Toxoplasmosis: More than meets the eye?

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You may have heard of Toxoplasmosis, especially if you are a cat owner and you become pregnant. Advice still exists to avoid cats during pregnancy but with adequate precautions, you can easily maintain relationships with your feline friend. Here integrative therapist Marta Browne keep Pet Problems Solved up to date with the latest research on this parasite…

Toxoplasmosis: More than meets the eye?

What is Toxoplasmosis?

Open any standard textbook on parasitology and you’ll note the classic Toxoplasma gondii, a relative of the malaria-causing Plasmodium falciparum, is almost always reported as a fairly prevalent protozoan parasite (infecting up to 50% of the global population by some accounts!) that rarely causes significant symptoms in humans as the cysts formed in the brain are kept dormant by effective immune systems.

These texts will detail transmission that is primarily through contact with cat faeces, consumption of raw contaminated meat or poor hygiene practices, and that only pregnant women or immunocompromised individuals should take extra precautions beyond basic hygiene practices. In fact, as little as a decade ago, standard university teaching was still outlining that T. gondii infection was only really a problem in humans who seroconverted during their pregnancy or developed AIDS, cancer or otherwise became immunocompromised, which lowered the immune system safeguards that kept the cysts dormant and then allowed the parasite to become active within tissues.

Toxoplasmosis symptoms

Other than the ‘flu-like’ symptoms that resolve within weeks or months post initial infection, including fever, muscle aches and tender lymph nodes, there remain risks for further physiological damage with each relapse, such as retinochoroiditis leading to progressive loss of vision or congenital disease (including vision loss, mental disability, cerebral calcification, seizures or other nervous system damage in the infant) from a previously infected woman who suffers a reactivation of the infection during a subsequent pregnancy.

More in-depth research, however, has implicated T. gondii as potentially a far more insidious parasite than previously suspected (1), although the full picture in terms of human behaviour is not yet clear with some studies indicating the effect in humans may be quite weak, despite promising patterns in rodents.

The findings of altered behaviours in rodents has led to speculation that even the latent phase may not be as asymptomatic and innocuous as previously thought with the suggestion that psychosis-spectrum conditions are related to infection through changes to dopamine signalling and reduced expression of genes within the dopamine pathway. (3)

A study has suggested that seropositivity for T. gondii does not result in increased susceptibility to neuropsychiatric disorders, poor impulse control, impaired neurocognitive ability, or aberrant personality functions. (4) However, the study did note lowered scores on a verbal learning and memory test, and that attempted suicide was more common in seropositive individuals, a trend consistent with previous studies. Interestingly, this study did not find a link to schizophrenia, a finding that has been shown in about 40 published studies on the matter, although the authors did note a possible false negative due to small size.

While some studies certainly indicated seropositive individuals assessed showed an increased susceptibility to schizophrenia and depression (Torrey, 2003), overall the body of research focused on the schizophrenia connection confirms correlation, but does not necessarily confirm causation. It may be that these associations simply signify factors that predispose certain types of people to infection.

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Toxoplasmosis Prevention

Precautions against T. gondii in developed countries are simple and generally encompass adequate hygiene and safe food handling techniques. These include:

handwashing and protection – gloves when handling raw meat, gardening or cleaning litter boxes, and washing hands before meals
thorough cooking of meat (avoid rare or medium-rare)
washing of plant foods to remove all traces of soil
washing of cutting boards, knives and other implements used in preparing raw meats
cleaning litter trays and delegating this duty if immunocompromised
keeping companion cats indoors as much as possible and preventing them from eating raw meat
discouraging strays from entering the property
covering or blocking off sandy areas, such as children’s sandpits or open garden beds

In developing countries, access to clean water, safe meat and sanitation mean that even these basic precautions can be difficult to accomplish, leading to incidence of up to 95% in some communities. Interestingly, some developed nations also have surprisingly high infection rates – such as Germany, where about 65% of the population are carriers, most likely related to a high consumption of raw or lightly cooked meat. (2)

Article References
1. Flegr, J. (2013). Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma–human model in studying the manipulation hypothesis. Journal of Experimental Biology, 216: 127-133.

Flegr, J. P. (2014). Toxoplasmosis – A Global Threat. Correlation of Latent Toxoplasmosis with Specific Disease Burden in a Set of 88 Countries. PLoS One, 9(3).
Prandovszky E., G. E. (2011). The neurotropic parasite Toxoplasma gondii increases dopamine metabolism. P. PLoS One, 6(9).
Sugden, K. M. (2016). Is Toxoplasma Gondii Infection Related to Brain and Behavior Impairments in Humans? Evidence from a Population-Representative Birth Cohort. PLoS One, 11(2).
Torrey, E. Y. (2003). Toxoplasma gondii and Schizophrenia. Emergent Infectious Diseases, Nov.

About the author:
Marta Browne is an integrative naturopath and parasitologist in South East Queensland.

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