Tuesday, June 12, 2012

Increased Risk of T. gondii in Free Range Animals

There has been some recent press surrounding Toxoplasmosis gondii, a parasite that has been identified as one of the leading causes of foodborne related deaths and hospitalizations. This parasite is acquired when individuals consume undercooked meat that is infected with the cysts imbedded in the tissue or when people come in contact with contaminated cat feces (cats are a natural host organism and they excrete/poop the more resistant oocyte). It can be a major health issue in immunosuppressed individuals including pregnant women with the infection being passed on congenitally, and it can cause mild illness in healthy individuals. (CDC link below) It can cause acute ocular disease. (Other studies have linked T. gondii infection with schizophrenia - citation below). 

The concern proposed in this journal article is that organically raised meat is more likely to be a source of T. gondii. Free range pigs (organically raised) are more likely to be contaminated with the organism in that their diet is less controlled and so they are more likely to eat in places contaminated by cat feces. In one study, 17 of 33 organically raised pigs from Michigan were contaminated with T. gondii (in another study, the level in commercial pork was much lower ~0.3%). In free range chickens, the prevalence was higher (est greater than 17%) compared to commercially raised poultry (0%). The organism or the antibodies to the organism have also been found in sheep, goats (and unpasteurized goat milk), and venison.

Adequate cooking and freezing are important to prevent infection, especially free range/organically raised pork (as well as goat and sheep). Of course, preventing contaminated by infected cats is important. (Outdoor cats are more likely to become contaminated than indoor cats.)

(Free range animals may also be a higher risk for other pathogenic paracites such as Trichinella).

Foodborne Toxoplasmosis
Jeffrey L. Jonesa and J.P. Dubeyb
Clinical Infectious Disease. (2012)
Toxoplasmosis can be due to congenital infection or acquired infection after birth and is one of the leading illnesses associated with foodborne hospitalizations and deaths. Undercooked meat, especially pork, lamb, and wild game meat, and soil contaminated with cat feces on raw fruits and vegetables are the major sources of foodborne transmission for humans. The new trend in the production of free-range organically raised meat could increase the risk of Toxoplasma gondii contamination of meat. Foodborne transmission can be prevented by production practices that reduce T. gondii in meat, adequate cooking of meat, washing of raw fruits and vegetables, prevention of cross contamination in the kitchen, and measures that decrease spread of viable oocysts into the environment.

Maternal Exposure to Toxoplasmosis and Risk of Schizophrenia in Adult OffspringAlan S. Brown, M.D.; Catherine A. Schaefer, Ph.D.; Charles P. Quesenberry, Ph.D.; Liyan Liu, M.D., M.Sc.; Vicki P. Babulas, M.P.H.; Ezra S. Susser, M.D., Dr.P.H.
Am J Psychiatry 2005;162:767-773. 10.1176/appi.ajp.162.4.767
OBJECTIVE: The authors examined the relationship between maternal antibody to toxoplasmosis and the risk of schizophrenia and other schizophrenia spectrum disorders in offspring. Toxoplasmosis is known to adversely affect fetal brain development. METHOD: In a nested case-control design of a large birth cohort born between 1959 and 1967, the authors conducted serological assays for Toxoplasma antibody on maternal serum specimens from pregnancies giving rise to 63 cases of schizophrenia and other schizophrenia spectrum disorders and 123 matched comparison subjects. Toxoplasma immunoglobulin (Ig)G antibody was quantified by using the Sabin-Feldman dye test. The Ig titers were classified into three groups: negative (<1:16) (reference), moderate (1:16–1:64), and high (≥1:128). RESULTS: The adjusted odds ratio of schizophrenia/schizophrenia spectrum disorders for subjects with high maternal Toxoplasma IgG antibody titers was 2.61 (95% confidence interval=1.00–6.82). There was no association between moderate Toxoplasma Ig antibody titers and the risk of schizophrenia/spectrum disorders. CONCLUSIONS: These findings suggest that maternal exposure to toxoplasmosis may be a risk factor for schizophrenia. The findings may be explained by reactivated infection or an effect of the antibody on the developing fetus. Given that toxoplasmosis is a preventable infection, the findings, if replicated, may have implications for reducing the incidence of schizophrenia. 

Taxoplasmosis from the CDC website  http://www.cdc.gov/parasites/toxoplasmosis/gen_info/index.html

Epidemiology & Risk Factors

Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. In the United States it is estimated that 22.5% of the population 12 years and older have been infected with Toxoplasma. In various places throughout the world, it has been shown that up to 95% of some populations have been infected with Toxoplasma. Infection is often highest in areas of the world that have hot, humid climates and lower altitudes.
Toxoplasmosis is not passed from person-to-person, except in instances of mother-to-child (congenital) transmission and blood transfusion or organ transplantation. People typically become infected by three principal routes of transmission.
Foodborne transmission
The tissue form of the parasite (a microscopic cyst consisting of bradyzoites) can be transmitted to humans by food. People become infected by:
· Eating undercooked, contaminated meat (especially pork, lamb, and venison)
· Accidental ingestion of undercooked, contaminated meat after handling it and not washing hands thoroughly (Toxoplasma cannot be absorbed through intact skin)
· Eating food that was contaminated by knives, utensils, cutting boards, or other foods that had contact with raw, contaminated meat
Animal-to-human (zoonotic) transmission
Cats play an important role in the spread of toxoplasmosis. They become infected by eating infected rodents, birds, or other small animals. The parasite is then passed in the cat's feces in an oocyst form, which is microscopic.
Kittens and cats can shed millions of oocysts in their feces for as long as 3 weeks after infection. Mature cats are less likely to shed Toxoplasma if they have been previously infected. A Toxoplasma-infected cat that is shedding the parasite in its feces contaminates the litter box. If the cat is allowed outside, it can contaminate the soil or water in the environment as well.
People can accidentally swallow the oocyst form of the parasite. People can be infected by:
· Accidental ingestion of oocysts after cleaning a cat's litter box when the cat has shed Toxoplasma in its feces
· Accidental ingestion of oocysts after touching or ingesting anything that has come into contact with a cat's feces that contain Toxoplasma
· Accidental ingestion of oocysts in contaminated soil (e.g., not washing hands after gardening or eating unwashed fruits or vegetables from a garden)
· Drinking water contaminated with the Toxoplasma parasite 

Mother-to-child (congenital) transmission
A woman who is newly infected with Toxoplasma during pregnancy can pass the infection to her unborn child (congenital infection). The woman may not have symptoms, but there can be severe consequences for the unborn child, such as diseases of the nervous system and eyes

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