Toxoplasmosis in wild animals is more common in places of higher human density

A study has found that the protozoan parasitic disease called toxoplasmosis is more commonly found in wild animals that live near or in humanly dense urban areas. The chain of events is the obvious one namely that the domestic cat is the primary vector for toxoplasmosis because the domestic cat sheds toxoplasma gondii (T. gondii) oocysts in their faeces. And where there are domestic cat wandering around outside, interactions with wild animals is likely to transmit the disease to them (zoonotic disease). On a personal level, I would expect, too, that coyotes which frequently attack and eat domestic cats, would also acquire toxoplasmosis because of the toxoplasma gondii oocysts inside the tissues of the domestic cat. Thirty to fifty percent of the human population is currently infected by the parasite, usually asymptomatically. Please read: Truth about Toxoplasmosis and Cats for an objective appraisal.

Map showing where T. gondii is most prevalent in wild animals
CLICK ON THE IMAGE FOR A LARGER MORE READABLE VERSION. Figure 1. Distribution of study sites included in the global analysis of Toxoplasma gondii prevalence data for free-ranging wild mammal populations. Source: theb study as stated at the base of the page.
Two useful tags. Click either to see the articles:- Toxic to cats | Dangers to cats

So where there are more people in dense urban areas there are more domestic cats outside and where there are more domestic cats outside there is a greater possibility to transmit toxoplasmosis to wild animals. It’s a simple formula.

The study conducted by Amy G Wilson et al. also concluded that there was support in their findings that T gondii prevalence is influenced by climate. They found that this protozoan disease was more likely to thrive in warmer locations – “T. gondii prevalence increased in warmer locations”. They argued that the higher temperature may influence prevalence through both ‘variation in oocyst survival and host distribution’.

Also, they found that there was a greater prevalence of toxoplasmosis in aquatic mammals compared to terrestrial species. My thought: it is likely that aquatic animals are exposed to oocysts transferred from cats I guess living near watercourses and rivers et cetera. I wonder, too, whether the modern habit of flushing cat faeces down a human toilet can contribute to the spread of toxoplasmosis in aquatic creatures. Certainly there was a report years ago of sea otters and Beluga whales off the coast of California contracting the disease because of human waste and cat waste getting into the sea.

By evolutionary bad luck, toxoplasmosis is a constant cloud hanging over the domestic cat. It is a disease which the anti-cat brigade latch onto to criticise the domestic cat and in particular allowing the domestic cat to roam outside the home freely. There has always been a strong argument to keep cats indoors and that argument is growing. It is an argument which is being taken up by more cat owners. However, in a study in the UK it was found that if people keep their cats inside is because they want to protect their cat from loss, injury or death. The decision is not made to protect wildlife.

It is the scientists and the ornithologists who campaign and lobby legislatures to make full-time indoor cats mandatory to protect wildlife from predation by cats. This study will add to the reasons.

The study: Human density is associated with the increased prevalence of a generalist zoonotic parasite in mammalian wildlife by Amy G. Wilson, Scott Wilson, Niloofar Alavi and David R. Lapen. They analysed 45,079 cases of toxoplasmosis in 238 species of wild mammals from 202 published studies. It is published on the Proceedings of the Royal Society B website.


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