Headline writers have had a lot of fun over the past few years writing about toxoplasmosis and potential associations with neurological and behavioural disorders in people. Cats are the main natural host of Toxoplasma gondii, so “crazy cat lady” and other predictable headlines have ensued.
But, what is the real risk?
The answer is still unclear, and that’s important to remember. Some studies have implicated exposure to this parasite as a risk factor for conditions such as schizophrenia. These studies have been of varying strengths, with some being pretty weak (which news articles often fail to mention). It’s an enigmatic parasite and good information is hard to get for a variety of reasons. One reason is that exposure to it is pretty common. A large percentage of people have been exposed to this parasite in their lives, and discerning why they tested positive (or how they were exposed) and whether that relates to any subsequent disease can be difficult. Also, factors that increase the risk of exposure might themselves be risk factors for diseases (i.e. the same thing that increases the risk of illness also increases the risk of exposure to Toxoplasma, but it may not be the Toxoplasma that is causing the illness). There are lots of different sources of exposure to this parasite too. While cats are the natural hosts and can pass Toxoplasma oocysts (eggs) in their feces, contact with cats is actually an uncommon source of exposure. People can be exposed from food, water and the environment, complicating things further.
All this leads into a recent study in PLOS One (Sugden et al 2016) entitled “Is Toxoplasma gondii infection related to brain and behavior impairments in humans? Evidence from a population-representative birth cohort”.
Not the most exciting title, but it is an interesting study nonetheless. The study investigated the relationship between the presence of antibodies against Toxoplasma (an indication of previous exposure/infection) and neuropsychiatric disorders (schizophrenia, major depression), poor impulse control (suicidal behaviour and criminal activity), personality and neurocognitive performance.
Overall, there was nothing remarkable. There was a marginally higher (but not statistically significant) rate of suicide attempt in the infected group. Since it wasn’t statistically significant and quite a few things were evaluated (the more tests you do the greater the chance for a random error) the authors concluded “there was little evidence that T. gondii was related to increased risk of psychiatric disorder, poor impulse control, personality aberrations or neurocognitive impairment.”
Regardless of the outcome of this study, the risk to cat owners is actually very low, and it can be made even lower by using some very basic management and hygiene practices (all revolving around the concept of “don’t eat poop”). These, and other relevant information about toxoplasmosis, can be found in our Toxoplasmosis fact sheet on the Worms & Gemrs Resources – Pets page.