Misplaced Pages

#607392

121-460: Toxoplasmosis is usually spread by eating poorly cooked food that contains cysts , by exposure to infected cat feces, or from an infected woman to her baby during pregnancy. Rarely, the disease may be spread by blood transfusion or other organ transplant. It is not otherwise spread between people. The parasite is known to reproduce sexually only in the cat family . However, it can infect most types of warm-blooded animals , including humans. Diagnosis

242-469: A systematic review , in comparison with an accepted reference method. Most of them were enzyme-immunoassays, followed by agglutination tests, immunochromatographic tests, and a Western-Blot assay. The mean sensitivity of IgG assays ranged from 89.7% to 100% for standard titers and from 13.4% to 99.2% for low IgG titers. A few studies pointed out the ability of some methods, especially WB to detect IgG early after primary infection. The specificity of IgG assays

363-449: A bet-hedging mechanism for food availability or perhaps an adaptation to variation in food levels throughout a growing season. While the cyst component itself is not pathogenic, the formation of a cyst is what gives Giardia its primary tool of survival and its ability to spread from host to host. Ingestion of contaminated water, foods, or fecal matter gives rise to the most commonly diagnosed intestinal disease, giardiasis . Whereas it

484-407: A calcium-dependent pathway. Another study suggests that the parasite can directly affect calcium being released from calcium stores, which are important for the signalling processes of cells. The mechanisms above allow T. gondii to persist in a host. Some limiting factors for the toxoplasma is that its influence on the host cells is stronger in a weak immune system and is quantity-dependent, so

605-465: A central band known as the visual streak. Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The farthest edge of the retina is defined by the ora serrata . The distance from one ora to the other (or macula), the most sensitive area along the horizontal meridian , is about 32 mm. In section, the retina is no more than 0.5 mm thick. It has three layers of nerve cells and two of synapses , including

726-483: A child's hearing. Up to 30% of newborns have some degree of sensorineural hearing loss. The child's communication skills may also be affected. A study published in 2010 looked at 106 patients, all of whom received toxoplasmosis treatment prior to 2.5 months. Of this group, 26.4% presented with language disorders. Treatment is recommended for people with serious health problems, such as people with HIV whose CD4 counts are under 200 cells/mm. Trimethoprim/sulfamethoxazole

847-610: A common intestinal parasite that causes dysentery , has to endure the highly acidic environment of the stomach before it reaches the intestine and various unpredictable conditions like desiccation and lack of nutrients while it is outside the host. An encysted form is well suited to survive such extreme conditions, although protozoan cysts are less resistant to adverse conditions compared to bacterial cysts. Cytoplasmic dehydration, high autophagic activity, nuclear condensation, and decrease of cell volume are all indicators of encystment initiation in ciliated protists. In addition to survival,

968-412: A compound known to confer resistance to extreme heat. Microbial cysts have been likened to modified vegetative cells with the addition of a specialized capsule. Importantly, encystment is a process observed to precede cell division, while the formation of an endospore involves non-reproductive cellular division. The study of the encystment process was mostly confined to the 1970s and '80s, resulting in

1089-579: A considered view that the bird retina depends for nutrition and oxygen supply on a specialized organ, called the "pecten" or pecten oculi , located on the blind spot or optic disk. This organ is extremely rich in blood vessels and is thought to supply nutrition and oxygen to the bird retina by diffusion through the vitreous body. The pecten is highly rich in alkaline phosphatase activity and polarized cells in its bridge portion – both befitting its secretory role. Pecten cells are packed with dark melanin granules, which have been theorized to keep this organ warm with

1210-630: A day, the oocyst undergoes a process called sporulation and becomes potentially pathogenic. In addition to cats, birds and mammals including human beings are also intermediate hosts of the parasite and are involved in the transmission process. However the pathogenicity varies with the age and species involved in infection and the mode of transmission of T. gondii . Toxoplasmosis may also be transmitted through solid organ transplants. Toxoplasma-seronegative recipients who receive organs from recently infected Toxoplasma-seropositive donors are at risk. Organ recipients who have latent toxoplasmosis are at risk of

1331-504: A definite diagnosis. A failed trial of antimicrobial therapy ( pyrimethamine , sulfadiazine , and folinic acid ( USAN : leucovorin)), makes an alternative diagnosis more likely. T. gondii may also be detected in blood , amniotic fluid , or cerebrospinal fluid by using polymerase chain reaction . T. gondii may exist in a host as an inactive cyst that would likely evade detection. Serological testing can detect T. gondii antibodies in blood serum, using methods including

SECTION 10

#1732875832608

1452-460: A descriptive term that conveys more precisely the parasitological nature of this stage. After proliferating, tachyzoites convert into bradyzoites , which are inside latent intracellular tissue cysts that form mainly in the muscles and brain. The formation of cysts is in part triggered by the pressure of the host immune system. The bradyzoites (also called "bradyzoic merozoites") are not responsive to antibiotics. Bradyzoites, once formed, can remain in

1573-672: A fully functioning immune system to develop severe symptoms following infection. People with weakened immune systems are likely to experience headache, confusion, poor coordination, seizures, lung problems that may resemble tuberculosis or Pneumocystis jirovecii pneumonia (a common opportunistic infection that occurs in people with AIDS), or chorioretinitis caused by severe inflammation of the retina (ocular toxoplasmosis). Young children and immunocompromised people, such as those with HIV/AIDS, those taking certain types of chemotherapy , or those who have recently received an organ transplant , may develop severe toxoplasmosis. This can cause damage to

