Cats - the danger that lurks within

I've got nothing against cats. Indeed, cats are some of my best friends. But there is an emerging strand of research linking a parasite that cats harbour to all kinds of mental disequilibrium. No, this is true. Let me run you through some of the highlights.

Toxoplasma gondii is a species of parasitic protozoa that has longed been known as the cause of toxoplasmosis. It can be carried by cats (and humans too), and can result in what is usually a minor and self-limiting disease that results in flu-like symptoms. However, it can also be lethal to unborn children, and this is why they say that pregnant women and those with compromised immune systems should avoid cats. Up to a third of people carry the parasite but our immune systems usually cope well enough with it so that very few people actually develop symptoms.

A new study in the Journal of Clinical Psychiatry seems to add to the evidence that the effects of the Toxoplasma gondii parasite might be far more wide-ranging than we ever imagined. In this admittedly cross-sectional study (which significantly reduces its explanatory appeal), blood serum evidence of having been infected with this parasite was positively related to a history of nonfatal suicidal self-directed violence. Does T.Gondii have a role to play in behaviour that seems to be self-destructive? Our research designs in this area are not yet powerful enough to answer this question, but it does seem worthy of more detailed investigation.

For many years, the theories concerning the influence of T. gondii on human behavior have been considered in the realm of conspiracy and UFO sightings. When the results of this line of research first started to come through, they were considered so bizarre that the data were thought to be flawed. However, this is starting to change as studies investigating its influence starts to move into the mainstream, including its possible influence in triggering episodes of schizophrenia and / or epilepsy. A number of independent studies seem to indicate that T.gondaii infection could be a factor in work and traffic accidents, as it can negatively influence attention and reaction times.

We don't yet know if most people just carry along with the parasite unaffected, or if it affects some people more than others. Some studies seem to indicate that infection can make rats less fearful, or can even changes human personalities e.g a pattern appeared in infected men: the longer they had been infected, the less conscientious they were.

What we know from this is that sometimes we don't know what we don't know. Ideas that can seem outlandish at one point in time can suddenly be mainstream and part of everyday life in a very short period. Evolution, perhaps? Or on a slightly more minor scale, the potential to use probiotics to treat mental illness?

It also tells us that it is sometimes worthwhile taking another look at what explains behaviour that we are struggling to understand. Sometimes the causes may come from places we may never have expected - but this isn't to let us completely of the hook. I don't want to hear any 'the cat made me do it' excuses.