Biodiversity may lessen Lyme disease.

The richer a region's array of lizard and small-mammal species, the less likely people are to catch Lyme disease, say New York researchers.

That's the pattern emerging from an 11-state area, say Richard S. Ostfeld of the Institute of Ecosystem Studies in Millbrook and Felicia Keesing of Siena College in Loudonville. The trend could provide a new reason to love biodiversity--it protects human health--they say in the June CONSERVATION BIOLOGY.

The U.S. government logs between 12,000 and 17,000 cases of Lyme disease a year, making it the most common insect-borne disease in the United States. At least two species of Ixodes ticks spread it when they bite. The ticks typically hatch uninfected, but as they take one blood meal during each of their three later life stages, the ticks pick up bacteria.

Only some of the 100 or so species that ticks bite can easily infect them with bacteria. The white-footed mouse, a common species, transfers the disease exceptionally well. An abundance of other tick targets could dilute the concentration of such dangerously good infectors and thus slow disease spread, the researchers suggest.

Small-mammal diversity ranged from 26 species in Maine, with some 50 Lyme cases per 100,000 residents, to 38 species in Georgia, which reported fewer than 5 cases per 100,000. Maine has no native lizards, but Georgia has 14.