Chickens
Due to a lack of exposure to the outdoors, chickens raised in large-scale indoor confinement operations are not commonly infected with T. gondii. Free-ranging or backyard-raised chickens are much more commonly infected. A survey of free-ranging chickens in the United States found its prevalence to be 17–100%, depending on the farm. Because chicken meat is generally cooked thoroughly before consumption, poultry is not generally considered to be a significant risk factor for human T. gondii infection. Cattle
Although cattle and buffalo can be infected with T. gondii, the parasite is generally eliminated or reduced to undetectable levels within a few weeks following exposure. Tissue cysts are rarely present in buffalo meat or beef, and meat from these animals is considered to be low-risk for harboring viable parasites. Horses
Horses are considered resistant to chronic T. gondii infection. However, viable cells have been isolated from US horses slaughtered for export, and severe human toxoplasmosis in France has been epidemiologically linked to the consumption of horse meat. Domestic cats
In 1942, the first case of feline toxoplasmosis was diagnosed and reported in a domestic cat in Middletown, New York. The investigators isolated oocysts from feline feces and found that the oocysts could be infectious for up to 12 months in the environment.The seroprevalence of T. gondii in domestic cats, worldwide has been estimated to be around 30–40% and exhibits significant geographical variation. In the United States, no official national estimate has been made, but local surveys have shown levels varying between 16% and 80%.
While the majority of these studies tested people already diagnosed with schizophrenia for T. gondii antibodies, associations between T. gondii and schizophrenia have been found prior to the onset of schizophrenia symptoms. Sex differences in the age of schizophrenia onset may be explained in part by a second peak of T. gondii infection incidence during ages 25–30 in females only. Although a mechanism supporting the association between schizophrenia and T. gondii infection is unclear, studies have investigated a molecular basis of this correlation. Antipsychotic drugs used in schizophrenia appear to inhibit the replication of T. gondii tachyzoites in cell culture. Supposing a causal link exists between T. gondii and schizophrenia, studies have yet to determine why only some individuals with latent toxoplasmosis develop schizophrenia; some plausible explanations include differing genetic susceptibility, parasite strain differences, and differences in the route of the acquired T. gondii infection.Correlations have also been found between antibody titers to T. gondii and OCD, as well as suicide among people with mood disorders including bipolar disorder. Positive antibody titers to T. gondii appear to be uncorrelated with major depression or dysthymia. Although there is a correlation between T. gondii and many psychological disorders, the underlying mechanism is unclear. A 2016 study of 236 persons with high levels of toxoplasmosis antibodies found that "there was little evidence that T. gondii was related to increased risk of psychiatric disorder, poor impulse control, personality aberrations or neurocognitive impairment".