Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most warm-blooded animals, including humans, but the primary host is the felid (cat) family. Animals are infected by eating infected meat, by ingestion of faeces of a cat that has itself recently been infected, or by transmission from mother to fetus. Cats have been shown as a major reservoir of this infection.
Up to one third of the world's population is estimated to carry a Toxoplasma infection.The Centers for Disease Control and Prevention notes that overall seroprevalence in the United States as determined with specimens collected by the third National Health and Nutritional Assessment Survey (NHANES III) between 1988 and 1994 was found to be 22.5%, with seroprevalence among women of childbearing age (15 to 44 years) of 15%.People with a weakened immune system, such as those infected with HIV, and fetuses, may become seriously ill, and it can occasionally be fatal. The parasite can cause encephalitis (inflammation of the brain) and neurologic diseases and can affect the heart, liver, and eyes (chorioretinitis).
The protozoan was first discovered by Nicolle & Manceaux, who in 1908 isolated it from the African rodent Ctenodactylus gundi, then in 1909 differentiated the disease from Leishmania and named it Toxoplasmosis gondii. The first recorded congenital case was not until 1923, and the first adult case not until 1940. In 1948, a serological dye test was created by Sabin & Feldman, which is now the standard basis for diagnostic tests.
Transmission
Ingestion of raw or partly cooked meat, especially pork, lamb, or venison containing Toxoplasma cysts. Infection prevalence in countries where undercooked meat is traditionally eaten, such as France, has been related to this transmission method. Oocysts may also be ingested during hand-to-mouth contact after handling undercooked meat, or from using knives, utensils, or cutting boards contaminated by raw meat. Ingestion of contaminated cat faeces. This can occur through hand-to-mouth contact following gardening, cleaning a cat's litter box, contact with children's sandpits, or touching anything that has come into contact with cat faeces.
Drinking water contaminated with Toxoplasma.
Transplacental infection in utero.
Receiving an infected organ transplant or blood transfusion, although this is extremely rare.
The cyst form of the parasite is extremely hardy, capable of surviving exposure to freezing down to −12 degrees Celsius (10 degrees Fahrenheit), moderate temperatures and chemical disinfectants such as bleach, and can survive in the environment for over a year. It is, however, susceptible to high temperatures—above 66 degrees Celsius (150 degrees Fahrenheit), and is thus killed by thorough cooking, and would be killed by 24 hours in a typical domestic freezer.
Cats excrete the pathogen in their faeces for a number of weeks after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic. Studies have shown that only about 2% of cats are shedding oocysts at any one time, and that oocyst shedding does not recur even after repeated exposure to the parasite. Although the pathogen has been detected on the fur of cats, it has not been found in an infectious form, and direct infection from handling cats is generally believed to be very rare.
Pregnancy precautions
Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta. A positive antibody titer indicates previous exposure and immunity and largely ensures the unborn baby's safety. A simple blood draw at the first pre-natal doctor visit can determine whether or not the woman has had previous exposure and therefore whether or not she is at risk. If a woman receives her first exposure to toxoplasmosis while pregnant, the baby is at particular risk. A woman with no previous exposure should avoid handling raw meat, exposure to cat feces, and gardening (cat feces are common in garden soil). Most cats are not actively shedding oocysts and so are not a danger, but the risk may be reduced further by having the litterbox emptied daily (oocysts require longer than a single day to become infective), and by having someone else empty the litterbox. However, while risks can be minimized, they cannot be eliminated. For pregnant women with negative antibody titer, indicating no previous exposure to T. gondii, as frequent as monthly serology testing is advisable as treatment during pregnancy for those women exposed to T. gondii for the first time decreases dramatically the risk of passing the parasite to the fetus.
Treatment is very important for recently infected pregnant women, to prevent infection of 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 anti-protozoans, an infection can be very serious in the young.
Transplacental transmission:(a) infection in 1st trimester - incidence of transplacental infection is low (15%) but disease in neonate is most severe. (b) infection in 3rd trimester - incidence of transplacental infection is high (65%) but infant is usually asymptomatic at birth.
Infection has two stages:
Acute
During acute toxoplasmosis, symptoms are often influenza-like: swollen lymph nodes, or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioning immune system may develop eye damage from toxoplasmosis. Young children and immunocompromised patients, 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 the brain or the eyes. Only a small percentage of infected newborn babies have serious eye or brain damage at birth.
Latent
Most patients who become infected with Toxoplasma gondii and develop toxoplasmosis do not know it. In most immunocompetent patients, the infection enters a latent phase, during which only bradyzoites are present, forming cysts in nervous and muscle tissue. Most infants who are infected while in the womb have no symptoms at birth but may develop symptoms later in life.
Acute
During acute toxoplasmosis, symptoms are often influenza-like: swollen lymph nodes, or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioning immune system may develop eye damage from toxoplasmosis. Young children and immunocompromised patients, 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 the brain or the eyes. Only a small percentage of infected newborn babies have serious eye or brain damage at birth.
Latent
Most patients who become infected with Toxoplasma gondii and develop toxoplasmosis do not know it. In most immunocompetent patients, the infection enters a latent phase, during which only bradyzoites are present, forming cysts in nervous and muscle tissue. Most infants who are infected while in the womb have no symptoms at birth but may develop symptoms later in life.
Treatment
Treatment is often only recommended for people with serious health problems, because the disease is most serious when one's immune system is weak.
Medications that are prescribed for acute Toxoplasmosis are:
Pyrimethamine — an antimalarial medication.
Sulfadiazine — an antibiotic used in combination with pyrimethamine to treat toxoplasmosis.
Clindamycin — an antibiotic. This is used most often for people with HIV/AIDS.
Spiramycin — another antibiotic. This is used most often for pregnant women to prevent the infection of their child.
(Other antibiotics such as minocycline have seen some use as a salvage therapy).
In people with latent toxoplasmosis, the cysts are immune to these treatments, as the antibiotics do not reach the bradyzoites in sufficient concentration.
Medications that are prescribed for latent Toxoplasmosis are:
Atovaquone — an antibiotic that has been used to kill Toxoplasma cysts in situ in AIDS patients.
Clindamycin — an antibiotic which, in combination with atovaquone, seemed to optimally kill cysts in mice.
However, in latent infections successful treatment is not guaranteed, and some subspecies exhibit resistance.
The parasite itself can cause various effects on the host body, some of which are not fully understood.
The evidence for behavioral effects on humans is relatively weak. There have been no randomized clinical trials studying the effects of toxoplasma on human behavior. Although some researchers have found potentially important associations with toxoplasma, it is possible that these associations merely reflect factors that predispose certain types of people to infection (e.g., people who exhibit risk-taking behaviors may be more likely to take the risk of eating undercooked meat).
Infants born to mothers who became infected with Toxoplasma for the first time during or just before pregnancy. Persons with severely weakened immune systems, such as those with AIDS. Illness may result from an acute Toxoplasma infection or reactivation of an infection that occurred earlier in
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