The hypotheses that schizophrenia may be linked to Toxoplasma gondii (T. gondii) — a parasite transmitted by soil, undercooked meat, and cat feces — is still viewed with skepticism. A new study, however, suggests that about one-fifth of cases may involve the parasite.
The research, published in the journal Preventive Veterinary Medicine, used epidemiological modeling methods to determine how many cases of schizophrenia may be attributable to T. gondii infection.
“Infection with Toxoplasma is very common, so, even if only a small percentage of people suffer adverse consequences, we could be talking about problems that affect thousands and thousands of people,” said Gary Smith, Ph.D., professor of population biology and epidemiology at the University of Pennsylvania’s School of Veterinary Medicine.
In the U.S., for example, just over one-fifth of the population is infected with T. gondii even though most aren’t aware of it. Certain populations need to be concerned, however, such as pregnant women and people with HIV or other diseases that weaken the immune system.
Previous supportive research has shown that the parasite is found in the brain as well as in muscles and that some antipsychotic drugs can actually stop the parasite from reproducing.
For the current study, the researchers wanted to determine the population attributabole fraction (PAF). This is a measurement used to determine how important a risk factor might be.
In this case, Smith explained that the PAF is “the proportion of schizophrenia diagnoses that would not occur in a population if T. gondii infections were not present.”
“In other words, we ask, if you could stop infections with this parasite, how many cases could you prevent?” Smith said. “Over a lifetime, we found that you could prevent one-fifth of all cases. That, to me, is significant.”
Smith noted that in some countries, the prevalence of T. gondii infection is much higher than in the U.S. and that these countries also have a higher incidence of schizophrenia.
“By finding out how important a factor T. gondii infection is, this work might inform our attitude to researching the subject,” Smith said.
“Instead of ridiculing the idea of a connection between T. gondii and schizophrenia because it seems so extraordinary, we can sit down and consider the evidence. Perhaps then we might be persuaded to look for more ways to reduce the number of people infected with Toxoplasma.”
Source: University of Pennsylvania