Blog — May 29, 2011

An article by Christof Koch in the latest Scientific American. com suggests that the parasitic protozoa Toxoplasma gondii, which is carried in the guts of cats,  could have human health implications that go beyond its well-known deleterious impacts on human fetuses. It is possible that the parasite can actually “take over” the brain of the host and make it behave in ways that are detrimental to the host. Studies of rats and mice have shown that individuals infected with T. gondii lose their fear of cats and cat urine, thus making them more susceptible to predation by cats. The behavioral manipulation is quite specific; infected mice and rodents don’t appear to be sick, nor do they lose weight. They simply lose their strong and innate fear of cats, thus giving the T. gondii a better change of ending up in the gut of a cat–a necessary part of its life cycle. Interestingly, human schizophrenic patients are three times more likely to carry antibodies to T. gondii than are controls that are not schizophrenic. The exact link between toxo and psychotic diseases in humans is, according to the author, “tantalizing, but remains murky.” However, a prospective study tracking the road safety of Czech recruits during their 18-month compulsory military service, found a rate of accidents six times higher in drivers infected with toxo than in those that were not infected. Are such men engaging in riskier behavior as a result of their exposure to toxo, or were their reactions simply slower? Although the linkages are unclear, toxo has also been recently implicated in human Parkinson’s disease and autism. One thing is clear; these relationships are now being studied intensively, and if the connections pan out, then I suspect that CDC and public health experts will become increasingly supportive of the control of feral and free-roaming housecats. Cats also spread many other dangerous zoonotic diseases such as rabies, which should also be cause for serious concern.   Human health concerns, combined with the catastrophic impact of feral and free-roaming cats on our native wildlife, including endangered species, should be enough to cause authorities to move quickly to control feral cat populations and ban ineffective TNR management, but this has not been the case. Perhaps human health concerns will do the trick.

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Michael Hutchins