The Trinidad Regional Virus Laboratory (T.R.V.L.) was established in Port of Spain , in 1953 by the Rockefeller Foundation in co-operation with the Government of Trinidad and Tobago . It was originally housed in an old wooden army barracks near the docks in Port of Spain. A large wired-in "animal house" was built out back to house the many wild animals brought in for study.
126-559: The Virus lab's first Director was the renowned epidemiologist , Dr Wilbur Downs who served in that role until 1961. In that year the laboratory was moved to new buildings at Federation Park , Port of Spain and, in 1964, became part of the Department of Microbiology of the University of the West Indies under the direction of Dr Leslie Spence , who had been with the laboratory since 1954. It
252-536: A Government Bacteriologist found Negri bodies in the brain of a bat with unusual habits in September 1931, finally demonstrated that rabies could be transmitted to humans by the infected saliva of vampire bats. In 1934, the Government began a program of vampire bat control, shooting, netting and trapping, while encouraging the screening off of livestock buildings and free vaccination programs for exposed livestock. After
378-523: A case reliably reported from Trinidad since an outbreak in 1914. It was discovered that a form of the disease "jungle yellow fever" was carried by Red Howler monkeys ( Alouatta macconnelli Elliot) who provided a continuous reservoir for the disease and spread by the Haemagogus s. spegazzini mosquito which normally inhabits rainforest regions, both at ground level and in the treetops. After Government felling of large stands of native forest, yellow fever
504-437: A causal association does not exist in general. Conversely, it can be (and is in some circumstances) taken by US courts, in an individual case, to justify an inference that a causal association does exist, based upon a balance of probability . The subdiscipline of forensic epidemiology is directed at the investigation of specific causation of disease or injury in individuals or groups of individuals in instances in which causation
630-506: A contact poison against several arthropods ". The WHO 's anti-malaria campaign of the 1950s and 1960s relied heavily on DDT and the results were promising, though there was a resurgence in developing countries afterwards. By October 1945, DDT was available for public sale in the United States. Although it was promoted by government and industry for use as an agricultural and household pesticide, there were also concerns about its use from
756-498: A health system responds to current population health issues but also how a health system can be managed to better respond to future potential population health issues. Examples of organizations that use population-based health management that leverage the work and results of epidemiological practice include Canadian Strategy for Cancer Control, Health Canada Tobacco Control Programs, Rick Hansen Foundation, Canadian Tobacco Control Research Initiative. Each of these organizations uses
882-521: A lesser extent, basic research in the biological sciences. Major areas of epidemiological study include disease causation, transmission , outbreak investigation, disease surveillance , environmental epidemiology , forensic epidemiology , occupational epidemiology , screening , biomonitoring , and comparisons of treatment effects such as in clinical trials . Epidemiologists rely on other scientific disciplines like biology to better understand disease processes, statistics to make efficient use of
1008-733: A patent in 1934 by Wolfgang von Leuthold. DDT's insecticidal properties were not, however, discovered until 1939 by the Swiss scientist Paul Hermann Müller , who was awarded the 1948 Nobel Prize in Physiology and Medicine for his efforts. DDT is the best-known of several chlorine -containing pesticides used in the 1940s and 1950s. During this time, the use of DDT was driven by protecting American soldiers from diseases in tropical areas. Both British and American scientists hoped to use it to control spread of malaria , typhus , dysentery , and typhoid fever among overseas soldiers, especially considering that
1134-772: A population (endemic). The term "epidemiology" appears to have first been used to describe the study of epidemics in 1802 by the Spanish physician Joaquín de Villalba [ es ] in Epidemiología Española . Epidemiologists also study the interaction of diseases in a population, a condition known as a syndemic . The term epidemiology is now widely applied to cover the description and causation of not only epidemic, infectious disease, but of disease in general, including related conditions. Some examples of topics examined through epidemiology include as high blood pressure, mental illness and obesity . Therefore, this epidemiology
1260-520: A population-based health management framework called Life at Risk that combines epidemiological quantitative analysis with demographics, health agency operational research and economics to perform: Applied epidemiology is the practice of using epidemiological methods to protect or improve the health of a population. Applied field epidemiology can include investigating communicable and non-communicable disease outbreaks, mortality and morbidity rates, and nutritional status, among other indicators of health, with
1386-1063: A possible association with liver cancer and biliary tract cancer are conflicting: workers who did not have direct occupational DDT contact showed increased risk. White men had an increased risk, but not white women or black men. Results about an association with multiple myeloma, prostate and testicular cancer, endometrial cancer and colorectal cancer have been inconclusive or generally do not support an association. A 2017 review of liver cancer studies concluded that "organochlorine pesticides, including DDT, may increase hepatocellular carcinoma risk". A 2009 review, whose co-authors included persons engaged in DDT-related litigation, reached broadly similar conclusions, with an equivocal association with testicular cancer. Case–control studies did not support an association with leukemia or lymphoma. The question of whether DDT or DDE are risk factors in breast cancer has not been conclusively answered. Several meta analyses of observational studies have concluded that there
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#17328514267831512-471: A predictor of breast cancer, and a marker of high risk". Malaria remains the primary public health challenge in many countries. In 2015, there were 214 million cases of malaria worldwide resulting in an estimated 438,000 deaths, 90% of which occurred in Africa. DDT is one of many tools to fight the disease. Its use in this context has been called everything from a "miracle weapon [that is] like Kryptonite to
1638-422: A prospective study, and confounders are more easily controlled for. However, they are more costly, and there is a greater chance of losing subjects to follow-up based on the long time period over which the cohort is followed. Cohort studies also are limited by the same equation for number of cases as for cohort studies, but, if the base incidence rate in the study population is very low, the number of cases required
1764-402: A random sample from the original population at risk. This has as a consequence that the control group can contain people with the disease under study when the disease has a high attack rate in a population. A major drawback for case control studies is that, in order to be considered to be statistically significant, the minimum number of cases required at the 95% confidence interval is related to
