Study: Toxoplasmosis Contaminating Central Illinois Waterways

The study, conducted by researchers at the University of Illinois, assessed risk factors for Toxoplasma gondii exposure in semiaquatic mammals.

University of Illinois graduate student Adam Ahlers, left, veterinary clinical medicine professor Mark Mitchell and their colleagues found toxoplasmosis in wild minks and muskrats in central Illinois.

L. Brian Stauffer

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Toxoplasmosis is moving rapidly through central Illinois’ landscape and contaminating local waterways, according to a new study conducted by researchers at the University of Illinois.

The study, published online in the Journal of Wildlife Diseases in January, assessed risk factors for Toxoplasma gondii exposure in muskrats and American mink—both semiaquatic mammals—in east-central Illinois.

The agricultural region has extensive drainage systems that could potentially transport T. gondii oocysts into the watershed, according to the study. The researchers used muskrats and American mink as sentinels of watershed contamination.

“We thought we’d do a broad prevalence survey in minks and muskrats,” said University of Illinois graduate student Adam Ahlers, who led the study with veterinary clinical medicine professor Mark Mitchell, DVM, Ph.D., Illinois Natural History Survey mammalian ecologist Edward Heske, Ph.D., and natural resources and environmental sciences professor Robert Schooley, Ph.D. “And when we got the data back, we were really surprised because the prevalence rates were higher than expected.”

The researchers found antibodies for T. gondii in 18 of 30 muskrats and 20 of 26 minks. Infection rates were ≥1.7 times higher than those typical for mammals in upland habitats in this region, according to the study.

The researchers suspected that the widespread use of tile drainage systems and the lack of natural wetlands in central Illinois would help spread the disease, the university noted.

“A lot of streams have been dredged and straightened, and animals that have to live in those habitats are exposed to increased drainage from agricultural and urban runoff,” Ahlers said.

With no wetlands to filter out pathogens such as the T. gondii oocyts, rainwater likely flushes the parasite directly through drainage tiles and into waterways, Ahlers further noted.

“Our hypothesis was that animals positioned in larger watersheds would be exposed to more drainage and more oocysts, so they should have higher toxoplasmosis prevalence rates,” Ahlers said.

The study revealed this to be true for muskrats but not so with minks. This may be due, in part, according to the university, to the already-high prevalence rate in minks.

“Minks have larger home ranges,”Ahlers said. “They leave the stream system and they’re eating mice and birds and other animals that could have the disease. Muskrats are always in the stream channel and are picking up the disease passively—probably through grooming or drinking water. They’re herbivores, so it’s also likely they’re picking it up by consuming oocysts attached to aquatic vegetation.”

Because the majority of the study area was devoted to agricultural production and urbanization, transport of T. gondii into freshwater ecosystems is likely facilitated by modified drainage practices common in these areas, according to the study.

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