1694-607: A large number of T. gondii per host cell cause a more severe effect. The effect on the host also depends on the strength of the host immune system. Immunocompetent individuals do not normally show severe symptoms or any at all, while fatality or severe complications can result in immunocompromised individuals. T. gondii has been shown to produce a protein called GRA28, released by the MYR1 secretory pathway, which interferes with gene expression in infected cells and results in cells that behave like dendritic cells, becoming highly mobile in

1815-509: A linear model, this response profile is well described by a difference of Gaussians and is the basis for edge detection algorithms. Beyond this simple difference, ganglion cells are also differentiated by chromatic sensitivity and the type of spatial summation. Cells showing linear spatial summation are termed X cells (also called parvocellular, P, or midget ganglion cells), and those showing non-linear summation are Y cells (also called magnocellular, M, or parasol retinal ganglion cells), although

1936-429: A method for dispersal and as a way for an organism to survive in unfavorable environmental conditions. These two functions can be combined when a microbe needs to be able to survive harsh conditions between habitable environments (such as between hosts) in order to disperse. Cysts can also be sites for nuclear reorganization and cell division, and in parasitic species they are often the infectious stage between hosts. When

2057-403: A more complex structure such as the inverted retina can generally come about as a consequence of two alternate processes - an advantageous "good" compromise between competing functional limitations, or as a historical maladaptive relic of the convoluted path of organ evolution and transformation. Vision is an important adaptation in higher vertebrates. A third view of the "inverted" vertebrate eye

2178-417: A protozoan; many species of bacteria are digested by the protozoan as it undergoes cystic growth. Retina The retina (from Latin rete  'net'; pl.   retinae or retinas ) is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs . The optics of the eye create a focused two-dimensional image of the visual world on

2299-578: A result, a pregnant woman might test negative during the active phase of T. gondii infection leading to undetected and therefore untreated congenital toxoplasmosis. Also, the test may not detect T. gondii infections in immunocompromised patients because the titers of specific anti- Toxoplasma IgG or IgM may not rise in this type of patient. Many PCR-based techniques have been developed to diagnose toxoplasmosis using clinical specimens that include amniotic fluid, blood , cerebrospinal fluid , and tissue biopsy . The most sensitive PCR-based technique

2420-461: A result, the useful lifetime of photoreceptors in invertebrates is much shorter than in vertebrates. Having easily replaced stalk eyes (some lobsters) or retinae (some spiders, such as Deinopis ) rarely occurs. The cephalopod retina does not originate as an outgrowth of the brain, as the vertebrate one does. This difference suggests that vertebrate and cephalopod eyes are not homologous , but have evolved separately. From an evolutionary perspective,

2541-456: A week or two of infection, peak within one to two months, then decline at various rates. Toxoplasma IgG antibodies generally persist for life, and therefore may be present in the bloodstream as a result of either current or previous infection. To some extent, acute toxoplasmosis infections can be differentiated from chronic infections using an IgG avidity test, which is a variation on the ELISA. In

SECTION 20

#1732875832608

2662-429: Is nested PCR , followed by hybridization of PCR products. The major downside to these techniques is that they are time-consuming and do not provide quantitative data. Real-time PCR is useful in pathogen detection, gene expression and regulation, and allelic discrimination. This PCR technique utilizes the 5' nuclease activity of Taq DNA polymerase to cleave a nonextendible, fluorescence-labeled hybridization probe during

2783-528: Is a lack of one or more of the cone subtypes that causes individuals to have deficiencies in colour vision or various kinds of colour blindness . These individuals are not blind to objects of a particular colour, but are unable to distinguish between colours that can be distinguished by people with normal vision. Humans have this trichromatic vision , while most other mammals lack cones with red sensitive pigment and therefore have poorer dichromatic colour vision. However, some animals have four spectral subtypes, e.g.

2904-413: Is a resting or dormant stage of a microorganism , that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. Many groups of single-celled, microscopic organisms, or microbes, possess the ability to enter this dormant state. Encystment, the process of cyst formation, can function as

3025-434: Is about 6 by 2   μm and bow-shaped, with the nucleus being one-third of its size. It can be identified by electron microscopy or by Giemsa staining tissue where the cytoplasm shows blue, the nucleus red. In its lifecycle, T. gondii adopts several forms. Tachyzoites are responsible for acute infection; they divide rapidly and spread through the tissues of the body. Tachyzoites are also known as "tachyzoic merozoites",

3146-417: Is also available. Changes in retinal blood circulation are seen with aging and exposure to air pollution, and may indicate cardiovascular diseases such as hypertension and atherosclerosis. Determining the equivalent width of arterioles and venules near the optic disc is also a widely used technique to identify cardiovascular risks. The retina translates an optical image into neural impulses starting with

3267-537: Is called mesopic vision . At mesopic light levels, both the rods and cones are actively contributing pattern information. What contribution the rod information makes to pattern vision under these circumstances is unclear. The response of cones to various wavelengths of light is called their spectral sensitivity. In normal human vision, the spectral sensitivity of a cone falls into one of three subtypes, often called blue, green, and red, but more accurately known as short, medium, and long wavelength-sensitive cone subtypes. It

3388-404: Is distinct from other types of microbial cysts in that the heterocysts are often produced in a repeating pattern within a filament composed of several vegetative cells, and once formed, heterocysts cannot return to a vegetative state. Protists, especially protozoan parasites, are often exposed to very harsh conditions at various stages in their life cycle. For example, Entamoeba histolytica ,

3509-464: Is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity. When thus excited by light, the photoceptor sends a proportional response synaptically to bipolar cells which in turn signal

3630-427: Is important for entrainment of circadian rhythms and reflexive responses such as the pupillary light reflex . Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent to various visual centres of the brain through the fibres of the optic nerve . Neural signals from the rods and cones undergo processing by other neurons, whose output takes

3751-403: Is most enhanced. The choroid supplies about 75% of these nutrients to the retina and the retinal vasculature only 25%. When light strikes 11-cis-retinal (in the disks in the rods and cones), 11-cis-retinal changes to all-trans-retinal which then triggers changes in the opsins. Now, the outer segments do not regenerate the retinal back into the cis- form once it has been changed by light. Instead

Toxoplasmosis - Misplaced Pages Continue

3872-438: Is not direct. Since about 150 million receptors and only 1 million optic nerve fibres exist, convergence and thus mixing of signals must occur. Moreover, the horizontal action of the horizontal and amacrine cells can allow one area of the retina to control another (e.g. one stimulus inhibiting another). This inhibition is key to lessening the sum of messages sent to the higher regions of the brain. In some lower vertebrates (e.g.

