work . The CDC further advised that persons in the workplace should stay home sick for seven days after getting the flu, or 24 hours after symptoms end, whichever
20727-523: Was based on an effectiveness in preventing cases, hospitalizations, and deaths of 62% for all subgroups except people over 65, for whom the effectiveness was estimated at 43%. The effectiveness was based on European and Asian studies and expert opinion. The delay in vaccine administration demonstrated the shortcomings of the world's capacity for vaccine-production, as well as problems with international distribution. Some manufacturers and wealthy countries had concerns regarding liability and regulations, as well as
20874-449: Was expected to reduce the burden on general practitioners . U.S. officials observed that six years of concern about H5N1 avian flu did much to prepare for the current H1N1 outbreak, noting that after H5N1 emerged in Asia, ultimately killing about 60% of the few hundred people infected over the years, many countries took steps to try to prevent any similar crisis from spreading further. The CDC and other U.S. governmental agencies used
21021-607: Was first isolated in late April by American and Canadian laboratories from samples taken from people with flu in Mexico, Southern California, and Texas. Soon the earliest known human case was traced to a case from 9 March 2009 in a 5-year-old boy in La Gloria, Mexico, a rural town in Veracruz. In late April, the World Health Organization (WHO) declared its first ever "public health emergency of international concern", or PHEIC , and in June,
21168-414: Was found to be a novel strain of influenza for which existing vaccines against seasonal flu provided little protection. A study at the U.S. Centers for Disease Control and Prevention published in May 2009 found that children had no preexisting immunity to the new strain but that adults, particularly those older than 60, had some degree of immunity . Children showed no cross-reactive antibody reaction to
21315-454: Was longer. The CDC also recommended that colleges should consider suspending fall 2009 classes if the virus began to cause severe illness in a significantly larger share of students than the previous spring. They also urged schools to suspend rules, such as penalties for late papers or missed classes or requirements for a doctor's note, to enforce "self-isolation" and prevent students from venturing out while ill; schools were advised to set aside
21462-459: Was no way to prove their hypothesis, that "contrary to the popular assumption that the new swine flu pandemic arose on factory farms in Mexico, [the virus] most likely emerged in pigs in Asia, but then traveled to North America in a human." However, a subsequent report by researchers at the Mount Sinai School of Medicine in 2016 found that the 2009 H1N1 virus likely originated from pigs in
21609-402: Was quarantined with 240 guests; Australia ordered a cruise ship with 2,000 passengers to stay at sea because of a swine flu threat. Egyptian Muslims who went on the annual pilgrimage to Mecca risked being quarantined upon their return. Russia and Taiwan said they would quarantine visitors with fevers who come from areas where the flu was present. Japan quarantined 47 airline passengers in
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