1890-443: A resurgence. In many areas early successes partially or completely reversed, and in some cases rates of transmission increased. The program succeeded in eliminating malaria only in areas with "high socio-economic status, well-organized healthcare systems, and relatively less intensive or seasonal malaria transmission". DDT was less effective in tropical regions due to the continuous life cycle of mosquitoes and poor infrastructure. It
2016-570: A role in the elimination of malaria in Europe and North America . Despite concerns emerging in the scientific community, and lack of research, the FDA considered it safe up to 7 parts per million in food. There was a large economic incentive to push DDT into the market and sell it to farmers, governments, and individuals to control diseases and increase food production. DDT was also a way for American influence to reach abroad through DDT-spraying campaigns. In
2142-445: A unique disease process different from any other individual ("the unique disease principle"), considering uniqueness of the exposome (a totality of endogenous and exogenous / environmental exposures) and its unique influence on molecular pathologic process in each individual. Studies to examine the relationship between an exposure and molecular pathologic signature of disease (particularly cancer ) became increasingly common throughout
2268-399: Is a core component, that is unified with management science to provide efficient and effective health care and health guidance to a population. This task requires the forward-looking ability of modern risk management approaches that transform health risk factors, incidence, prevalence and mortality statistics (derived from epidemiological analysis) into management metrics that not only guide how
2394-589: Is a major factor in the comeback of the bald eagle (the national bird of the United States ) and the peregrine falcon from near-extinction in the contiguous United States . The evolution of DDT resistance and the harm both to humans and the environment led many governments to curtail DDT use. A worldwide ban on agricultural use was formalized under the Stockholm Convention on Persistent Organic Pollutants , which has been in effect since 2004. Recognizing that total elimination in many malaria-prone countries
2520-639: Is also conferred by up-regulation of genes expressing cytochrome P450 in some insect species, as greater quantities of some enzymes of this group accelerate the toxin's metabolism into inactive metabolites. Genomic studies in the model genetic organism Drosophila melanogaster revealed that high level DDT resistance is polygenic, involving multiple resistance mechanisms. In the absence of genetic adaptation, Roberts and Andre 1994 find behavioral avoidance nonetheless provides insects with some protection against DDT. The M918T mutation event produces dramatic kdr for pyrethroids but Usherwood et al. 2005 find it
2646-426: Is applied to the inside walls of homes to kill or repel mosquitoes. This intervention, called indoor residual spraying (IRS), greatly reduces environmental damage. It also reduces the incidence of DDT resistance. For comparison, treating 40 hectares (99 acres) of cotton during a typical U.S. growing season requires the same amount of chemical to treat roughly 1,700 homes. DDT is a persistent organic pollutant that
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#17328514267832772-428: Is based upon how the pattern of the disease causes change in the function of human beings. The Greek physician Hippocrates , taught by Democritus, was known as the father of medicine , sought a logic to sickness; he is the first person known to have examined the relationships between the occurrence of disease and environmental influences. Hippocrates believed sickness of the human body to be caused by an imbalance of
2898-479: Is beyond the domain of the science of epidemiology. Epidemiology has its limits at the point where an inference is made that the relationship between an agent and a disease is causal (general causation) and where the magnitude of excess risk attributed to the agent has been determined; that is, epidemiology addresses whether an agent can cause disease, not whether an agent did cause a specific plaintiff's disease. In United States law, epidemiology alone cannot prove that
3024-477: Is clofenotane. Commercial DDT is a mixture of several closely related compounds. Due to the nature of the chemical reaction used to synthesize DDT, several combinations of ortho and para arene substitution patterns are formed. The major component (77%) is the desired p , p ' isomer . The o , p ' isomeric impurity is also present in significant amounts (15%). Dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) make up
3150-415: Is considered likely to be a human carcinogen although the majority of studies suggest it is not directly genotoxic . DDE acts as a weak androgen receptor antagonist , but not as an estrogen . p , p ' -DDT, DDT's main component, has little or no androgenic or estrogenic activity. The minor component o , p ' -DDT has weak estrogenic activity. DDT is classified as "moderately toxic" by
3276-500: Is currently unfeasible in the absence of affordable/effective alternatives for disease control, the convention exempts public health use within World Health Organization (WHO) guidelines from the ban. DDT still has limited use in disease vector control because of its effectiveness in killing mosquitos and thus reducing malarial infections, but that use is controversial due to environmental and health concerns. DDT
3402-483: Is disputed or is unclear, for presentation in legal settings. Epidemiological practice and the results of epidemiological analysis make a significant contribution to emerging population-based health management frameworks. Population-based health management encompasses the ability to: Modern population-based health management is complex, requiring a multiple set of skills (medical, political, technological, mathematical, etc.) of which epidemiological practice and analysis
3528-536: Is entirely ineffective against DDT. Scott 2019 believes this test in Drosophila oocytes holds for oocytes in general. DDT was first synthesized in 1874 by Othmar Zeidler under the supervision of Adolf von Baeyer . It was further described in 1929 in a dissertation by W. Bausch and in two subsequent publications in 1930. The insecticide properties of "multiple chlorinated aliphatic or fat-aromatic alcohols with at least one trichloromethane group" were described in
3654-527: Is famous for his investigations into the causes of the 19th-century cholera epidemics, and is also known as the father of (modern) Epidemiology. He began with noticing the significantly higher death rates in two areas supplied by Southwark Company. His identification of the Broad Street pump as the cause of the Soho epidemic is considered the classic example of epidemiology. Snow used chlorine in an attempt to clean
3780-556: Is highly hydrophobic and nearly insoluble in water but has good solubility in most organic solvents , fats and oils . DDT does not occur naturally and is synthesised by consecutive Friedel–Crafts reactions between chloral ( CCl 3 CHO ) and two equivalents of chlorobenzene ( C 6 H 5 Cl ), in the presence of an acidic catalyst . DDT has been marketed under trade names including Anofex, Cezarex, Chlorophenothane, Dicophane, Dinocide, Gesarol, Guesapon, Guesarol, Gyron, Ixodex, Neocid, Neocidol and Zerdane; INN
