3 June 2008
Anchovies A Tasty Entrée Into The Marine World For Toxoplasma Gondii
by Kate Melville
Not content with befuddling the brains of land mammals; the cat parasite Toxoplasma gondii is now making significant inroads into the marine world thanks to the humble anchovy. At least, that's according to researchers at California Polytechnic State University, who have been investigating why marine mammals around the world are succumbing to this canny feline parasite.
T. gondii is a protozoan parasite which causes toxoplasmosis. While the only known reservoir of the infectious form of the parasite (the oocyst) is the cat, the CDC estimates that more than 20 percent of the U.S. population carry the parasite. Human infection rates are much higher in developing countries and scientists continue to debate the subtle effects the parasite may have on humans.
Worryingly, over the past decade, toxoplasma infection has appeared in a variety of sea mammals including beluga whales, dolphins, sea lions and seals. It has also become a major cause of death in Californian sea otters living. It is estimated that approximately 17 percent of sea otter deaths can be attributed to toxoplasma. While many believe fresh water runoff contaminated with cat feces is to blame, there is no definitive evidence on the source of infection.
"The question that drives our research is how are marine mammals from the Arctic Circle to Australia infected by a parasite that is spread primarily through the consumption of infectious cat feces and infected meat? Based on the global prevalence of T. gondii infections, we hypothesize that migratory filter feeders, specifically northern anchovies, are serving to spread T. gondii throughout the ocean," says Gloeta Massie, a graduate student who conducted the research with Associate Professor Michael Black.
To test their hypothesis, Massie and Black exposed northern anchovies to the parasite and then, using molecular techniques, tested for the presence of the parasite within the fish. They detected T. gondii DNA in two-thirds of the exposed fish. Presenting their findings at the 108th General Meeting of the American Society for Microbiology in Boston, the researchers said the next step was to determine the infectivity of exposed anchovies to marine mammals.
"Do our findings mean that you should stop eating anchovy pizza? No. T. gondii oocysts are destroyed by high heat. Unfortunately, marine mammals do not have the option of cooking their food before they eat it. As anchovies are considered prey for practically every major predatory marine fish, mammal and bird, if the exposed anchovies harbor infectious oocysts, this could present a possible transmission path of T. gondii in the marine environment," says Massie.
Source: American Society for Microbiology