The reason is a microscopic organism called Toxoplasma gondii. This protozoan has been linked in humans to congenital birth defects and nervous system damage. There’s evidence that it’s also tied to an increased risk for psychiatric illnesses, rheumatoid arthritis and other conditions.
It reproduces in cats, which shed parasites in their feces. These oocysts can then be picked up by birds, mice or people.
Cats produce 1.2 million metric tons of waste outdoors each year in the U.S. And about 1 percent of cats are likely shedding Toxo at any given time.
Backyard surveys have found up to 400 Toxo oocysts per square foot. They can survive for more than a year and a half in the soil. And just one—which can be accidentally inhaled or ingested—could start an infection. These stats are in a report in the journal Trends in Parasitology. [E. Fuller Torrey and Robert H. Yolken, Toxoplasma oocysts as a public health problem]
Indoor-only cats are less likely to pick up the parasite. Nevertheless, best to be cautious when around the garden box, sandbox and litter box.
–Katherine Harmon