3906-499: Is in the term inference . Correlation, or at least association between two variables, is a necessary but not sufficient criterion for the inference that one variable causes the other. Epidemiologists use gathered data and a broad range of biomedical and psychosocial theories in an iterative way to generate or expand theory, to test hypotheses, and to make educated, informed assertions about which relationships are causal, and about exactly how they are causal. Epidemiologists emphasize that
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4032-418: Is increasing recognition that a wide range of modern data sources, many not originating from healthcare or epidemiology, can be used for epidemiological study. Such digital epidemiology can include data from internet searching, mobile phone records and retail sales of drugs. Epidemiologists employ a range of study designs from the observational to experimental and generally categorized as descriptive (involving
4158-558: Is no overall relationship between DDT exposure and breast cancer risk. The United States Institute of Medicine reviewed data on the association of breast cancer with DDT exposure in 2012 and concluded that a causative relationship could neither be proven nor disproven. A 2007 case-control study using archived blood samples found that breast cancer risk was increased 5-fold among women who were born prior to 1931 and who had high serum DDT levels in 1963. Reasoning that DDT use became widespread in 1945 and peaked around 1950, they concluded that
4284-703: Is now part of the Caribbean Epidemiology Center (Carec) in Port of Spain. The laboratory was one of four tropical virus research laboratories sponsored by the Rockefeller Foundation during the 1950s, including one in Brazil and two in Africa. Under the inspired leadership of Dr Downs the laboratory began intensive research programs and made many new discoveries including the isolating of several arthropod -borne disease-causing viruses, and new insights into
4410-410: Is one of many tools to fight malaria, which remains the primary public health challenge in many countries. WHO guidelines require that absence of DDT resistance must be confirmed before using it. Resistance is largely due to agricultural use, in much greater quantities than required for disease prevention. DDT is similar in structure to the insecticide methoxychlor and the acaricide dicofol . It
4536-540: Is readily adsorbed to soils and sediments , which can act both as sinks and as long-term sources of exposure affecting organisms. Depending on environmental conditions, its soil half-life can range from 22 days to 30 years. Routes of loss and degradation include runoff, volatilization, photolysis and aerobic and anaerobic biodegradation . Due to hydrophobic properties, in aquatic ecosystems DDT and its metabolites are absorbed by aquatic organisms and adsorbed on suspended particles, leaving little DDT dissolved in
4662-404: Is reduced by 1 ⁄ 2 . Although epidemiology is sometimes viewed as a collection of statistical tools used to elucidate the associations of exposures to health outcomes, a deeper understanding of this science is that of discovering causal relationships. " Correlation does not imply causation " is a common theme for much of the epidemiological literature. For epidemiologists, the key
4788-648: Is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population . It is a cornerstone of public health , and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare . Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results (including peer review and occasional systematic review ). Epidemiology has helped develop methodology used in clinical research , public health studies, and, to
4914-464: Is toxic to a wide range of living organisms, including marine animals such as crayfish , daphnids , sea shrimp and many species of fish . DDT, DDE and DDD magnify through the food chain , with apex predators such as raptor birds concentrating more chemicals than other animals in the same environment. They are stored mainly in body fat . DDT and DDE are resistant to metabolism; in humans, their half-lives are 6 and up to 10 years, respectively. In
5040-521: Is typically determined using DNA from peripheral blood leukocytes. Since the 2000s, genome-wide association studies (GWAS) have been commonly performed to identify genetic risk factors for many diseases and health conditions. While most molecular epidemiology studies are still using conventional disease diagnosis and classification systems, it is increasingly recognized that disease progression represents inherently heterogeneous processes differing from person to person. Conceptually, each individual has
5166-439: Is used to describe the intersection of Host , Agent , and Environment in analyzing an outbreak. Case-series may refer to the qualitative study of the experience of a single patient, or small group of patients with a similar diagnosis, or to a statistical factor with the potential to produce illness with periods when they are unexposed. The former type of study is purely descriptive and cannot be used to make inferences about
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5292-685: The Imperial College of Tropical Agriculture , the Trinidad and Tobago Health and Agriculture Departments, Arthur M. Greenhall, a world expert on vampire bats , and Dr A. E. Hill, a specialist in Tropical and Internal Diseases, with a particular interest in Dengue fever. The flourishing scientific community centered around the T.R.V.L., the New York Zoological Society's field station at Simla , and
5418-489: The South Pacific , it was sprayed aerially for malaria and dengue fever control with spectacular effects. While DDT's chemical and insecticidal properties were important factors in these victories, advances in application equipment coupled with competent organization and sufficient manpower were also crucial to the success of these programs. In 1945, DDT was made available to farmers as an agricultural insecticide and played
5544-476: The " one cause – one effect " understanding is a simplistic mis-belief. Most outcomes, whether disease or death, are caused by a chain or web consisting of many component causes. Causes can be distinguished as necessary, sufficient or probabilistic conditions. If a necessary condition can be identified and controlled (e.g., antibodies to a disease agent, energy in an injury), the harmful outcome can be avoided (Robertson, 2015). One tool regularly used to conceptualize
5670-459: The "who, what, where and when of health-related state occurrence". However, analytical observations deal more with the 'how' of a health-related event. Experimental epidemiology contains three case types: randomized controlled trials (often used for a new medicine or drug testing), field trials (conducted on those at a high risk of contracting a disease), and community trials (research on social originating diseases). The term 'epidemiologic triad'
5796-507: The 1944 issue of Life magazine there was a feature regarding the Italian program showing pictures of American public health officials in uniforms spraying DDT on Italian families. In 1955, the World Health Organization commenced a program to eradicate malaria in countries with low to moderate transmission rates worldwide, relying largely on DDT for mosquito control and rapid diagnosis and treatment to reduce transmission. The program eliminated
