By Elizabeth Landau, CNN
VANCOUVER, British Columbia — There’s more to cat excrement than meets the eye, and it may have the potential to cause disease in sea otters and humans alike.
A young cat can shed up to 100 million oocysts – little egg-like structures – in its feces. All it takes is one oocyst to cause an infection of Toxoplasma gondii.
Largely, the parasite is asymptomatic in humans, but it can sometimes cause problems for infants born to infected mothers – including hearing loss, mental disability and blindness. People with compromised immune systems, especially those who have HIV/AIDS, may also develop serious complications.
Researchers are trying to understand why marine mammals in the Pacific Northwest started dying of protozoal diseases starting in 2000; before then, there weren’t any documented cases, but samples from the Pacific Northwest have found a rate of about 4% of protozoal disease among stranded animals, says Michael Grigg, investigator at the National Institutes of Health.
Grigg and other experts discussed these issues Sunday at the American Association for the Advancement of Science (AAAS) annual meeting in Vancouver.
Cat feces may be part of the explanation, the scientists said.
When humans settle near shorelines, that can accentuate land-to-sea pollution. The toxoplasma gondii oocysts from cats can get into the ocean through storm runoff. From there, it can get into mussels and other bivalves that sea otters eat, for example. Humans who eat raw shellfish may likewise be at risk.
Up to 25% of Americans are infected with toxoplasmosis, and in some parts of Europe it’s as much as 50%, Grigg said. Humans carry it throughout their lives. It’s not known why there are more people who have the infection in Europe, although dietary habits (eating raw meat/fish) be a factor.
There are also strains of this parasite in nature in French Guiana and Suriname that are lethal to people, Grigg said.
Over the past few years, scientists have been investigating a new form of Toxoplasma gondii ominously called Type X. It was first discovered in sea otters, and it’s a combination of the familiar Type II strain and a unique strain of the parasite. It’s unclear whether Type X is more serious than Type II, but Type X represents about 40% of infections.
In the few cases where Type X has been found in humans, it was problematic, but there were other immune system compromising factors – one patient was elderly, and one had had a transplant of some kind, Grigg said.
Toxoplasma gondii oocysts can’t be destroyed with ultraviolet light or chlorine bleach – only freezing or boiling can kill them, Grigg said. For instance, there was a big outbreak in 1995 in Victoria, British Columbia, likely because the municipal water system was using unfiltered water.
Not all cats have toxoplasmosis, but a large majority do get infected, Grigg said. And they only secrete oocysts when they’re young. But if 10% of the 86 million cats owned as pets in the U.S. were infected, that’s still a whole lot of little parasite-infecting eggs.
That doesn’t mean you shouldn’t eat shellfish at all. Pay attention to to where it’s harvested and when, says Melissa Miller of the Marine Wildlife Veterinary Care and Research Center in California. But there could be issues with raw or undercooked foods of all kinds, including shellfish. “There’s far more that we don’t know than we know,” she told reporters.
There’s ongoing research into a Toxoplasma gondii vaccine for cats, although one is not available yet.
In the meantime, you can take some precautions to prevent parasites from your cat’s litter from getting into the water. Miller says she picks out the poop from the litter box and puts it into plastic bags and sends it to an approved landfill. Miller says she also keeps her cats indoors.
And even though parasites can recombine into different parasites, Grigg says we shouldn’t be worried about a new toxoplasma parasite that’s truly catastrophic to the human species.
“What we would expect is that nature will sort out what’s the right fit, the strain that doesn’t cause too much disease and can be maintained in nature,” Grigg told CNN. “I don’t think there’s some big pathogenic strain that’s going to emerge and kill a lot of people.”