SANTA CRUZ (January 2010) - Organic gardeners know that many types of manure are good for garden soil. We add cow, horse, chicken and even bat manure to our yards, knowing that the breakdown of these products feeds both the soil and the vegetables in our gardens.
Cat manure, on the other hand, should never be added to garden compost or left to decompose in vegetable beds. Cat feces frequently carry parasites that can infect humans, and should be excluded from the garden or removed as promptly as possible.
It is commonly known that pregnant women should avoid cat waste to prevent infection with Toxoplasmosis, a disease that can cause devastating birth defects if contracted during gestation. But Toxoplasmosis, and other diseases spread by cat waste, can infect anyone who comes into contact with contaminated garden soil, and gardeners should take precautions to avoid a possible lifelong infection.
Toxoplasmosis is caused by a single-celled protozoan parasite called Toxoplasma gondii, one of the most common parasitic diseases of warm-blooded animals. While Toxoplasma can infect numerous species, it will only reproduce in the intestines of an infected cat, including wild cats such as mountain lions.
Humans are considered an ‘intermediate’ host for Toxoplasma, meaning that our bodies can be infected by the parasite, but we cannot spread it to other creatures (unless they eat an uncooked, infected human, a fortunately rare occurrence.)
But once a human is infected with Toxoplasma, the parasite migrates deep into our tissues - frequently the tissues of the brain and the eyes - creates small cysts, and stays there for life, multiplying slowly as the years pass.
Most people infected with Toxoplasma are seemingly unaffected by the organism, never notice symptoms, and are never diagnosed. But trouble can arise later in life if an infected person contracts AIDS, or undergoes organ transplantation or chemotherapy for cancer. When a person’s immune system is depressed by disease or medical treatment, Toxoplasma can erupt from dormancy to fatal effect.
An estimated 750 people die of Toxoplasma infection in the U.S. every year, many of them AIDS patients, according to the Centers for Disease Control. The agency also estimates that 400 to 4,000 U.S. infants are congenitally infected with the disease every year.
About half of the Toxoplasma deaths in the U.S. are the result of eating raw or undercooked meat, according to the CDC. (Like humans, mammals such as cows, pigs and sheep are intermediate hosts of the Toxoplasma organism.) The other fatal infections are though to be caused by environmental and gestational exposure.
Gardeners and agricultural workers are at risk through their exposure to Toxoplasma-contaminated soil. Cats bury their feces in the soil, and the feces of an infected cat can carry millions of Toxoplasma eggs, which can survive in the environment for more than a year.
Toxoplasma is contracted when the eggs are swallowed, either hidden on poorly washed produce or carried by unwashed hands.
Cat feces can also contaminate the soil with roundworms, hookworms and tapeworms, all of which are transmissible to humans, either by directly penetrating the skin (roundworms and hookworms), or by ingesting the eggs or larvae via unwashed hands or produce (roundworms, hookworms, and tapeworms).
The good news is that roundworm, hookworm and tapeworm infections are treatable, and Toxoplasmosis is usually asymptomatic. In addition, rates of Toxoplasma infection in the U.S. have been trending downward in recent years.
The vast majority of infections are easily avoidable through simple sanitation. Gardeners can prevent exposure by wearing gloves, excluding cats from food growing areas, and promptly cleaning up feces when necessary.
Garden produce should also be thoroughly washed and rinsed before eating. Cooking will kill the Toxoplasma organism. Hands should be thoroughly washed after work or play in the garden.
And cat owners can do their part by providing litter boxes for their animals, and policing their yards.