is a
Parasitic Disease caused by the
Parasite ''
Toxoplasma Gondii ''. It infects most animals and causes
Human Parasitic Disease s, but the primary host is the felid (cat) family. Cats get infected by eating infected
Rat s. Rats get infected by accidentally absorbing
Cat Faeces . The parasite subtly alters the rat's behavior. Whereas healthy rats avoid areas that smell like cat urine, infected rats may actually seek these areas out.
People usually get infected by eating raw or undercooked
Meat , or more rarely, by contact with cat faeces.
At least one third of the world population may have contracted a toxoplasmosis infection in their lifetime but, after the acute infection has passed, the parasite rarely causes any symptoms in otherwise healthy adults. However, people with a weakened
Immune System are particularly susceptible, such as people infected with
HIV . The parasite can cause
Encephalitis (inflammation of the brain) and
Neurologic Disease s and can affect the
Heart ,
Liver , and
Eye s (
Chorioretinitis ).
Transmission may occur through:
- Ingestion of raw or partly cooked meat, especially pork, lamb, or venison, or by hand to mouth contact after handling undercooked meat. Infection prevalence is higher in countries that traditionally eat undercooked meat, such as France . This seems to be by far the most common route of infection.
- Ingestion, accidental or otherwise, of contaminated cat faeces. This can occur through hand to mouth contact following gardening, cleaning a cat's Litter Box , children's sandpits, or touching anything that has come into contact with cat faeces.
- Contamination of knives, utensils, cutting boards and other foods that have had contact with raw meat.
- Drinking water contaminated with Toxoplasma.
- Ingestion of raw or unpasteurized milk and milk products, particularly those containing goat's milk.
- The reception of 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 cooling down to subzero temperatures and chemical disinfectants such as bleach and can survive in the environment for over a year. It is, however, susceptible to high temperatures, and is killed by cooking. Cats excrete the pathogen for a number of weeks or months 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.
Although the pathogen has been detected on the fur of cats, the pathogen has not been found in a 'ripe' form, and direct infection from handling cats is generally believed to be very rare.
Congenital toxoplasmosis is a special form in which an unborn child is infected via the
Placenta . This is the reason that pregnant women should be checked to see if they have a
Titer to toxoplasmosis. A titer indicates previous exposure and largely ensures the unborn baby's safety. If a woman receives her first exposure to Toxoplasma while pregnant then the baby is at particular risk. A woman with no previous exposure should avoid handling raw meat, exposure to cat faeces, and gardening (a common place to find cat feces). Most cats are not actively shedding
Oocyst s 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/or by having someone else empty the litterbox.
Treatment is very important for recently infected
Pregnant women, to prevent infection of the
Foetus . 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 very young.
Infection has two stages:
During '''s, 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 persons 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 newborns have serious eye or brain damage at birth.
A combination of
Sulfadiazine and
Pyrimethamine should be given.
Most patients who become infected with ''
Toxoplasma Gondii '' and develop toxoplasmosis do not know it. In most non-immunodeficient patients, the infection enters a phase, during which only
Bradyzoite s are present, forming
Cyst s 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.
The cysts are immune to the standard acute treatments.
The antibiotic seemed to optimally kill cysts
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- 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 persons with AIDS. This results from an acute Toxoplasma infection or an infection that occurred earlier in life that reactivates and causes damage to the brain, eyes, or other organs.
The findings of behavioral alteration in rats and mice have lead some scientists to speculate that toxoplasma may have similar effects in humans, even in the latent phase that had previously been considered
Asymptomatic . Toxoplasma is one of a number of parasites which require alteration of host's behaviour for their life cycle. The changes observed are likely due to the presence of cysts in the
Brain , which produce or induce production of a neurotransmitter, possibly dopamine, therefore acting similarly to
Dopamine Reuptake Inhibitor type
Antidepressants .
The evidence for behavioral effects on humans, although intriguing, 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.
Studies have found that toxoplasmosis is associated with an increased auto accident rate, roughly doubling or tripling the chance of an accident relative to uninfected people . This may be due to the decreased reaction times that are associated with infection . "If our data are true then about a million people a year die just because they are infected with toxoplasma," the researcher Jaroslav Flegr told ''The Guardian''. The data shows that the risk decreases with time after infection, but is not due to age . Ruth Gilbert, medical coordinator of the European Multicentre Study on Congenital Toxoplasmosis, told ''BBC News Online'' these findings could be due to chance, or due to social and cultural factors associated with toxoplasma infection.
Other studies suggest that the parasite may influence personality. There are claims of toxoplasma causing antisocial attitudes in men and promiscuity (or even "signs of higher intelligence") in women, and greater susceptibility to
Schizophrenia and
Manic Depression in all infected persons. A 2004 study found that toxoplasma "probably induce
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The possibility that toxoplasmosis is one cause of schizophrenia has been studied by scientists at least since 1953. These studies, many written in languages other than English, had attracted little attention from U.S. researchers until they were publicized through the work of prominent psychiatrist and advocate
E. Fuller Torrey . In 2003, Torrey published a review of this literature, reporting that almost all the studies had found that schizophrenics suffer from elevated rates of toxoplasmosis infection. These types of studies are suggestive but cannot confirm a causal relationship (because of the possibility that schizophrenia increases the likelihood of toxoplasmosis infection, rather than the other way around). .
In the U.S. NHANES III national probability sample, 22.5% of 17,658 persons >12 years of age had Toxoplasma-specific
IgG Antibodies , indicating that they had been infected with the organism. It is thought that between 30% and 60% of the world's population are infected. However, there is large variation countries: in France, for example, about 85% of the population are carriers, probably due to a high consumption of raw and lightly cooked meat.
A University of California Davis study of dead
Sea Otter s collected from 1998 to 2004 found that toxoplasmosis was the cause of death for 13% of the animals. Proximity to freshwater outflows into the ocean were a major risk factor. Ingestion of oocysts from cat faeces is considered to be the most likely ultimate source.
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