• Supporting Scientific Evidence
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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:

1. 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 guidelines below).
2. Empty litter trays daily so that oocysts do not have sufficient time to sporulate (become infective) whilst in the litter tray.
3. Wear gloves when handling cat litter and wash hands thoroughly after cleaning the litter tray.
4. 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 emptying.
5. Dispose of cat litter safely. For example, seal it in a plastic bag before putting it with other household waste.
6. Cover children's sandpits when not in use to prevent cats using them as litter trays.
7. Feed only properly cooked food or commercial cat food to your cat to avoid infection.
8. Washing hands after contact with a cat (especially before eating) is a sensible hygiene precaution.
9. 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 be reduced?

These measures are essential in all 'high risk' groups of people (see above) and are also sensible routine hygiene precautions:

1. Gloves should be worn when gardening and hands thoroughly washed after contact with soil which may contain sporulated (infectious) oocysts.
2. Gloves should be worn when handling food to prevent exposure to oocysts and tissue cysts. Hands should always be washed thoroughly afterwards.
3. Fruit and vegetables should be thoroughly washed before eating to remove any oocysts present on their surface.
4. All food preparation surfaces and utensils should be cleaned with detergent in warm water before and after use to inactivate any tissue cysts.
5. 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).
6. Freezing meat at -12oC to -20oC for three days kills tissue cysts as does curing or smoking (Dubey 1988, Lunden and Uggla 1992).
7. Gamma irradiated food is free from any risk of infection.
8. If drinking a non-mains water supply, boil or filter before drinking to remove oocysts.

Supporting Research (a sample):

• Interview with schizophrenia researcher Dr. E. Fuller Torrey on the issue of cats and schizophrenia
• Toxoplasma gondii and Schizophrenia - Summary of the Data
• Toxoplasma gondii and Schizophrenia (Research)
  
• Herpesviruses and Toxoplasma gondii in orbital frontal cortex of psychiatric patients (Research)
• The antecedents of psychoses: a case-control study of selected risk factors (Research)
• Could schizophrenia be a viral zoonosis transmitted from house cats? (Research)
• Evaluation of Torrey and Yolken's feline viral zoonosis theory of schizophrenia (Research)