A $1.86 million grant from the National Science Foundation – National Institutes of Health Ecology of Infectious Disease Grant Program will expand the investigations of a UC Davis-led research team tracking how a deadly parasite moves from land to sea to infect and kill sea otters (Enhydra lutris nereis) in California.
"We've already identified the single-celled parasite, Toxoplasma gondii, that causes high rates of mortality in threatened southern sea otters," says Patricia Conrad, professor of parasitology at the UC Davis School of Veterinary Medicine. Conrad, the principal investigator, says, "Toxoplasma infections are killing southern sea otters and are one of several factors reducing the potential for sea otter population recovery." Sea otters do not prey on known intermediate hosts for T. gondii, says Conrad, so the most likely source of infection is highly infectious, egg-like oocysts shed in the feces of cats and transported via freshwater runoff into the marine ecosystem.
Toxoplasma gondii can also cause serious disease in pregnant or immuno-compromised people. Sea otters serve as sentinels of the parasite since they share the same environment and consume some of the same foods as humans.
The funding supports a multi-institutional collaboration, with scientists from UC Santa Cruz, the California Department of Fish and Game, the University of British Columbia, CSU Fresno, and the Institute of Ecosystem Studies working with UC Davis investigators in the Wildlife Health Center, Bodega Marine Laboratory and the Center for Animal Disease Modeling and Surveillance.
Investigating the transmission of T. gondii in sea otters may offer the best opportunity to understand how such parasites flow from land into the marine ecosystem. The research team will focus on three aspects of transmission:
§ Terrestrial ecology—Researchers will survey cat owners to learn more about the numbers of domestic and feral cats and how they are managed in these high-risk areas for sea otter infection. In addition, the surveyors are sampling wild rodents to determine if they are infected with T. gondii parasites and may serve as a source of the infection for cats. A pilot study of toxoplasma infection in wild rodents from the Morro Bay was funded by the Morro Bay National Estuary Program.
§ Land-runoff ecology— To understand how T. gondii moves from terrestrial hosts to the near-shore habitat of southern sea otters, scientists will observe the zones and patterns of runoff from land into coastal waters; they will create models to assess how T. gondii oocysts travel through water into the sea where sea otters live.
§ Sea otter ecology— A team of wildlife veterinarians and ecologists will assess behavioral and dietary risk factors for parasite exposure in a group of sea otters closely monitored between 1999 and 2003 by UC Santa Cruz, the US Geologic Survey, and the California Department of Fish and Game.
Studies emphasize two sites, Elkhorn Slough and Morro Bay, where notable sea otter infections and deaths have been reported. Once the data have been gathered and analyzed, scientists will develop simulation models to assess how well various strategies to reduce T. gondii in sea otters affect their risk of exposure. The project ends in 2008.
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