Forty Percent of River Otters in England and Wales May Be Infected with Parasitic Disease Toxoplasmosis

Eurasian otter by Catherine Trigg

Eurasian otter by Catherine Trigg

(Washington, D.C., July 11, 2013) A study by 11 British scientists who examined 271 Eurasian otter cadavers across England found that 108 (almost 40 percent) of those animals tested positive for the parasitic disease toxoplasmosis, which is described in the study as a “globally important [disease] with potentially devastating health impacts both for humans and a range of domestic and wild species.”

The study was peer-reviewed and published in the online journal Parasites and Vectors earlier in 2013.

“The relatively high prevalence of [the toxoplasmosis parasite] in a predominantly [fish-eating] freshwater mammal suggests widespread faecal contamination of freshwater ecosystems,” the report said. It is the first widespread study of the toxoplasmosis parasite in UK wildlife and the first such extensive study of it in Eurasian otters, which are described as a sentinel species of fresh water, reflecting the overall health of these ecosystems.

The toxoplasmosis parasite has, for many years, been considered to be more terrestrial in nature and impact, but several reports have indicated significant infections in a range of both marine and freshwater species. Previous reports also link toxoplasmosis to deaths of Hawaiian monk seals, deaths of Pacific Coast otters, and infections in 75 captive marine mammals from four facilities in southern and central regions in Mexico.

None of the otter cadavers that were examined for the British study died directly from toxoplasmosis. The leading causes of mortality were road traffic (90 percent); infection, fighting injuries, and/or emaciation (5.5 percent); or drowning or shooting (2.6 percent). The study's authors pointed out, however, the comparative ease of finding road-killed otters as opposed to those which might have actually died from toxoplasmosis.

Individuals become infected either by ingesting a form of the parasite that is excreted in the feces of cats (which the report described as “the definitive host”  – meaning that cats are the only host species in which the parasite can sexually reproduce) and finds its way into water or soil from uncooked meat of infected animals, or through congenital transfer.

“This research was made possible through a long-term programme of carcass collection, aided by members of the public. It highlights the valuable insights that can be gained through organised collection of wildlife found dead on the roads,” said Elizabeth Chadwick, lead author of the study.

Toxoplasmosis is a serious issue in the United States, where there are about 80 million feral cats. Studies show that 60 to 80 percent of them carry the toxoplasmosis parasite, which they shed via their feces, releasing hundreds of millions of infectious oocysts that remain viable for many months. In addition to posing a human health hazard in the U.S., outdoor cats have also been found to pose a mortal threat to scores of wildlife, with studies indicating they are the single greatest source of human-caused mortality for birds and mammals. Those studies estimate that outdoor cats kill 1.4 to 3.7 billion birds and 6.9 to 20.7 billion mammals.

“Feral and free-ranging cats effectively contaminate the environment wherever they defecate, increasing the likelihood of transmission to wildlife, pets, and people,” said Grant Sizemore, American Bird Conservancy's Cats Indoors Program Officer. “If there are cats roaming in your neighborhood, you are potentially at risk of contracting this parasitic disease.”

More than 60 million men, women, and children in the United States carry the toxoplasmosis parasite. Although most lack noticeable symptoms, women newly infected during pregnancy, and anyone with a compromised immune system, should be aware that toxoplasmosis can have severe consequences. Furthermore, infection may increase the risk of schizophrenia, autism, Alzheimer's, Parkinson's disease, obsessive compulsive disorder, bipolar disorder, and other afflictions.

Toxoplasmosis is one of a group of five parasitic diseases that have been targeted by the Centers for Disease Control and Prevention (CDC) for public health action. The CDC says that if a woman is pregnant and becomes newly infected with toxoplasmosis during or just before pregnancy, she can pass the infection to her unborn baby, potentially causing:

Infants infected before birth often show no symptoms at birth but may develop problems such as vision loss, mental disability, and seizures later in life.

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