3993-423: Is partly transparent, and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors, light scattering does occur. Some vertebrates, including humans, have an area of the central retina adapted for high-acuity vision. This area, termed the fovea centralis , is avascular (does not have blood vessels), and has minimal neural tissue in front of

4114-425: Is recommended in the first and early second trimesters while pyrimethamine/sulfadiazine and leucovorin is recommended in the late second and third trimesters. In people with latent toxoplasmosis, the cysts are immune to these treatments, as the antibiotics do not reach the bradyzoites in sufficient concentration. The medications prescribed for latent toxoplasmosis are: Microbial cyst A microbial cyst

4235-525: Is that it combines two benefits - the maintenance of the photoreceptors mentioned above, and the reduction in light intensity necessary to avoid blinding the photoreceptors, which are based on the extremely sensitive eyes of the ancestors of modern hagfish (fish that live in very deep, dark water). A recent study on the evolutionary purpose for the inverted retina structure from the APS (American Physical Society) says that "The directional of glial cells helps increase

4356-417: Is the drug of choice to prevent toxoplasmosis, but not for treating active disease. A 2012 study shows a promising new way to treat the active and latent form of this disease using two endochin-like quinolones . The medications prescribed for acute toxoplasmosis are the following: (other antibiotics, such as minocycline , have seen some use as a salvage therapy ). If infected during pregnancy, spiramycin

4477-505: Is typically by testing blood for antibodies or by testing the amniotic fluid in a pregnant patient for the parasite's DNA . Prevention is by properly preparing and cooking food. Pregnant women are also recommended not to clean cat litter boxes or, if they must, to wear gloves and wash their hands afterwards. Treatment of otherwise healthy people is usually not needed. During pregnancy, spiramycin or pyrimethamine / sulfadiazine and folinic acid may be used for treatment. Up to half of

4598-613: The Sabin–Feldman dye test (DT), the indirect hemagglutination assay , the indirect fluorescent antibody assay (IFA) , the direct agglutination test , the latex agglutination test (LAT), the enzyme-linked immunosorbent assay (ELISA) , and the immunosorbent agglutination assay test (IAAT). The most commonly used tests to measure IgG antibody are the DT, the ELISA, the IFA, and the modified direct agglutination test. IgG antibodies usually appear within

4719-408: The ophthalmic artery bifurcates and supplies the retina via two distinct vascular networks: the choroidal network, which supplies the choroid and the outer retina, and the retinal network, which supplies the retina's inner layer. Although the inverted retina of vertebrates appears counter-intuitive, it is necessary for the proper functioning of the retina. The photoreceptor layer must be embedded in

4840-425: The outer plexiform layer and the inner plexiform layer . In the outer neuropil layer, the rods and cones connect to the vertically running bipolar cells , and the horizontally oriented horizontal cells connect to ganglion cells. The central retina predominantly contains cones, while the peripheral retina predominantly contains rods. In total, the retina has about seven million cones and a hundred million rods. At

4961-412: The photosensitive ganglion cells ; and transmission along the optic nerve. At each synaptic stage, horizontal and amacrine cells also are laterally connected. The optic nerve is a central tract of many axons of ganglion cells connecting primarily to the lateral geniculate body , a visual relay station in the diencephalon (the rear of the forebrain). It also projects to the superior colliculus ,

Toxoplasmosis - Misplaced Pages Continue

5082-787: The pigeon ), control of messages is "centrifugal" – that is, one layer can control another, or higher regions of the brain can drive the retinal nerve cells, but in primates, this does not occur. Using optical coherence tomography (OCT), 18 layers can be identified in the retina. The layers and anatomical correlation are: From innermost to outermost, the layers identifiable by OCT are as follows: on OCT anatomical boundaries? references (unclear if it can be observed on OCT) b) Müller cell nuclei (obliquely orientated fibres; not present in mid-peripheral or peripheral retina) Poorly distinguishable from RPE. Previously: "cone outer segment tips line" (COST) homogenous region of variable reflectivity Retinal development begins with

5203-403: The receptive field of the cell. The receptive fields of retinal ganglion cells comprise a central, approximately circular area, where light has one effect on the firing of the cell, and an annular surround, where light has the opposite effect. In ON cells, an increment in light intensity in the centre of the receptive field causes the firing rate to increase. In OFF cells, it makes it decrease. In

5324-425: The retinal ganglion cells . The photoreceptors are also cross-linked by horizontal cells and amacrine cells , which modify the synaptic signal before it reaches the ganglion cells, the neural signals being intermixed and combined. Of the retina's nerve cells, only the retinal ganglion cells and few amacrine cells create action potentials . In the retinal ganglion cells there are two types of response, depending on

5445-551: The retinas , alveolar lining of the lungs (where an acute infection may mimic a Pneumocystis jirovecii infection), heart, skeletal muscle, and the central nervous system (CNS), including the brain. Cysts form in the CNS ( brain tissue ) upon infection with T. gondii and persist for the lifetime of the host. Most infants who are infected while in the womb have no symptoms at birth, but may develop symptoms later in life. Reviews of serological studies have estimated that 30–50% of

