A recent paper examined 45,079 cases of toxoplasmosis in wild mammals—a disease that has been linked to nervous system disorders, cancers and other debilitating chronic conditions—using data from 202 global studies and found wildlife living near dense urban areas, where there are lots of cats carrying the pararsite, were more likely to be infected.

One infected cat can excrete as many as 500 million Toxoplasma oocysts (or eggs) in just two weeks. The oocysts can then live for years in soil and water with the potential to infect any bird or mammal, including humans. Toxoplasmosis is particularly dangerous for pregnant women.

If an animal is healthy, the parasite remains dormant and rarely causes direct harm. However, if an animal’s immune system is compromised, the parasite can trigger illness and potentially death.

What would help? Limiting the number of cats allowed to roam free would be the big improvement. Forests, streams and other ecosystems can filter out dangerous pathogens like Toxoplasma, but those will not be found in cities, and in order to combat climate change and economic stress, experts recommend urban living where fewer resources are needed per person.

Citation: Wilson Amy G., Wilson Scott, Alavi Niloofar and Lapen David R. 2021Human density is associated with the increased prevalence of a generalist zoonotic parasite in mammalian wildlifeProc. R. Soc. B.2882021172420211724 http://doi.org/10.1098/rspb.2021.1724