5922-715: The 1950s the federal government began tightening regulations governing its use. These events received little attention. Women like Dorothy Colson and Mamie Ella Plyler of Claxton, Georgia , gathered evidence about DDT's effects and wrote to the Georgia Department of Public Health, the National Health Council in New York City, and other organizations. In 1957 The New York Times reported an unsuccessful struggle to restrict DDT use in Nassau County, New York , and
6048-515: The 2000s. However, the use of molecular pathology in epidemiology posed unique challenges, including lack of research guidelines and standardized statistical methodologies, and paucity of interdisciplinary experts and training programs. Furthermore, the concept of disease heterogeneity appears to conflict with the long-standing premise in epidemiology that individuals with the same disease name have similar etiologies and disease processes. To resolve these issues and advance population health science in
6174-504: The 2010s. By 2012, it was recognized that many pathogens' evolution is rapid enough to be highly relevant to epidemiology, and that therefore much could be gained from an interdisciplinary approach to infectious disease integrating epidemiology and molecular evolution to "inform control strategies, or even patient treatment." Modern epidemiological studies can use advanced statistics and machine learning to create predictive models as well as to define treatment effects. There
6300-556: The Austrian chemist Othmar Zeidler . DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939. DDT was used in the second half of World War II to limit the spread of the insect-borne diseases malaria and typhus among civilians and troops. Müller was awarded the Nobel Prize in Physiology or Medicine in 1948 "for his discovery of the high efficiency of DDT as
6426-618: The EPA's internal staff stating that DDT was not an imminent danger. However, these findings were criticized, as they were performed mostly by economic entomologists inherited from the United States Department of Agriculture , who many environmentalists felt were biased towards agribusiness and understated concerns about human health and wildlife. The decision thus created controversy. The EPA held seven months of hearings in 1971–1972, with scientists giving evidence for and against DDT. In
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#17328514267836552-484: The Imperial College of Agriculture, provided an exciting pool of top-notch scholars whose interests often extended well past their immediate jobs. Much useful research was accomplished in these years in fields as diverse as archeology , the mating of butterflies and fiddler crabs , ornithology , and parasitology . The laboratory also played host to constant stream of distinguishing visiting scientists from around
6678-554: The OR, a RR greater than 1 shows association, where the conclusion can be read "those with the exposure were more likely to develop the disease." Prospective studies have many benefits over case control studies. The RR is a more powerful effect measure than the OR, as the OR is just an estimation of the RR, since true incidence cannot be calculated in a case control study where subjects are selected based on disease status. Temporality can be established in
6804-582: The Palos Verdes Shelf area of the Montrose Chemical Superfund site exhibited continued thin-shell problems, though DDT's role in the decline of the California condor is disputed. The biological thinning mechanism is not entirely understood, but DDE appears to be more potent than DDT, and strong evidence indicates that p , p ' -DDE inhibits calcium ATPase in the membrane of
6930-587: The U.S. National Toxicology Program (NTP) and "moderately hazardous" by WHO, based on the rat oral LD 50 of 113 mg/kg. Indirect exposure is considered relatively non-toxic for humans. Primarily through the tendency for DDT to build up in areas of the body with high lipid content, chronic exposure can affect reproductive capabilities and the embryo or fetus. In 2015, the International Agency for Research on Cancer classified DDT as Group 2A "probably carcinogenic to humans". Previous assessments by
7056-456: The U.S. National Toxicology Program classified it as "reasonably anticipated to be a carcinogen" and by the EPA classified DDT, DDE and DDD as class B2 "probable" carcinogens ; these evaluations were based mainly on animal studies. A 2005 Lancet review stated that occupational DDT exposure was associated with increased pancreatic cancer risk in 2 case control studies, but another study showed no DDE dose-effect association. Results regarding
7182-716: The US before the 1972 ban. Usage peaked in 1959 at about 36,000 tonnes. China ceased production in 2007, leaving India the only country still manufacturing DDT; it is the largest consumer. In 2009, 3,314 tonnes were produced for malaria control and visceral leishmaniasis . In recent years, in addition to India, just seven other countries, all in Africa, are still using DDT. In insects, DDT opens voltage-sensitive sodium ion channels in neurons , causing them to fire spontaneously, which leads to spasms and eventual death. Insects with certain mutations in their sodium channel gene are resistant to DDT and similar insecticides. DDT resistance
7308-785: The United States, these chemicals were detected in almost all human blood samples tested by the Centers for Disease Control in 2005, though their levels have sharply declined since most uses were banned. Estimated dietary intake has declined, although FDA food tests commonly detect it. Despite being banned for many years, in 2018 research showed that DDT residues are still present in European soils and Spanish rivers. The chemical and its breakdown products DDE and DDD caused eggshell thinning and population declines in multiple North American and European bird of prey species. Both laboratory experiments and field studies confirmed this effect. The effect
7434-717: The accuracy of giving animals high amounts of pesticides for cancer potential. Industry sought to overturn the ban, while the EDF wanted a comprehensive ban. The cases were consolidated, and in 1973 the United States Court of Appeals for the District of Columbia Circuit ruled that the EPA had acted properly in banning DDT. During the late 1970s, the EPA also began banning organochlorines, pesticides that were chemically similar to DDT. These included aldrin, dieldrin, chlordane, heptachlor, toxaphene, and mirex. Some uses of DDT continued under
7560-439: The ages of 14–20 were a critical period in which DDT exposure leads to increased risk. This study, which suggests a connection between DDT exposure and breast cancer that would not be picked up by most studies, has received variable commentary in third-party reviews. One review suggested that "previous studies that measured exposure in older women may have missed the critical period". The National Toxicology Program notes that while
7686-407: The assessment of data covering time, place, and person), analytic (aiming to further examine known associations or hypothesized relationships), and experimental (a term often equated with clinical or community trials of treatments and other interventions). In observational studies, nature is allowed to "take its course", as epidemiologists observe from the sidelines. Conversely, in experimental studies,
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#17328514267837812-467: The balance of impurities in commercial samples. DDE and DDD are also the major metabolites and environmental breakdown products. DDT, DDE and DDD are sometimes referred to collectively as DDX. DDT has been formulated in multiple forms, including solutions in xylene or petroleum distillates , emulsifiable concentrates , water- wettable powders , granules, aerosols , smoke candles and charges for vaporizers and lotions. From 1950 to 1980, DDT