5566-431: The suprachiasmatic nucleus , and the nucleus of the optic tract . It passes through the other layers, creating the optic disc in primates. Additional structures, not directly associated with vision, are found as outgrowths of the retina in some vertebrate groups. In birds , the pecten is a vascular structure of complex shape that projects from the retina into the vitreous humour ; it supplies oxygen and nutrients to

5687-597: The Animalcules I have before described out of the water, not leaving the quantity of a grain of sand adjoining to them, in order to see whether when all the water about them was evaporated and they were exposed to the air their bodies would burst, as I had often seen in other Animalcules. But now I found that when almost all the water was evaporated, so that the creature could no longer be covered with water, nor move itself as usual, it then contracted itself into an oval figure, and in that state it remained, nor could I perceive that

5808-454: The IgG antibodies and disappear faster than IgG antibodies after recovery. In most cases, T. gondii -specific IgM antibodies can first be detected approximately a week after acquiring primary infection and decrease within one to six months; 25% of those infected are negative for T. gondii -specific IgM within seven months. However, IgM may be detectable months or years after infection, during

5929-520: The N-T axis is coordinated by expression of the forkhead transcription factors FOXD1 and FOXG1 . Additional gradients are formed within the retina. This spatial distribution may aid in proper targeting of RGC axons that function to establish the retinotopic map. The retina is stratified into distinct layers, each containing specific cell types or cellular compartments that have metabolisms with different nutritional requirements. To satisfy these requirements,

6050-510: The absence of obvious symptoms, hosts easily become infected with T. gondii and develop toxoplasmosis without knowing it. Although mild, flu-like symptoms occasionally occur during the first few weeks following exposure, infection with T. gondii produces no readily observable symptoms in healthy human adults. In most immunocompetent people, the infection enters a latent phase, during which only bradyzoites ( in tissue cysts ) are present; these tissue cysts and even lesions can occur in

6171-488: The absorption of stray light falling on the pecten. This is considered to enhance metabolic rate of the pecten, thereby exporting more nutritive molecules to meet the stringent energy requirements of the retina during long periods of exposure to light. The bifurcations and other physical characteristics of the inner retinal vascular network are known to vary among individuals, and these individual variances have been used for biometric identification and for early detection of

SECTION 50

#1732875832608

6292-409: The acquired form of the disease, including roseola and erythema multiforme-like eruptions, prurigo -like nodules, urticaria , and maculopapular lesions . Newborns may have punctate macules, ecchymoses , or "blueberry muffin" lesions. Diagnosis of cutaneous toxoplasmosis is based on the tachyzoite form of T. gondii being found in the epidermis . It is found in all levels of the epidermis,

6413-440: The arguments made by Pouchet, with notable dissension from the main author who blamed his framing of the issue in the report on fear of religious retribution. Despite the attempt by Doyere and Pouchet to conclude debate on the topic of resurrection, investigations continued. In 1872, Wilhelm Preyer introduced the term ‘ anabiosis ’ (return to life) to describe the revitalization of viable, lifeless organisms to an active state. This

6534-439: The baby is born has been suggested to be effective because it may improve food, personal and pet hygiene. More research is needed to find whether antenatal education can reduce congenital toxoplasmosis. For pregnant women with negative antibody titers, indicating no previous exposure to T. gondii , serology testing as frequent as monthly is advisable as treatment during pregnancy for those women exposed to T. gondii for

6655-481: The birth rate is around 51% boys, but people infected with T. gondii had up to a 72% chance of a boy. Toxoplasmosis in humans is diagnosed through biological, serological, histological, or molecular methods, or by some combination of the above. Toxoplasmosis can be difficult to distinguish from primary central nervous system lymphoma . Its symptoms mimic several other infectious diseases, so clinical signs are non-specific and are not sufficiently characteristic for

6776-579: The body. Since the parasite can change the host's immune response, it may also have an effect, positive or negative, on the immune response to other pathogenic threats. This includes, but is not limited to, the responses to infections by Helicobacter felis , Leishmania major , or other parasites, such as Nippostrongylus brasiliensis . Toxoplasmosis is generally transmitted through the mouth when Toxoplasma gondii oocysts or tissue cysts are accidentally eaten. Congenital transmittance from mother to fetus can also occur. Transmission may also occur during

6897-485: The brain ( encephalitis ) or the eyes ( necrotizing retinochoroiditis ). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns. The toxoplasmic trophozoites causing acute toxoplasmosis are referred to as tachyzoites , and are typically found in various tissues and body fluids, but rarely in blood or cerebrospinal fluid. Swollen lymph nodes are commonly found in

7018-454: The brain, the retina is isolated from the vascular system by the blood–brain barrier . The retina is the part of the body with the greatest continuous energy demand. The vertebrate retina is inverted in the sense that the light-sensing cells are in the back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the photosensitive sections of the rods and cones. The ganglion cells, whose axons form

7139-411: The centre of the macula is the foveal pit where the cones are narrow and long, and arranged in a hexagonal mosaic , the most dense, in contradistinction to the much fatter cones located more peripherally in the retina. At the foveal pit, the other retinal layers are displaced, before building up along the foveal slope until the rim of the fovea, or parafovea , is reached, which is the thickest portion of

7260-458: The chemical composition of certain protozoan cyst walls may play a role in their dispersal. The sialyl groups present in the cyst wall of Entamoeba histolytica confer a net negative charge to the cyst which prevents its attachment to the intestinal wall thus causing its elimination in the feces. Other protozoan intestinal parasites like Giardia lamblia and Cryptosporidium also produce cysts as part of their life cycle (see oocyst ). Due to

