Pet cats spread brain parasite to wildlife, new research finds


Cats sit on a side road in Glendale, Ky.

Cats sit on a side road in Glendale, Ky.
Photo: Timothy D. Easley (PA)

New research shows how cats are likely to be the cause of the spread of a problematic brain parasite to wildlife, and how the continued deterioration of our environment makes this problem even worse.

A to study published in Proceedings of the Royal Society B: Biological Science connects densely populated urban areas with increased cases of Toxoplasma gondii among wild mammals. House cats are common carriers of the parasite, and cats are often allowed to roam free outdoors, so researchers naturally suspect our feline friends are the driving mechanism behind this process. University of British Columbia veterinarian and environmentalist Amy Wilson led the new research.

Toxoplasma gondii is a parasite that causes a very common infection known as toxoplasmosis or toxo; it infects approximately a third of the world’s population. The parasite is known to alter the behavior of mice, making them more susceptible to predation by cats. Once infected, a single cat can throw half a billion poisonous eggs in just two weeks. These eggs, called oocysts, are super tough, able to live in moist soil and water for a full year and maybe even longer.

Scientists refer to the toxo as a generalist zoonotic parasite, which means it is highly capable of living and spreading to all kinds of different animals. For the toxo, that means he can make the jump to any warm-blooded animal, including birds and mammals. For healthy animals, a toxo infection shouldn’t be a problem, but in the presence of a weakened immune system the parasite kicks in, causing all kinds of illness and death in some extreme cases. In humans, the disease is particularly dangerous for Pregnant people.

At the start of the study, Wilson and his colleagues knew that toxo is not distributed evenly among wildlife around the world, but the processes behind this variation were not well understood. The new study was an attempt to fill this knowledge gap. To this end, the team analyzed 45,079 documented cases of toxoid in free-roaming species of wild mammals. These data were taken from 202 international studies and included 238 different mammalian species.

The link became clear: Wild animals living near dense urban areas were more likely to be infected with the toxoid, and it didn’t matter where these animals were in their respective food webs.

“For a species living in an area with high human density, the risk of toxoplasmosis is about three to four times more than for a species living in an area with low human density, ”Wilson wrote in an email to Gizmodo.

The researchers also noticed a higher prevalence of the parasite in warmer climates and in aquatic animals. “Any warm-blooded mammal can be infected, but we found that species in aquatic habitats tended to have higher infections, likely from exposure to contaminated water, ”Wilson said.

However, I have a few caveats to point out.

The researchers did not have the desired global coverage due to a lack of data for Central Eurasia and Central and East Africa. It is unfortunate, because “the countries of these continents have relatively high human numbers T. gondii prevalence ”, according to the document. In addition, the team would like to dig deeper into the various ecosystems studied, to get a more nuanced idea of ​​where and how the toxo could spread in the identified hotspots.

The article identifies areas at high risk for wildlife to acquire toxo-infection, but as the researchers themselves admit, the cause and effect have not been firmly established; scientists are simply inferring that cats are the primary drivers of the disease, which, to be fair, is probably a pretty good inference. As a result, “proactively targeting pathogen pollution in domestic cats would be the most pragmatic and effective intervention to reduce infections in wildlife,” write the authors.

Ooh, that’s such a good term: “pathogenic pollution”. That’s a nice way to describe the problem. We are literally polluting the environment with the toxo parasite by allowing certain cats, a creature shaped by artificial selection processes and now reproducing themselves to incredibly high numbers– to move around freely. It’s good documented that domestic cats, when allowed to roam free, are a ecological threat, killing large numbers of birds and other creatures; we can now add another item to the list, as probable propagators of poison to wildlife.

An important point raised in the document is that dynamic and healthy ecosystems are a natural defense mechanism against the spread of pathogens, toxo included. “Healthy landscapes with different species of vegetation, soil bacteria, and invertebrates work together to filter or inactivate pathogenic organisms, essentially removing them from circulation where they could infect wildlife or humans, ”wrote Wilson in his email.

VSThere are things that conscientious cat owners can do to reduce the spread and exposure to toxinsD. “Absolutely no one needs to relocate their cat—change the litter box every few days and don’t leave your cat outside unattended to hunt wildlife, ”Wilson said. “Cats that kill wildlife are a major conservation problem, but they also increase the risk that a cat will be infected with parasites that they can pass on to wildlife and humans. Importanty, toxoplasmosis is not only a risk for cat owners but for anyone who accidentally comes in contact with something contaminated with the feces of infected cats. For example, researchers find Toxoplasma in the soil of playgrounds and parks, so it’s really a health concern for everyone.

This article has been updated with comments from Amy Wilson.


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