7938-508: The beginning. Opposition to DDT was focused by the 1962 publication of Rachel Carson 's book Silent Spring . It talked about environmental impacts that correlated with the widespread use of DDT in agriculture in the United States, and it questioned the logic of broadcasting potentially dangerous chemicals into the environment with little prior investigation of their environmental and health effects. The book cited claims that DDT and other pesticides caused cancer and that their agricultural use
8064-414: The case control study. However, the point estimate generated is the relative risk (RR), which is the probability of disease for a person in the exposed group, P e = A / ( A + B ) over the probability of disease for a person in the unexposed group, P u = C / ( C + D ), i.e. RR = P e / P u . As with
8190-429: The causation of the disease. Case-control studies are usually faster and more cost-effective than cohort studies but are sensitive to bias (such as recall bias and selection bias ). The main challenge is to identify the appropriate control group; the distribution of exposure among the control group should be representative of the distribution in the population that gave rise to the cases. This can be achieved by drawing
8316-427: The cause-and-effect hypothesis and none can be required sine qua non ." Epidemiological studies can only go to prove that an agent could have caused, but not that it did cause, an effect in any particular case: Epidemiology is concerned with the incidence of disease in populations and does not address the question of the cause of an individual's disease. This question, sometimes referred to as specific causation,
8442-528: The dangers of using the pesticide DDT in agriculture. DDT had been researched and manufactured in St. Louis by the Michigan Chemical Corporation , later purchased by Velsicol Chemical Corporation , and had become an important part of the local economy. Citing research performed by Michigan State University in 1946, Robinson, a past president of the local Conservation Club, opined that: perhaps
8568-445: The data and draw appropriate conclusions, social sciences to better understand proximate and distal causes, and engineering for exposure assessment . Epidemiology , literally meaning "the study of what is upon the people", is derived from Greek epi 'upon, among' demos 'people, district' and logos 'study, word, discourse', suggesting that it applies only to human populations. However,
8694-617: The disease in "North America, Europe, the former Soviet Union ", and in " Taiwan , much of the Caribbean , the Balkans , parts of northern Africa, the northern region of Australia, and a large swath of the South Pacific" and dramatically reduced mortality in Sri Lanka and India. However, failure to sustain the program, increasing mosquito tolerance to DDT, and increasing parasite tolerance led to
8820-497: The disease to the cases in the series. A prospective study would involve following the case series over time to evaluate the disease's natural history. The latter type, more formally described as self-controlled case-series studies, divide individual patient follow-up time into exposed and unexposed periods and use fixed-effects Poisson regression processes to compare the incidence rate of a given outcome between exposed and unexposed periods. This technique has been extensively used in
8946-535: The eggs of peregrine falcons and California condors and finding that increased levels corresponded with thinner shells. In response to an EDF suit, the U.S. District Court of Appeals in 1971 ordered the EPA to begin the de-registration procedure for DDT. After an initial six-month review process, William Ruckelshaus , the Agency's first Administrator rejected an immediate suspension of DDT's registration, citing studies from
9072-425: The environment and were endangering human health. Silent Spring was a best seller, and public reaction to it launched the modern environmental movement in the United States. The year after it appeared, President John F. Kennedy ordered his Science Advisory Committee to investigate Carson's claims. The committee's report "add[ed] up to a fairly thorough-going vindication of Rachel Carson's Silent Spring thesis", in
9198-612: The epidemiologist is the one in control of all of the factors entering a certain case study. Epidemiological studies are aimed, where possible, at revealing unbiased relationships between exposures such as alcohol or smoking, biological agents , stress , or chemicals to mortality or morbidity . The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. Modern epidemiologists use informatics and infodemiology as tools. Observational studies have two components, descriptive and analytical. Descriptive observations pertain to
9324-544: The epidemiology of key virus diseases including yellow fever , dengue fever , and rabies . Downs headed a team of dedicated researchers including Dr. Charles R. Anderson (Virologist), Dr Leslie Spence (Epidemiologist), Dr Thomas Aitkens (Entomologist) and Dr Brooke Worth (Mammologist and Ornithologist). They worked very closely with other scientists in Trinidad, particularly those at the New York Zoological Society 's research station headed by Dr William Beebe ,
9450-771: The era of molecular precision medicine , "molecular pathology" and "epidemiology" was integrated to create a new interdisciplinary field of " molecular pathological epidemiology " (MPE), defined as "epidemiology of molecular pathology and heterogeneity of disease". In MPE, investigators analyze the relationships between (A) environmental, dietary, lifestyle and genetic factors; (B) alterations in cellular or extracellular molecules; and (C) evolution and progression of disease. A better understanding of heterogeneity of disease pathogenesis will further contribute to elucidate etiologies of disease. The MPE approach can be applied to not only neoplastic diseases but also non-neoplastic diseases. The concept and paradigm of MPE have become widespread in
9576-564: The field and advanced methods to study cancer, a disease with patterns and mode of occurrences that could not be suitably studied with the methods developed for epidemics of infectious diseases. Geography pathology eventually combined with infectious disease epidemiology to make the field that is epidemiology today. Another breakthrough was the 1954 publication of the results of a British Doctors Study , led by Richard Doll and Austin Bradford Hill , which lent very strong statistical support to
9702-507: The former western German states. By 1991, total bans, including for disease control, were in place in at least 26 countries; for example, Cuba in 1970, the US in the 1980s, Singapore in 1984, Chile in 1985, and the Republic of Korea in 1986. The Stockholm Convention on Persistent Organic Pollutants , which took effect in 2004, put a global ban on several persistent organic pollutants , and restricted DDT use to vector control . The convention
9828-405: The four humors (black bile, yellow bile, blood, and phlegm). The cure to the sickness was to remove or add the humor in question to balance the body. This belief led to the application of bloodletting and dieting in medicine. He coined the terms endemic (for diseases usually found in some places but not in others) and epidemic (for diseases that are seen at some times but not others). In