7381-468: The chronic phase, and false positives for acute infection are possible. The most commonly used tests for the measurement of IgM antibody are double-sandwich IgM-ELISA , the IFA test , and the immunosorbent agglutination assay (IgM-ISAGA). Commercial test kits often have low specificity, and the reported results are frequently misinterpreted. In 2021, twenty commercial anti- Toxoplasma IgG assays were evaluated in

SECTION 60

#1732875832608

7502-483: The clarity of human vision. But we also noticed something rather curious: the colours that best passed through the glial cells were green to red, which the eye needs most for daytime vision. The eye usually receives too much blue—and thus has fewer blue-sensitive cones. Further computer simulations showed that green and red are concentrated five to ten times more by the glial cells, and into their respective cones, than blue light. Instead, excess blue light gets scattered to

7623-422: The correspondence between X and Y cells (in the cat retina) and P and M cells (in the primate retina) is not as simple as it once seemed. In the transfer of visual signals to the brain, the visual pathway , the retina is vertically divided in two, a temporal (nearer to the temple) half and a nasal (nearer to the nose) half. The axons from the nasal half cross the brain at the optic chiasma to join with axons from

7744-573: The debate surrounding the theory of spontaneous generation of life, leading two highly involved scientists on either side of the issue to call upon the Biological Society of France for an independent review of their opposing conclusions on the matter. Doyere, who believed rotifers could be desiccated and revitalized, and Pouchet, who believed they could not, allowed independent observers of various scientific backgrounds to observe and attempt to replicate their findings. The resulting report leaned toward

7865-412: The diagnosis of congenital toxoplasmosis include: prenatal diagnosis based on testing of amniotic fluid and ultrasound examinations; neonatal diagnosis based on molecular testing of placenta and cord blood and comparative mother-child serologic tests and a clinical examination at birth; and early childhood diagnosis based on neurologic and ophthalmologic examinations and a serologic survey during

7986-530: The disease reactivating in their system due to the immunosuppression occurring during solid organ transplant. Recipients of hematogenous stem cell transplants may experience higher risk of infection due to longer periods of immunosuppression. Heart and lung transplants provide the highest risk for toxoplasmosis infection due to the striated muscle making up the heart, which can contain cysts, and risks for other organs and tissues vary widely. Risk of transmission can be reduced by screening donors and recipients prior to

8107-651: The encysted microbe reaches an environment favorable to its growth and survival, the cyst wall breaks down by a process known as excystation . Environmental conditions that may trigger encystment include, but are not limited to: lack of nutrients or oxygen, extreme temperatures, desiccation , adverse pH, and presence of toxic chemicals which are not conducive for the growth of the microbe. The idea that microbes could temporarily assume an alternate state of being to withstand changes in environmental conditions began with Antonie van Leeuwenhoek’s 1702 study on Animalcules , currently known as rotifers : “'I have often placed

8228-612: The endoplasmic reticulum also frequently indicate a ciliate is undergoing encystment. The composition of the cyst wall is variable in different organisms. In bacteria (for instance, Azotobacter sp. ), encystment occurs by changes in the cell wall ; the cytoplasm contracts and the cell wall thickens. Various members of the Azotobacteraceae family have been shown to survive in an encysted form for up to 24 years. The extremophile Rhodospirillum centenum , an anoxygenic, photosynthetic, nitrogen-fixing bacterium that grows in hot springs

8349-525: The establishment of the eye fields mediated by the SHH and SIX3 proteins, with subsequent development of the optic vesicles regulated by the PAX6 and LHX2 proteins. The role of Pax6 in eye development was elegantly demonstrated by Walter Gehring and colleagues, who showed that ectopic expression of Pax6 can lead to eye formation on Drosophila antennae, wings, and legs. The optic vesicle gives rise to three structures:

8470-875: The extension phase of PCR. A second fluorescent dye, e.g., 6-carboxy-tetramethyl-rhodamine, quenches the fluorescence of the intact probe. The nuclease cleavage of the hybridization probe during the PCR releases the effect of quenching resulting in an increase of fluorescence proportional to the amount of PCR product, which can be monitored by a sequence detector. Lymph nodes affected by Toxoplasma have characteristic changes, including poorly demarcated reactive germinal centers , clusters of monocytoid B cells, and scattered epithelioid histiocytes . The classic triad of congenital toxoplasmosis includes: chorioretinitis , hydrocephalus , and intracranial arteriosclerosis . Other consequences include sensorineural deafness, seizures, and intellectual disability. Congenital toxoplasmosis may also impact

8591-407: The eye, and may also aid in vision. Reptiles have a similar, but much simpler, structure. In adult humans, the entire retina is about 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods. The optic disc, a part of the retina sometimes called "the blind spot" because it lacks photoreceptors, is located at the optic papilla , where

8712-456: The fetus is at particular risk. A simple blood draw at the first prenatal doctor visit can determine whether or not a woman has had previous exposure and therefore whether or not she is at risk. A positive antibody titer indicates previous exposure and immunity, and largely ensures the unborn fetus' safety. Not much evidence exists around the effect of education before pregnancy to prevent congenital toxoplasmosis. However educating parents before

8833-643: The first response to infection, toxoplasma-specific IgG has a low affinity for the toxoplasma antigen; in the following weeks and month, IgG affinity for the antigen increases. Based on the IgG avidity test, if the IgG in the infected individual has a high affinity, it means that the infection began three to five months before testing. This is particularly useful in congenital infection, where pregnancy status and gestational age at time of infection determines treatment. In contrast to IgG, IgM antibodies can be used to detect acute infection but generally not chronic infection. The IgM antibodies appear sooner after infection than

