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Houston Regional Group - News


by George Batten.

It's so small you can't see it. It's unlikely that you will know it if it affects you or a friend. You may know that toxoplasmosis seriously afffects unborn children and persons with weak immune systems (including people with AIDS and those being treated for cancer or organ transplants). You probably do not know about some other negative affects of Tosoplasma gondi (T.gondii) on society.

T. gondiiis a parasitic protozoan that infects "warm blooded" animals, including about one third of humans in developed countries, causing the disease Toxoplasmosis (sometimes shortened to "toxo"). It has an interesting trait: mice and rats that it infects tend to lose their fear of cats! Moreover, it reproduces sexually only in the intestines of felids (cats, large and small; tests show this for at least 17 felid species). The sexual reproduction produces oocysts ("eggs") which are shed in the cat's feces. Oocysts can survive for a long time (up to two years) in the soil. Infection of tissues, including the brain, is from asexual reproduction, which occurs in all infected animals, and produces tissue cysts, but does not produce shedding of infectious material. Once established, the infection is for the lifetime of the animal or human.

Infection occurs by:

  • consumption of raw or undercooked meat containing T. gondii tissue cysts,
  • ingestion of water, soil, vegetables; or anything contaminated with oocysts shed in the feces of an infected cat; or;
  • transmission from mother to fetus, particularly when T. gondii is contracted during pregnancy.

Correspondingly, risk factors for T. gondii infection have been found to be:

  • exposure to or consumption of raw or undercooked meat,
  • drinking unpasteurized goat milk,
  • contact with soil,
  • eating unwashed raw vegetables or fruits, and
  • cleaning cat litter boxes.

Pregnant women are advised to avoid cleaning cat litter boxes. Some fish off the U. S. Pacific coast have been infected with T. gondii, presumably because of runoff from cat litter disposal (so, enjoy sushi if you want to, but keep the risk in mind - by the way, T. gondii in runoff from cat litter has been implicated in the death of California sea otters). Numerous studies have found that living in a household with an indoor cat is not a significant risk factor for T. gondii infection.

What is the effect of T. gondii infection on humans? Accumulating evidence suggests that latent infection may influence a range of behaviors and tendencies. It has been associated with impaired psychomotor performance, enhanced risk-taking personality profiles, and higher incidence of automobile accidents. There are correlations with OCD, Parkinson's disease, Alzheimer's disease, suicide in patients with mood disorders, and bipolar disorder, but not with major depression or chronic depression lasting at least two years (dysthymia). There are numerous studies linking the infection to schizophrenia.

Most of the studies have been retrospective: T.gondi seropositivity was measured after the onset of the disease or behaviorial trait, so the results are suggestive, but cause and effect has not been demonstrated. Some serological tests made before the onset of schizophrenia have been positive, however. The same is true of the large cohort study mentioned below (reference 2).

As you can see, there is accumulating evidence that T. gondii has a negative effect on human society. Just the treatment of correlated mental disorders is costly, but who can say that some antisocial activity is not caused by T. gondii? Certainly, not everyone infected will have antisocial tendencies, but one can wonder about some extreme cases. I would like to know if there is a correlation between T. gondii seropositivity and road rage; the same for corporate and political decisions that affect millions of people; the same for mass shootings (fortunately, the sample size for the latter is so small that it may not be possible to draw any conclusions). Are infected people more inclined to support large colonies of feral cats?

What can be done to limit this disease? The first step, obviously, is education: people need to know the risk factors and how to avoid them. Then, the reservoir of T. Gondii needs to be reduced as much as possible. This means that we must reduce the population of outdoor cats as much as possible. In particular, we must stop supporting feral cat colonies (colonies which BARC - Bureau of Animal Regulation and Care - Houston's animal control organization, advocates). The approximately 10% of households that feed stray cats should stop doing that.

Much of the information reported here appears on the Wikipedia web site Toxoplasma gondii , some parts of which have been copied verbatim. A summary of the effects of T. gondi is in reference 1 below, the abstract for which is available on line at the PubMed web site. Reference 2, below, is a complete scientific paper on a large-cohort study of the effects of T. gondii on traffic accidents, avaialble online here.

For emphasis:

  • Keep your cats indoors.
  • Do not feed stray cats.
  • Wear good gloves when gardening where cats defecate (most places where cats have lived; sanitize the gloves and wash your hands afterward).

Some references:

  1. J. Flegr, "Influence of latent Toxoplasma infection on human...," Journel of Experimental Biology, 2013 Jan 1; 216(Pt 1):127-33.
  2. J. Flegr, et al, "Increased incidence of traffic accidents...," BMC Infectious Diseases, 2009, v. 9:72

Acknowledgement: The author greatly appreciates the aid of Page Williams, who mad many useful comments, and suggestions, and provided reference material.

Last updated:  04/01/2013.   Content 2013-2013 by the Sierra Club.