9954-458: The general population of patients with that disease. These types of studies, in which an astute clinician identifies an unusual feature of a disease or a patient's history, may lead to a formulation of a new hypothesis. Using the data from the series, analytic studies could be done to investigate possible causal factors. These can include case-control studies or prospective studies. A case-control study would involve matching comparable controls without
10080-404: The greatest danger from D.D.T. is that its extensive use in farm areas is most likely to upset the natural balances, not only killing beneficial insects in great number but by bringing about the death of fish, birds, and other forms of wild life either by their feeding on insects killed by D.D.T. or directly by ingesting the poison. As its production and use increased, public response was mixed. At
10206-411: The health measures taken it did not develop into a widespread epidemic in Trinidad itself. An attempt was made to totally quarantine the island just before Christmas, 1954, but the disease quickly spread to the nearby mainland of Venezuela and, from there, all the way to southern Mexico, probably killing several thousand people in the process. Large-scale surveys were made of viruses and antigens in
10332-536: The issue came to the attention of the popular naturalist-author Rachel Carson when a friend, Olga Huckins , wrote to her including an article she had written in the Boston Globe about the devastation of her local bird population after DDT spraying. William Shawn , editor of The New Yorker , urged her to write a piece on the subject, which developed into her 1962 book Silent Spring . The book argued that pesticides , including DDT, were poisoning both wildlife and
10458-508: The large Nariva Swamp in southeastern Trinidad and a large tree station was built in the Vega de Oropouche rainforest near Sangre Grande with platforms at 60, 90 and 120 feet (18, 27 and 36.6 metres) to facilitate collecting mosquitoes at various levels in the rainforest, including the forest canopy . Dr. H. Metivier, a Veterinary Surgeon, who established in 1931 the connection between the bites of bats and paralytic rabies , and Dr. J. L. Pawan,
10584-575: The link between tobacco smoking and lung cancer . In the late 20th century, with the advancement of biomedical sciences, a number of molecular markers in blood, other biospecimens and environment were identified as predictors of development or risk of a certain disease. Epidemiology research to examine the relationship between these biomarkers analyzed at the molecular level and disease was broadly named " molecular epidemiology ". Specifically, " genetic epidemiology " has been used for epidemiology of germline genetic variation and disease. Genetic variation
10710-427: The local population, as well as domestic and wild animals. At the time the laboratory was established there were a number of common but unidentified disease-causing virus fevers in Trinidad, usually referred to by descriptive names such as "Trinidad 3-day fever", Trinidad 5-day fever", and the like. Some of these were soon isolated and identified. A semi-permanent bush camp was set up at Bush Bush Wildlife Sanctuary in
10836-403: The main etiological work that brought forward the concept. His concepts were still being considered in analysing SARS outbreak by WHO in 2004 in the context of traditional Chinese medicine. Another pioneer, Thomas Sydenham (1624–1689), was the first to distinguish the fevers of Londoners in the later 1600s. His theories on cures of fevers met with much resistance from traditional physicians at
10962-493: The majority of studies have not found a relationship between DDT exposure and breast cancer that positive associations have been seen in a "few studies among women with higher levels of exposure and among certain subgroups of women". A 2015 case control study identified a link (odds ratio 3.4) between in-utero exposure (as estimated from archived maternal blood samples) and breast cancer diagnosis in daughters. The findings "support classification of DDT as an endocrine disruptor,
11088-448: The middle of the 16th century, a doctor from Verona named Girolamo Fracastoro was the first to propose a theory that the very small, unseeable, particles that cause disease were alive. They were considered to be able to spread by air, multiply by themselves and to be destroyable by fire. In this way he refuted Galen 's miasma theory (poison gas in sick people). In 1543 he wrote a book De contagione et contagiosis morbis , in which he
11214-933: The mosquitoes", to "toxic colonialism". Before DDT, eliminating mosquito breeding grounds by drainage or poisoning with Paris green or pyrethrum was sometimes successful. In parts of the world with rising living standards, the elimination of malaria was often a collateral benefit of the introduction of window screens and improved sanitation. A variety of usually simultaneous interventions represents best practice. These include antimalarial drugs to prevent or treat infection; improvements in public health infrastructure to diagnose, sequester and treat infected individuals; bednets and other methods intended to keep mosquitoes from biting humans; and vector control strategies such as larviciding with insecticides, ecological controls such as draining mosquito breeding grounds or introducing fish to eat larvae and indoor residual spraying (IRS) with insecticides, possibly including DDT. IRS involves
11340-506: The multicausality associated with disease is the causal pie model . In 1965, Austin Bradford Hill proposed a series of considerations to help assess evidence of causation, which have come to be commonly known as the " Bradford Hill criteria ". In contrast to the explicit intentions of their author, Hill's considerations are now sometimes taught as a checklist to be implemented for assessing causality. Hill himself said "None of my nine viewpoints can bring indisputable evidence for or against
11466-417: The odds of exposure in the cases (A/C) to the odds of exposure in the controls (B/D), i.e. OR = (AD/BC). If the OR is significantly greater than 1, then the conclusion is "those with the disease are more likely to have been exposed", whereas if it is close to 1 then the exposure and disease are not likely associated. If the OR is far less than one, then this suggests that the exposure is a protective factor in
11592-498: The odds ratio by the equation: where N is the ratio of cases to controls. As the odds ratio approaches 1, the number of cases required for statistical significance grows towards infinity; rendering case-control studies all but useless for low odds ratios. For instance, for an odds ratio of 1.5 and cases = controls, the table shown above would look like this: For an odds ratio of 1.1: Cohort studies select subjects based on their exposure status. The study subjects should be at risk of
11718-475: The opening of the Virus laboratory in 1953 basic research on bats and the transmission of rabies progressed rapidly under the able direction of Arthur Greenhall, a Government Zoologist. Some of the main viruses isolated at T.R.V.L. (new discoveries marked with an asterisk): 10°40′N 61°31′W / 10.667°N 61.517°W / 10.667; -61.517 Epidemiologist Epidemiology
11844-414: The outcome under investigation at the beginning of the cohort study; this usually means that they should be disease free when the cohort study starts. The cohort is followed through time to assess their later outcome status. An example of a cohort study would be the investigation of a cohort of smokers and non-smokers over time to estimate the incidence of lung cancer. The same 2×2 table is constructed as with