8954-458: The first time dramatically decreases the risk of passing the parasite to the fetus. Since a baby's immune system does not develop fully for the first year of life, and the resilient cysts that form throughout the body are very difficult to eradicate with antiprotozoans, an infection can be very serious in the young. Despite these risks, pregnant women are not routinely screened for toxoplasmosis in most countries, for reasons of cost-effectiveness and

9075-464: The first year of life. During pregnancy, serological testing is recommended at three week intervals. Even though diagnosis of toxoplasmosis heavily relies on serological detection of specific anti- Toxoplasma immunoglobulin, serological testing has limitations. For example, it may fail to detect the active phase of T. gondii infection because the specific anti- Toxoplasma IgG or IgM may not be produced until after several weeks of infection. As

9196-450: The form of action potentials in retinal ganglion cells whose axons form the optic nerve. In vertebrate embryonic development , the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon ; thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue. It is the only part of the CNS that can be visualized noninvasively . Like most of

9317-453: The global population has been exposed to and may be chronically infected with latent toxoplasmosis, although infection rates differ significantly from country to country. This latent state of infection has recently been associated with numerous disease burdens , neural alterations, and subtle sex-dependent behavioral changes in immunocompetent humans, as well as an increased risk of motor vehicle collisions. While rare, skin lesions may occur in

9438-551: The hard outer shell of the cyst, Cryptosporidium and Giardia are resistant to common disinfectants used by water treatment facilities such as chlorine. In some protozoans, the unicellular organism multiplies during or after encystment and releases multiple trophozoites upon excystation. Many additional species of protists have been shown to exhibit encystment when confronted with unfavorable environmental conditions. Rotifers also produce diapause cysts, which are different from quiescent (environmentally triggered) cysts in that

9559-712: The high number of false positives generated; Portugal , France , Austria , Uruguay , and Italy are notable exceptions, and some regional screening programmes operate in Germany , Switzerland and Belgium . As invasive prenatal testing incurs some risk to the fetus (18.5 pregnancy losses per toxoplasmosis case prevented), postnatal or neonatal screening is preferred. The exceptions are cases where fetal abnormalities are noted, and thus screening can be targeted. Pregnant women should avoid handling raw meat , drinking raw milk (especially goat milk) and be advised to not eat raw or undercooked meat regardless of type. Because of

9680-406: The host's immune response, reducing the host's immune response, and enhancing the parasite's reproductive advantage. Once it infects a normal host cell, it resists damage caused by the host's immune system, and changes the host's immune processes. As it forces its way into the host cell, the parasite forms a parasitophorous vacuole (PV) membrane from the membrane of the host cell. The PV encapsulates

9801-433: The infected host cells to persist and replicate. One method of apoptosis resistance is by disrupting pro-apoptosis effector proteins, such as BAX and BAK . To disrupt these proteins, T. gondii causes conformational changes to the proteins, which prevent the proteins from being transported to various cellular compartments where they initiate apoptosis events. T. gondii does not, however, cause downregulation of

9922-476: The lack of understanding of genetic mechanisms and additional defining characteristics, though they are generally thought to follow a different formation sequence than endospores. Indicators of cyst formation in ciliated protists include varying degrees of ciliature resorption, with some ciliates losing both cilia and the membranous structures supporting them while others maintain kinetosomes and/or microtubular structures. De novo synthesis of cyst wall precursors in

10043-578: The life cycle of ciliates and other microbes. The realization that no one category of microscopic organism ‘owns’ the ability to form metabolically dormant cysts necessitates the term ‘microbial cyst’ to describe the physical object as it exists in all its forms. Also important in the generation of the term, is the delineation of endospores and microbial cysts as different forms of cryptobiosis or dormancy. Endospores exhibit more extreme isolation from their environment in terms of cell wall thickness, impermeability to substrates, and presence of dipicolinic acid ,

10164-437: The moisture evaporated from its body, for it preserved its oval and round shape, unhurt." Leeuwenhoek later continued his work with rotifers to discover that when he returned the dried bodies to their preferred aquatic conditions, they resumed their original shape and began swimming again. These observations did not gain traction with the general microbiological community of the time, and the phenomena as Leeuwenhoek observed it

10285-555: The neck or under the chin, followed by the armpits and the groin. Swelling may occur at different times after the initial infection, persist, and recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children, multiple sites may be more common. Enlarged lymph nodes will resolve within 1–2 months in 60% of cases. However, a quarter of those affected take 2–4 months to return to normal, and 8% take 4–6 months. A substantial number (6%) do not return to normal until much later. Due to

10406-503: The neural retina, the retinal pigmented epithelium, and the optic stalk. The neural retina contains the retinal progenitor cells (RPCs) that give rise to the seven cell types of the retina. Differentiation begins with the retinal ganglion cells and concludes with production of the Muller glia. Although each cell type differentiates from the RPCs in a sequential order, there is considerable overlap in

10527-427: The obvious relationship between Toxoplasma and cats it is also often advised to avoid exposure to cat feces, and refrain from gardening (cat feces are common in garden soil) or at least wear gloves when so engaged. Most cats are not actively shedding oocysts , since they get infected in the first six months of their life, when they shed oocysts for a short period of time (1–2 weeks). However, these oocysts get buried in

10648-517: The onset of disease. The mapping of vascular bifurcations is one of the basic steps in biometric identification. Results of such analyses of retinal blood vessel structure can be evaluated against the ground truth data of vascular bifurcations of retinal fundus images that are obtained from the DRIVE dataset. In addition, the classes of vessels of the DRIVE dataset have also been identified, and an automated method for accurate extraction of these bifurcations

10769-445: The optic nerve are devoted to the fovea. The resolution limit of the fovea has been determined to be around 10,000 points. The information capacity is estimated at 500,000 bits per second (for more information on bits, see information theory ) without colour or around 600,000 bits per second including colour. When the retina sends neural impulses representing an image to the brain, it spatially encodes (compresses) those impulses to fit

