Recent epidemiologic studies indicate that infectious agents may contribute
to some cases of schizophrenia. In animals, infections with Toxoplasma
gondii can alter behavior and neurotransmitter function. In humans, acute
infection with the cat virus "T. gondii" can produce psychotic
symptoms similar to those displayed by persons with schizophrenia. Two
other studies found that exposure to cats in childhood was a risk factor
for the development of schizophrenia.
Since 1953, a total of 19 studies of T. gondii antibodies in persons with schizophrenia and other severe psychiatric disorders and in controls have been reported; 18 reported a higher percentage of antibodies in the affected persons; in 11 studies the difference was statistically significant.
Whether any geographic association exists between the prevalence of toxoplasmosis and the prevalence of schizophrenia is unknown. France, which has a high prevalence of Toxoplasma-infected persons, was reported to have first-admission rates for schizophrenia approximately 50% higher than those in England (41). Ireland also has a high rate of Toxoplasma-infected persons in rural areas (42)
Dr. Robert H. Yolken, the director of the Stanley Laboratory at Johns Hopkins University, and his colleagues reviewed military medical records. They found that soldiers who developed schizophrenia were twice as likely as other soldiers to show signs of Toxoplasma infection in blood samples.
Action: Minimize exposure of young children to cats, and or observe
the following prevention tips below (source: http://www.fabcats.org/toxo.html): Minimize exposure of children to un-cooked or rare meat (which can also be a means of transmission of the virus). Dr. Torrey (the leading researcher on this topic) advises parents not to buy pet cats for young children, and to cover
their sandboxes to prevent cats from using them as litter boxes.
How can the risk of transmission of toxoplasma from a cat to
its owner be reduced?
Although the risk of transmission of infection from a cat to its owner
is very low, this can be reduced further and/or its consequences minimised
by adopting the following recommendations:
- People in 'high risk' groups should not have contact with the cat's
litter tray. Where possible, only non-pregnant and immunocompetent people
(i.e. not those people with diseases or drug therapy suppressing their
immune system) should handle cat litter trays (following all of the
- Empty litter trays daily so that oocysts do not have sufficient time
to sporulate (become infective) whilst in the litter tray.
- Wear gloves when handling cat litter and wash hands thoroughly after
cleaning the litter tray.
- Use litter tray liners if possible and periodically clean the litter
tray with detergent and scalding water (which kills oocysts) eg fill
the litter tray with boiling water and leave for 5 - 10 minutes before
- Dispose of cat litter safely. For example, seal it in a plastic bag
before putting it with other household waste.
- Cover children's sandpits when not in use to prevent cats using them
as litter trays.
- Feed only properly cooked food or commercial cat food to your cat
to avoid infection.
- Washing hands after contact with a cat (especially before eating)
is a sensible hygiene precaution.
- If very concerned, ask your vet to check your cat's Toxoplasma titre
(antibody test for exposure to T gondii):
a. Cats with a positive titre have been infected in the past and will
not be a source of infection in the future as they have completed their
period of oocyst shedding.
b. Cats with a negative titre have not been infected with T gondii
in the past and are likely to shed oocysts in their faeces for a short
time if they become infected in the future. The risk of acquiring infection
can be minimised by:
- Avoiding feeding raw meat to the cat to reduce the risk of T
gondii infection (see point 7 above).
- Keeping the cat indoors to prevent hunting and access to intermediate
hosts such as voles and mice
How can the risk of transmission of toxoplasma from other sources
These measures are essential in all 'high risk' groups of people (see
above) and are also sensible routine hygiene precautions:
- Gloves should be worn when gardening and hands thoroughly washed after
contact with soil which may contain sporulated (infectious) oocysts.
- Gloves should be worn when handling food to prevent exposure to oocysts
and tissue cysts. Hands should always be washed thoroughly afterwards.
- Fruit and vegetables should be thoroughly washed before eating to
remove any oocysts present on their surface.
- All food preparation surfaces and utensils should be cleaned with
detergent in warm water before and after use to inactivate any tissue
- Meat should be cooked to a minimum of 58oC for 10 minutes or 61oC
for 4 minutes to kill the tissue cysts (Dubey et al 1990). Microwaving
is not a safe way to kill tissue cysts as the heating is uneven. T
gondii oocysts can remain infectious when stored in a refrigerator
(4oC) for up to 54 months (Dubey 1998).
- Freezing meat at -12oC to -20oC for three days kills tissue cysts
as does curing or smoking (Dubey 1988, Lunden and Uggla 1992).
- Gamma irradiated food is free from any risk of infection.
- If drinking a non-mains water supply, boil or filter before drinking
to remove oocysts.
Supporting Research (a sample):