11970-400: The prevailing Miasma Theory of the time, a model of disease in which poor air quality was blamed for illness. This was used to rationalize high rates of infection in impoverished areas instead of addressing the underlying issues of poor nutrition and sanitation, and was proven false by his work. Other pioneers include Danish physician Peter Anton Schleisner , who in 1849 related his work on
12096-627: The prevention of the epidemic of neonatal tetanus on the Vestmanna Islands in Iceland . Another important pioneer was Hungarian physician Ignaz Semmelweis , who in 1847 brought down infant mortality at a Vienna hospital by instituting a disinfection procedure. His findings were published in 1850, but his work was ill-received by his colleagues, who discontinued the procedure. Disinfection did not become widely practiced until British surgeon Joseph Lister 'discovered' antiseptics in 1865 in light of
12222-597: The public health exemption. For example, in June 1979, the California Department of Health Services was permitted to use DDT to suppress flea vectors of bubonic plague . DDT continued to be produced in the United States for foreign markets until 1985, when over 300 tons were exported. In the 1970s and 1980s, agricultural use was banned in most developed countries, beginning with Hungary in 1968 – although in practice it continued to be used through at least 1970. This
12348-429: The purpose of communicating the results to those who can implement appropriate policies or disease control measures. DDT Dichlorodiphenyltrichloroethane , commonly known as DDT , is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride . Originally developed as an insecticide , it became infamous for its environmental impacts . DDT was first synthesized in 1874 by
12474-581: The pyrethrum was harder to access since it came mainly from Japan. Due to the potency of DDT, it was not long before America's War Production Board placed it on military supply lists in 1942 and 1943 and encouraged its production for overseas use. Enthusiasm regarding DDT became obvious through the American government's advertising campaigns of posters depicting Americans fighting the Axis powers and insects and through media publications celebrating its military uses. In
12600-508: The region's food web . Medical researchers in 1974 found a measurable and significant difference in the presence of DDT in human milk between mothers who lived in New Brunswick and mothers who lived in Nova Scotia , "possibly because of the wider use of insecticide sprays in the past". Because of its lipophilic properties, DDT can bioaccumulate , especially in predatory birds . DDT
12726-402: The same population that gave rise to the cases. The case-control study looks back through time at potential exposures that both groups (cases and controls) may have encountered. A 2×2 table is constructed, displaying exposed cases (A), exposed controls (B), unexposed cases (C) and unexposed controls (D). The statistic generated to measure association is the odds ratio (OR), which is the ratio of
12852-471: The same time that DDT was hailed as part of the "world of tomorrow", concerns were expressed about its potential to kill harmless and beneficial insects (particularly pollinators ), birds, fish, and eventually humans. The issue of toxicity was complicated, partly because DDT's effects varied from species to species, and partly because consecutive exposures could accumulate, causing damage comparable to large doses. A number of states attempted to regulate DDT. In
12978-418: The shell gland and reduces the transport of calcium carbonate from blood into the eggshell gland. This results in a dose-dependent thickness reduction. Other evidence indicates that o,p'-DDT disrupts female reproductive tract development, later impairing eggshell quality. Multiple mechanisms may be at work, or different mechanisms may operate in different species. DDT is an endocrine disruptor . It
13104-403: The specific goal of enacting a ban on DDT. Victor Yannacone , Charles F. Wurster , Art Cooley and others in the group had all witnessed bird kills or declines in bird populations and suspected that DDT was the cause. In their campaign against the chemical, the EDF petitioned the government for a ban and filed lawsuits. Around this time, toxicologist David Peakall was measuring DDE levels in
13230-456: The study of adverse reactions to vaccination and has been shown in some circumstances to provide statistical power comparable to that available in cohort studies. Case-control studies select subjects based on their disease status. It is a retrospective study. A group of individuals that are disease positive (the "case" group) is compared with a group of disease negative individuals (the "control" group). The control group should ideally come from
13356-526: The summer of 1972, Ruckelshaus announced the cancellation of most uses of DDT – exempting public health uses under some conditions. Again, this caused controversy. Immediately after the announcement, both the EDF and the DDT manufacturers filed suit against EPA. Many in the agricultural community were concerned that food production would be severely impacted, while proponents of pesticides warned of increased breakouts of insect-borne diseases and questioned
13482-439: The term is widely used in studies of zoological populations (veterinary epidemiology), although the term " epizoology " is available, and it has also been applied to studies of plant populations (botanical or plant disease epidemiology ). The distinction between "epidemic" and "endemic" was first drawn by Hippocrates , to distinguish between diseases that are "visited upon" a population (epidemic) from those that "reside within"
13608-702: The time. He was not able to find the initial cause of the smallpox fever he researched and treated. John Graunt , a haberdasher and amateur statistician, published Natural and Political Observations ... upon the Bills of Mortality in 1662. In it, he analysed the mortality rolls in London before the Great Plague , presented one of the first life tables , and reported time trends for many diseases, new and old. He provided statistical evidence for many theories on disease, and also refuted some widespread ideas on them. John Snow
13734-671: The treatment of interior walls and ceilings with insecticides. It is particularly effective against mosquitoes, since many species rest on an indoor wall before or after feeding. DDT is one of 12 WHO–approved IRS insecticides. The WHO's anti-malaria campaign of the 1950s and 1960s relied heavily on DDT and the results were promising, though temporary in developing countries. Experts tie malarial resurgence to multiple factors, including poor leadership, management and funding of malaria control programs; poverty; civil unrest; and increased irrigation . The evolution of resistance to first-generation drugs (e.g. chloroquine ) and to insecticides exacerbated
13860-538: The treaty is arguably better than the status quo going into the negotiations. For the first time, there is now an insecticide which is restricted to vector control only, meaning that the selection of resistant mosquitoes will be slower than before." Despite the worldwide ban, agricultural use continued in India, North Korea, and possibly elsewhere. As of 2013, an estimated 3,000 to 4,000 tons of DDT were produced for disease vector control , including 2,786 tons in India. DDT
