Scientists and researchers have recently discovered a correlation between Toxoplasma gondii and the decrease in the sea otter population off the California Coast. Since cats are the only creatures that shed the T. gondii parasite, through their feces, there seems to be a direct link. Although other causes are also suspect, researchers from UC Davis, in a study of otters who habitated areas near freshwater runoff, found that 42% of live otters and 62% of dead otters tested positive for T gondii. Sea otters are regarded as being "an almost ideal sentinel species," much like the old canaries in mines, in that they telegraph things that might be going on in the larger marine environment, according to David A. Jessup, senior wildlife veterinarian for the California Department of Fish and Game. In addition, injured sea otters offer an easy and attractive meal for sharks, which could (it is presumed) also become infected with the parasite.
What is Toxoplasma Gondii?
T. gondii is a parasite with a two-phase life cycle: intestinal and extraintestinal. In cats, the intestinal phase goes through a process which eventually produces oocysts, which are "shed" in the feces. Human toxoplasmosis can result from exposure to the T. gondii through poor sanitation after handling cat litter; also from working unprotected in a garden which may have T Gondii oocysts in the soil. Toxoplasmosis can also be acquired through handling or eating raw meat or undercooked meat.
Most humans who test positive for T. gondii may never even know they have it. The exceptions are immunocompromised, e.g. HIV+ patients or individuals going through transplants. In people with weakened immune systems, the parasite (through the extraintestinal phase) can migrate to other areas of the body, including the brain, causing severe neurological disorders, including paralysis.
For some reason, sea otters seem to be more susceptible to the extraintestinal phase than "normal" humans. Dr. Jessup comments in an article by The Scientist, "The animals are often found alive and are suffering seizures, showing obvious signs of damage to their brains. They can't hold food and can't take care of themselves, and their eyes are dilated."
How Did T. Gondii Get into the Ocean?
Although no one knows for certain, it is thought that there could be several causes:
- Feral Cat Colonies: In Moss Landing, a port near Monterey, CA, there are 40 or 50 feral cats living under or around the wharf, according to Dr. Jessup. Nearby dairies also attract cats in large numbers.
- Sewage Treatment Plants: These plants traditionally treat sewage to kill harmful bacteria, remove the waste solids, and pump the resultant "safe" effluent directly into a freshwater source that eventually drains into ocean bays. Unfortunately present means of sewage treatment do not kill the T. Gondii parasite. Cat owners using flushable litters, may be unwittingly contributing to the ultimate deaths of sea otters.
- Storm Drain Runoff: Rain, lawn and garden surface water, and anything you manually put into that storm drain in the street near your house eventually runs off into a creek or river which flows directly into an ocean bay. Since outdoor cats bury their feces, deep watering or heavy rains can float the oocysts (which have an extremely hard shell) out to a bay. It is unknown whether the sea otters are ingesting the parasite directly from the water, or by eating contaminated shellfish. Patricia Conrad, a UC Davis parasitologist, is studying the bivalves that are part of sea otters' diet to see if Toxoplasma is concentrating in mussels.
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