10890-421: The optic nerve, are at the front of the retina; therefore, the optic nerve must cross through the retina en route to the brain. No photoreceptors are in this region, giving rise to the blind spot . In contrast, in the cephalopod retina, the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot. Although the overlying neural tissue

11011-478: The optic-nerve fibres leave the eye. It appears as an oval white area of 3 mm . Temporal (in the direction of the temples) to this disc is the macula , at whose centre is the fovea , a pit that is responsible for sharp central vision, but is actually less sensitive to light because of its lack of rods. Human and non-human primates possess one fovea, as opposed to certain bird species, such as hawks, that are bifoviate, and dogs and cats, that possess no fovea, but

11132-475: The parasite, and is both resistant to the activity of the endolysosomal system, and can take control of the host's mitochondria and endoplasmic reticulum . When first invading the cell, the parasite releases ROP proteins from the bulb of the rhoptry organelle. These proteins translocate to the nucleus and the surface of the PV membrane where they can activate STAT pathways to modulate the expression of cytokines at

11253-747: The patterned excitation of the colour-sensitive pigments of its rods and cones, the retina's photoreceptor cells . The excitation is processed by the neural system and various parts of the brain working in parallel to form a representation of the external environment in the brain. The cones respond to bright light and mediate high-resolution colour vision during daylight illumination (also called photopic vision ). The rod responses are saturated at daylight levels and do not contribute to pattern vision. However, rods do respond to dim light and mediate lower-resolution, monochromatic vision under very low levels of illumination (called scotopic vision ). The illumination in most office settings falls between these two levels and

11374-499: The photoreceptors, thereby minimizing light scattering. The cephalopods have a non-inverted retina, which is comparable in resolving power to the eyes of many vertebrates. Squid eyes do not have an analog of the vertebrate retinal pigment epithelium (RPE). Although their photoreceptors contain a protein, retinochrome, that recycles retinal and replicates one of the functions of the vertebrate RPE, cephalopod photoreceptors are likely not maintained as well as in vertebrates, and that as

11495-434: The pro-apoptosis effector proteins. T. gondii also has the ability to initiate autophagy of the host's cells. This leads to a decrease in healthy, uninfected cells, and consequently fewer host cells to attack the infected cells. Research by Wang et al finds that infected cells lead to higher levels of autophagosomes in normal and infected cells. Their research reveals that T. gondii causes host cell autophagy using

11616-435: The process of their formation begins before environmental conditions have deteriorated to unfavorable levels and the dormant state may extend past the restoration of ideal conditions for microbial life. Food limited females of some Synchaeta pectinata strains produce unfertilized diapausing eggs with a thicker shell. Fertilized diapausing eggs can be produced in both food limited and non-food limited conditions, indicative of

11737-458: The resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal . This causes the receptor to activate multiple G-proteins . This in turn causes the Ga-subunit of the protein to activate a phosphodiesterase (PDE6), which degrades cGMP, resulting in the closing of Na+ cyclic nucleotide-gated ion channels (CNGs). Thus the cell

11858-414: The retina are the photoreceptor cells , which are of two types: rods and cones . Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins , as well as high-acuity vision used for tasks such as reading. A third type of light-sensing cell, the photosensitive ganglion cell ,

11979-470: The retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception . The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera . The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in

12100-450: The retina. The macula has a yellow pigmentation, from screening pigments, and is known as the macula lutea. The area directly surrounding the fovea has the highest density of rods converging on single bipolar cells. Since its cones have a much lesser convergence of signals, the fovea allows for the sharpest vision the eye can attain. Though the rod and cones are a mosaic of sorts, transmission from receptors, to bipolars, to ganglion cells

12221-511: The retinal is pumped out to the surrounding RPE where it is regenerated and transported back into the outer segments of the photoreceptors. This recycling function of the RPE protects the photoreceptors against photo-oxidative damage and allows the photoreceptor cells to have decades-long useful lives. The bird retina is devoid of blood vessels, perhaps to give unobscured passage of light for forming images, thus giving better resolution. It is, therefore,

12342-490: The retinal pigment epithelium (RPE), which performs at least seven vital functions, one of the most obvious being to supply oxygen and other necessary nutrients needed for the photoreceptors to function. The energy requirements of the retina are even greater than that of the brain. This is due to the additional energy needed to continuously renew the photoreceptor outer segments, of which 10% are shed daily. Energy demands are greatest during dark adaptation when its sensitivity

12463-500: The rods and cones. Light is absorbed by the retinal pigment epithelium or the choroid (both of which are opaque). The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon). Between the ganglion-cell layer and the rods and cones are two layers of neuropils , where synaptic contacts are made. The neuropil layers are

12584-477: The soil, sporulate and remain infectious for periods ranging from several months to more than a year. Numerous studies have shown living in a household with a cat is not a significant risk factor for T. gondii infection, though living with several kittens has some significance. In 2006, a Czech research team discovered women with high levels of toxoplasmosis antibodies were significantly more likely to give birth to baby boys than baby girls. In most populations,

12705-494: The solid organ transplant process or hematogenous stem cell transplants. Oral transmission may occur through: Cats excrete the pathogen in their feces for a number of weeks after contracting the disease, generally by eating an infected intermediate host that could include mammals (like rodents) or birds. Oocyst shedding usually starts from the third day after ingestion of infected intermediate hosts, and may continue for weeks. The oocysts are not infective when excreted. After about

12826-418: The surrounding rods. This optimization is such that color vision during the day is enhanced, while night-time vision suffers very little". The vertebrate retina has 10 distinct layers. From closest to farthest from the vitreous body: These layers can be grouped into four main processing stages—photoreception; transmission to bipolar cells ; transmission to ganglion cells , which also contain photoreceptors,

