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Scientists find parasites in dead marine mammals

SEATTLE – Two kinds of parasites typically found in cats and opossums have been detected in marine mammals that died in the Pacific Northwest, according to a federal study released Tuesday.

Toxoplasma gondii and sarcocystis neurona were found in most of the animals, even healthy ones, according to scientists with the National Institutes of Health. They studied tissue samples from 161 seals, sea lions, northern sea otters and other marine mammals collected in Washington, Oregon and southern British Columbia from 2004 to 2009.

Toxoplasma gondii, which caused a large outbreak of disease in humans in 1995, enters water through infected cat feces. Sarcocystis neurona is believed to have been introduced in the Northwest by opossums, which can shed an infectious form of the parasite in their feces.

Researchers found that marine mammals infected with both were more likely to have severe brain swelling and die than those infected with just one parasite.

Identifying the link between these parasites and marine mammals could inform public policy decisions, such as managing populations of feral cats and opossums or reducing runoff into coastal waters, said Michael Grigg, the study’s lead researcher and who is with National Institute of Allergy and Infectious Diseases.

“The public health message here is that people can easily avoid the parasites by filtering or boiling untreated water,” Grigg said. “Limiting serious disease in marine mammals, however, will require larger conservation efforts to block these land pathogens from flowing into our coastal waters.”

Researchers in Washington state and Canada also contributed to the study. Necropsies were performed on 151 stranded marine mammals, as well as 10 healthy adult California sea lions that were euthanized to protect Columbia River fish stocks.

The uptick in sarcocystis neurona infections was unexpected, Grigg said, adding that opossums are expanding their range into the Northwest.

“It’s surprising that the number of animals tested came up positive for at least something,” said Dyanna Lambourn, a marine mammal biologist with the Washington State Department of Fish and Wildlife and a study co-author.

“Not every animal out there is dying from these protozoal infections, but it is something that, especially during this time of this year, we see quite a number of animals that are stranding with symptoms associated with these parasites,” Lambourn said.



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