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.