Feces, specifically from outdoor cats and wild possums, are the culprit in some severe and unusual marine mammal deaths.
Despite the continued online popularity of the videoed interaction between a nuzzling cat and curious dolphin, scientists are pointing out that the intersection between the two species could be having a catastrophic effect on the marine mammals.
A disturbing trend was found in a six-year study that monitored marine mammals in the Pacific Northwest. More than 5,000 dead marine mammals (dolphins, porpoises, sea otters, seals, sea lions and three species of whale) were observed, many of them suffering from encephalitis (brain swelling) long associated with Toxoplasma gondii, a single-celled parasite. The study was published by the National Institutes of Health in 2011.
The issue at hand is the feces from outdoor cats. The waste product contains T. gondii, a parasite that live its entire life cycle inside a cat. T. gondii also is happy enough in other animals, including humans and, as noted, marine mammals.
According to Scientific American, up to one-quarter of people in the U.S. house the parasite, and it is the reason why women are warned against cleaning cat litter boxes while pregnant (the parasite can cause birth defects).
T. gondii is entering the marine environment through a number of channels, including cat owners flushing cat feces down the toilet and feces being washed from soil into waterways that then flow to the ocean.
"Chlorination does not kill T. gondii, but filtration eliminates them from the water supply," notes Dr. Michael Grigg, lead researcher of the study. "The public health message here is that people can easily avoid the parasites by filtering or boiling untreated water. Limiting serious disease in marine mammals, however, will require larger conservation efforts to block these land pathogens from flowing into our coastal waters."
Although the T. gondii parasite has been a known factor in the environment for many years, it has been made more lethal by teaming up with another parasite found typically in Virginia opossums, Sarcocyctis neurona. The opossums, displaced from their native homes by humans in the 1900s, thrived along the Pacific coast all the way up into British Columbia.
With opossums shedding the S. neurona parasite in their scat, and a few good winter storms washing topsoil into waterways, the two related parasites set up a perfect storm of disease transmission for unsuspecting marine wildlife. Researchers found that while the T. gondii often cause long-term, low-grade infection alone, coupled with S. neurona, the result is likely more lethal.
Unfortunately, this leap is becoming more common — enough to have been officially named as "pollutagens" by scientists. The term refers specifically to the crossing of bacteria, fungi and parasites from earth to sea, and the havoc they are wreaking upon the sea creatures.
T. gondii is present in about 70 percent of sea otters along the California coast, according to Melissa A. Miller, a researcher at the Marine Wildlife Care and Research Center in Santa Cruz, Calif.
In addition, according to Scientific American, other pollutagens, such as a strain of Salmonella Newport, were found in a dead newborn orca on the shores of Ventura County, Calif., in 2010. The Atlantic bottlenose dolphins in South Carolina have been shown to have Staphylococcus aureus, the dreaded superbug MRSA that is so common in hospitals.
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