12947-450: The temporal half of the other eye before passing into the lateral geniculate body . Although there are more than 130 million retinal receptors, there are only approximately 1.2 million fibres (axons) in the optic nerve. So, a large amount of pre-processing is performed within the retina. The fovea produces the most accurate information. Despite occupying about 0.01% of the visual field (less than 2° of visual angle ), about 10% of axons in

13068-406: The term ‘ cryptobiosis ’ (latent life) to describe: “...the state of an organism when it shows no visible signs of life and when its metabolic activity becomes hardly measurable, or comes reversibly to a standstill.” As microbial research began to gain popularity exponentially, details about ciliated protist physiology and cyst formation led to increased curiosity about the role of encystment in

13189-430: The timing of when individual cell types differentiate. The cues that determine a RPC daughter cell fate are coded by multiple transcription factor families including the bHLH and homeodomain factors. In addition to guiding cell fate determination, cues exist in the retina to determine the dorsal-ventral (D-V) and nasal-temporal (N-T) axes. The D-V axis is established by a ventral to dorsal gradient of VAX2 , whereas

13310-491: The tissues for the lifespan of the host. In a healthy host, if some bradyzoites convert back into active tachyzoites, the immune system will quickly destroy them. However, in immunocompromised individuals, or in fetuses, which lack a developed immune system, the tachyzoites can run rampant and cause significant neurological damage. The parasite's survival is dependent on a balance between host survival and parasite proliferation. T. gondii achieves this balance by manipulating

13431-588: The transcriptional level, bind and inactivate PV membrane destroying IRG proteins, among other possible effects. Additionally, certain strains of T. gondii can secrete a protein known as GRA15, activating the NF-κB pathway, which upregulates the pro-inflammatory cytokine IL-12 in the early immune response, possibly leading to the parasite's latent phase. The parasite's ability to secrete these proteins depends on its genotype and affects its virulence. The parasite also influences an anti-apoptotic mechanism, allowing

13552-469: The transplant procedure and providing treatment. Congenital toxoplasmosis is a specific form of toxoplasmosis in which an unborn fetus is infected via the placenta . Congenital toxoplasmosis is associated with fetal death and miscarriage, and in infants, it is associated with hydrocephalus, cerebral calcifications and chorioretinitis , leading to encephalopathy and possibly blindness. If a woman receives her first exposure to T. gondii while pregnant,

13673-476: The trout adds an ultraviolet subgroup to short, medium, and long subtypes that are similar to humans. Some fish are sensitive to the polarization of light as well. In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment . Inside the cell the normal levels of cyclic guanosine monophosphate (cGMP) keep the Na+ channel open, and thus in

13794-436: The unique ribbon synapse . The optic nerve carries the ganglion-cell axons to the brain, and the blood vessels that supply the retina. The ganglion cells lie innermost in the eye while the photoreceptive cells lie beyond. Because of this counter-intuitive arrangement, light must first pass through and around the ganglion cells and through the thickness of the retina, (including its capillary vessels, not shown) before reaching

13915-479: The world's population is infected by T. gondii , but have no symptoms. In the United States, approximately 11% of people have been infected, while in some areas of the world this is more than 60%. Approximately 200,000 cases of congenital toxoplasmosis occur a year. Charles Nicolle and Louis Manceaux first described the organism in 1908. In 1941, transmission during pregnancy from a pregnant woman to her baby

14036-407: Was confirmed. There is tentative evidence that otherwise asymptomatic infection may affect people's behavior. Infection has three stages: Acute toxoplasmosis is often asymptomatic in healthy adults. However, symptoms may manifest and are often influenza -like: swollen lymph nodes , headaches, fever, and fatigue, or muscle aches and pains that last for a month or more. It is rare for a human with

14157-482: Was found to form cysts in response to desiccation as well. Bacteria do not always form a single cyst. Varieties of cysts formation events are known. Rhodospirillum centenum can change the number of cysts per cell, usually ranging from four to ten cells per cyst depending on the environment. Some species of filamentous cyanobacteria have been known to form heterocysts to escape levels of oxygen concentration detrimental to their nitrogen fixing processes. This process

14278-432: Was generally high, ranging from 91.3% to 100%; and higher than 99% for most EIA assays. The positive predictive value (PPV) was not a discriminant indicator among methods, whereas significant disparities (87.5–100%) were reported among negative predictive values (NPV), a key-parameter assessing the ability to definitively rule out a Toxoplasma infection in patients at-risk for opportunistic infections. Recommendations for

14399-484: Was never given a name. In 1743, John Turberville Needham observed the revival of the encysted larval stage of the wheat parasite, Anguillulina tritici and later published these findings in New Microscopal Discoveries (1745). Several others repeated and expanded upon this work, informally referring to their studies on the “phenomenon of reviviscence.” In the late 1850s, reviviscence became embroiled in

14520-419: Was previously believed that encystment only served a purpose for the organism itself, it has been found that protozoan cysts have a harboring effect. Common pathogenic bacteria can also be found taking refuge in the cyst of free-living protozoa. Survival times for bacteria in these cysts range from a few days to a few months in harsh environments. Not all bacteria are guaranteed to survive in the cyst formation of

14641-430: Was quickly followed by Schmidt’s 1948 proposal of the term ‘abiosis,’ leading to some confusion between terms describing the beginning of life from non-living elements, viable lifelessness, and nonliving components that are necessary for life. As part of his 1959 review of Leeuwenhoek’s original findings and the evolution of the science surrounding microbial cysts and other forms of metabolic suspension, D. Keilin proposed

#607392