Biodiversity May Mean Less Lyme Disease

People who value biodiversity often point to the potential for new medicinals or an ecosystem's greater ability to recover quickly from a disaster. Now researchers have found a specific health benefit of high diversity of small mammals and lizards: It may cut down on the risk of Lyme disease.

Lyme disease is carried by Ixodes ticks. They pick up the disease-causing bacterium when they suck blood from a host. However, only a few species of animals have been shown to effectively transmit the Lyme disease bacterium to ticks. In the eastern United States, for example, white-footed mice are the principal natural reservoir of the bacterium; if infected, the mice pass the disease on to almost all the ticks that feed on them.

Yet this fact presents a puzzle. Richard Ostfeld, a community ecologist at the Institute of Ecosystem Studies in Millbrook, New York, and ecologist Felicia Keesing of Bard College in Annandale-on-Hudson, New York, knew that in some parts of the East Coast, as many as 50% of ticks carry Lyme disease, while in others only about 5% are infected. Why? Ostfeld and Keesing suspected that ticks that encounter a smorgasbord of possible hosts stand a lower chance of picking up the bacterium. To find out, they compared the incidence of Lyme disease in nine regions of the eastern United States to the number of species of small mammals and lizards (typical Ixodes tick victims) in those regions. As the number of species increased, the number of cases of human Lyme disease reported per capita decreased, they report in the June Conservation Biology.

James Mills, a disease ecologist at the U.S. Centers for Disease Control and Prevention in Atlanta, calls the idea that Lyme disease is "diluted" in a biodiverse area a "tantalizing hypothesis" that needs to be tested further. And community ecologist Robert Parmenter of the University of New Mexico, Albuquerque, says the study demonstrates that considering the entire ecological community, not just the disease-carrying organisms, is important for understanding disease transmission.