Outdoor cats may be a threat to sea otters.
Toxoplasma gondii is a microscopic parasite of mammals. It is capable of infesting a wide variety of hosts. However, it is only capable of completing its lifecycle and reproducing in cats.
In cats, Toxoplasma rarely causes illness. Most experts believe that cats can contract the parasite only once in their life. They then shed Toxoplasma in their feces for approximately three weeks.
To reiterate, the prevailing theory is that each cat sheds Toxoplasma for a maximum of three weeks during its life, and the parasite rarely makes cats sick. It doesn’t sound like Toxoplasma would be dangerous. But it can be.
For starters, Toxoplasma can infect people. For most people, the parasite doesn’t pose much of a risk. However, under the right circumstances, Toxoplasma can be very dangerous indeed. If a woman is exposed to the parasite during pregnancy, birth defects or miscarriage may result. If someone with a compromised immune system is exposed to Toxoplasma, he or she may fall ill or even die.
It is noteworthy that, according to experts, most people who contract Toxoplasma do not catch the disease from their cat. People appear to be more likely to be exposed to Toxoplasma by eating undercooked meat or shellfish.
The parasite is very durable and can live for many months in soil. Unwashed vegetables, especially those that come from gardens where cats may defecate, are another source of human infection.
Toxoplasma’s ability to survive for long periods in soil may be contributing to yet another crisis. Scientists believe that Toxoplama is killing California sea otters.
The Journal of the American Veterinary Medical Association reports in its December 1, 2007 issue that Toxoplasma in coastal soil may be washing into the ocean, where it is infecting, and ultimately killing, sea otters.
Feral cats are the most likely source of the parasite, but experts believe house cats that defecate outside may be contributing to the problem. If you live near the coast and you are fond of sea otters, you may want to think twice before you let your cat go outside.
For reference, the studies mentioned in this post are Conrad et al, J Am Vet med Assoc 2007;231:1676 - 1684 and Jessup et al, J Am Vet med Assoc 2007;231:1648-1652.
You have questions. 
Great article about toxoplasmosis but I do have a question: A good friend of mine got toxoplasmosis from bunnies she kept in the house and used a litter box (which, of course, she cleaned out. Are cats the ONLY source?
I’ve heard that flushing used kitty litter is being discouraged in California for this reason, but this doesn’t make any sense to me, as sewer water shouldn’t be going to the ocean, but to a treatment plant. Can anyone shed some light on this?
Are feral cats the reason that dinosauers are extinct?
Suz: If your friend caught Toxoplasma gondii, I doubt she got it from her rabbits. Experts believe that only cats can pass viable organisms in their feces. However, many people who don’t have cats contract the disease by eating unwashed vegetables or undercooked meat.
UglyGerbil: I believe that that a law is pending in California to place warning labels on cat litter packages. The labels would advise against flushing used litter. The goal, I think, is to keep Toxoplasma out of shellfish that sea otters and people eat. Toxoplasma can survive seage treatment.
Thanks for keeping us informed! I’ve been trying to spread the word about how the improper disposal of litter can be threatening sea otters - we love seeing them here along the West coast! Catster rules!
[…] Transmission of these diseases does not occur often. However, talk to your veterinarian about toxoplasmosis and intestinal worms. If you practice good hygiene, take basic precautions and keep your cats free […]