I've been reading the Stanley Medical Institute research on schizophrenia and toxoplasmosis. This is a well-written news article about the behavior of rats infected by toxoplasma. You may never have heard of "toxo" but recent findings show that it is not a mostly benign parasite as was believed. And about a quarter of all human beings are infected! There are indications that toxo could be the cause (or at least a cause) of schizophrenia. Combine this with the fact that toxo reproduces inside our beloved housecats, and that a significant percentage of schizophrenics were exposed to cats in childhood, and it gets pretty scary. Exposure to cats is not even necessary: toxo oocytes (eggs) are everywhere, in the dirt, the air, even in meat, since the protozoa can infect any mammal (but freezing and cooking kills them).
Toxo oocytes are most abundant in places where cats defecate - like your neighborhood sandbox.
Toxoplasma affects behavior. In rats, toxoplasmosis causes its hosts to crave the odor of cat urine, causing the rat's virtual suicide by becoming dinner for the feline, where the toxo can finally complete its life cycle. The parasite acts by forming cysts in the brain, in particular the amygdala, center of fear-related behavior. Is this the reason for the paranoia component of schizophrenia? Toxo also has the genes encoding two critical enzymes needed to make dopamine, which individuals with schizophrenia are thought to have in excess (Wikipedia has an article titled "Dopamine hypothesis of schizophrenia"). Toxoplasmosis is correlated with higher suicide rates, increased activity, loss of concentration, slower reaction time. All of these traits help the cats catch infected rats, but what happens to the poor humans who get this infection? "The effects of T. Gondi on rodents' brains are highly specific", says the research paper. So, schizophrenia would be the effect of very specific chemical activity, meant for manipulation of rodent behavior, on the human brain.
Some excerpts from the Stanley paper:
From the abstract:
"Toxoplasma gondii [is] a protozoan parasite that causes toxoplasmosis and is carried by cats and other felines. Until recently, toxoplasmosis was thought to be a problem only for pregnant women who, if they became infected with T. gondii during their pregnancy, risked having the organism cause damage to the growing fetus. This is why pregnant women are advised to not change the litter in the cat litter box. Infection with T. gondii in other adults and children was thought to be either asymptomatic or to cause an influenza-like or mononucleosis-like syndrome. It now seems possible that T. gondii may be associated with schizophrenia and perhaps other psychiatric syndromes."
"Assuming that cats defecated in a completely random manner, the researchers calculated that each square foot of ground would be burdened with between 9 and 434 infected T. gondii oocysts each year. [...] Cats, of course, do not defecate randomly but favor specific outdoor spots, meaning that such spots are inevitably burdened with a very large number of oocysts."
"Children’s play areas and sandboxes are common places for cats to defecate because they can use the area’s loose soil or sand to bury their feces. [...]each sandbox would contain approximately 85 million viable oocysts at any given time."
"As the cat feces dry, the oocysts may become aerosolized. They can thus be inhaled by a person changing cat litter or just walking in an area where cats have defecated."
" Unwashed vegetables from gardens can also carry oocysts. Studies have also shown that cockroaches and flies can carry oocysts from cat feces to fruits and vegetables."
"In countries like France, which has a high rate of T. gondii-infected individuals, the most important source of transmission is thought to be undercooked meat. [...] The seroprevalence of toxoplasmosis has decreased sharply in the United States and Europe in the past forty years It has been speculated that this is because of the increased use of frozen meat, since freezing kills the tissue cysts."
"Humans may become infected with T. gondii at any time in life. In immunocompetent individuals, the infection is asymptomatic 90 percent of the time. In the other 10 percent, the "primary infections cause a mild, mononucleosis-like illness with low-grade fever, malaise, headache, and cervical lymphadenopathy."
"It is clearly established that congenital infections with T. gondii, especially early in pregnancy, can produce intracranial calcifications, mental retardation, deafness, seizures, and retinal damage."
" there is evidence that the effects of T. gondii on the brain are highly specific. For example, in experiments in which mice have been infected, the mice may have profound and widespread brain pathology and deficits in motor coordination and sensory deficits, but their cognitive skills remain relatively intact "
"In areas where felines are rare, the prevalence rates of both toxoplasmosis and schizophrenia appear to be low. "
"Antipsychotic medications have been shown to have antiprotozoal activity."