13986-537: The water (however, its half-life in aquatic environments is listed by the National Pesticide Information Center as 150 years ). Its breakdown products and metabolites, DDE and DDD, are also persistent and have similar chemical and physical properties. DDT and its breakdown products are transported from warmer areas to the Arctic by the phenomenon of global distillation , where they then accumulate in
14112-413: The water and removed the handle; this ended the outbreak. This has been perceived as a major event in the history of public health and regarded as the founding event of the science of epidemiology, having helped shape public health policies around the world. However, Snow's research and preventive measures to avoid further outbreaks were not fully accepted or put into practice until after his death due to
14238-478: The words of the journal Science , and recommended a phaseout of "persistent toxic pesticides". In 1965, the U.S. military removed DDT from the military supply system due in part to the development of resistance by body lice to DDT; it was replaced by lindane . DDT became a prime target of the growing anti-chemical and anti-pesticide movements, and in 1967 a group of scientists and lawyers founded Environmental Defense (later Environmental Defense Fund, EDF) with
14364-628: The work of Louis Pasteur . In the early 20th century, mathematical methods were introduced into epidemiology by Ronald Ross , Janet Lane-Claypon , Anderson Gray McKendrick , and others. In a parallel development during the 1920s, German-Swiss pathologist Max Askanazy and others founded the International Society for Geographical Pathology to systematically investigate the geographical pathology of cancer and other non-infectious diseases across populations in different regions. After World War II, Richard Doll and other non-pathologists joined
14490-512: The world, many of them conducting cutting-edge research in their fields, as well as photographers and illustrators from the National Geographic and other magazines, as well as providing first-class training and jobs for local people. The discovery of a sick Red Howler monkey, (who was found to be suffering from yellow fever ) in 1953 provided the first indication that yellow fever was still endemic in Trinidad although there had not been
14616-466: Was a threat to wildlife, particularly birds. Although Carson never directly called for an outright ban on the use of DDT, its publication was a seminal event for the environmental movement and resulted in a large public outcry that eventually led, in 1972, to a ban on DDT's agricultural use in the United States. Along with the passage of the Endangered Species Act , the United States ban on DDT
14742-418: Was abandoned in 1969 and attention instead focused on controlling and treating the disease. Spraying programs (especially using DDT) were curtailed due to concerns over safety and environmental effects, as well as problems in administrative, managerial and financial implementation. Efforts shifted from spraying to the use of bednets impregnated with insecticides and other interventions. By October 1945, DDT
14868-449: Was applied in sub-Saharan Africa by various colonial states, but the 'global' WHO eradication program didn't include the region. Mortality rates in that area never declined to the same dramatic extent, and now constitute the bulk of malarial deaths worldwide, especially following the disease's resurgence as a result of resistance to drug treatments and the spread of the deadly malarial variant caused by Plasmodium falciparum . Eradication
14994-502: Was available for public sale in the United States, used both as an agricultural pesticide and as a household insecticide. Although its use was promoted by government and the agricultural industry, US scientists such as FDA pharmacologist Herbert O. Calvery expressed concern over possible hazards associated with DDT as early as 1944. In 1947, Bradbury Robinson , a physician and nutritionist practicing in St. Louis, Michigan , warned of
15120-515: Was extensively used in agriculture – more than 40,000 tonnes each year worldwide – and it has been estimated that a total of 1.8 million tonnes have been produced globally since the 1940s. In the United States, it was manufactured by some 15 companies, including Monsanto , Ciba , Montrose Chemical Company , Pennwalt , and Velsicol Chemical Corporation . Production peaked in 1963 at 82,000 tonnes per year. More than 600,000 tonnes (1.35 billion pounds) were applied in
15246-637: Was first conclusively proven at Bellow Island in Lake Michigan during University of Michigan -funded studies on American herring gulls in the mid-1960s. DDE-related eggshell thinning is considered a major reason for the decline of the bald eagle , brown pelican , peregrine falcon and osprey . However, birds vary in their sensitivity to these chemicals, with birds of prey , waterfowl and song birds being more susceptible than chickens and related species . Even in 2010, California condors that feed on sea lions at Big Sur that in turn feed in
15372-620: Was followed by Norway and Sweden in 1970, West Germany and the United States in 1972, but not in the United Kingdom until 1984. In contrast to West Germany, in the German Democratic Republic DDT was used until 1988. Especially of relevance were large-scale applications in forestry in the years 1982–1984, with the aim to combat bark beetle and pine moth . As a consequence, DDT-concentrations in eastern German forest soils are still significantly higher compared to soils in
15498-522: Was imminent and Downs and Hill began a program of inoculating health workers and stockpiling vaccine. Trinidad health authorities followed up with large-scale vaccination and intensive anti- aegypti measures including public education, regular inspection for breeding sites, and spraying of domestic residences with DDT . In spite of these measures, and the fact that an estimated 80% of the population of Port of Spain were immune to yellow fever and dengue, several more cases were soon reported. Most probably due to
15624-441: Was isolated from a patient from Cumaca in the northern range in 1954. It soon began to spread to humans and be transmitted by the common Aedes aegypti mosquitoes. Blood specimens were taken from over 4,500 humans in late 1953 and early 1954, and checked to detect the presence of a wide variety of known viruses. Over 15% showed antibodies to yellow fever and more human cases quickly followed. Warnings were made that an epidemic
15750-614: Was ratified by more than 170 countries. Recognizing that total elimination in many malaria-prone countries is currently unfeasible in the absence of affordable/effective alternatives, the convention exempts public health use within World Health Organization (WHO) guidelines from the ban. Resolution 60.18 of the World Health Assembly commits WHO to the Stockholm Convention's aim of reducing and ultimately eliminating DDT. Malaria Foundation International states, "The outcome of
15876-664: Was the first to promote personal and environmental hygiene to prevent disease. The development of a sufficiently powerful microscope by Antonie van Leeuwenhoek in 1675 provided visual evidence of living particles consistent with a germ theory of disease . During the Ming dynasty , Wu Youke (1582–1652) developed the idea that some diseases were caused by transmissible agents, which he called Li Qi (戾气 or pestilential factors) when he observed various epidemics rage around him between 1641 and 1644. His book Wen Yi Lun (瘟疫论, Treatise on Pestilence/Treatise of Epidemic Diseases) can be regarded as
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