People are less likely to get Lyme disease if they live in areas with a greater diversity of small mammals, according to the June issue of Conservation Biology. This is the first study showing that biodiversity may reduce the risk of disease in people. Caused by a spirochete bacterium, Lyme disease is transmitted by ixodid ticks. The disease can cause a characteristic skin rash, flu-like symptoms, arthritis and neurological damage. In part because the disease can be difficult to diagnose and a recently-approved vaccine is not completely effective, the best safeguard against Lyme disease is to avoid ticks.
Many ticks never become infected because some hosts transmit the bacteria inefficiently.
In North America, the host that transmits the bacteria most efficiently is the white-footed mouse. Ostfeld and Keesing hypothesized that an area with more biodiversity would have a greater number of inefficient host species, which would mean fewer infected tick nymphs and thus fewer cases of Lyme disease in people. These results are supported by the finding that the incidence of Lyme disease falls in East Coast areas with a greater diversity of small mammals. Ostfeld and Keesing suggest that decreasing the forests' fragmentation might also decrease the local incidence of Lyme disease. Increased biodiversity could also reduce the risk of the many other vector-borne diseases, which include plague, West Nile encephalitis and leishmaniasis.