Lyme disease, caused by the spirochaete bacterium Borrelia burdoferi, has acquired notoriety in the United States and wilder parts of Europe. It is transmitted by blood-sucking ticks, usually among deer and small mammals. But Ixodes ticks are not fussy and will feed on any vertebrate, including humans. As human activities encroach into wooded and heathland environments, we run the risk of tick infestation and possible Lyme disease transmission. For 13 years, Ostfeld et al. looked at the environmental parameters that might predict how severe the upcoming Lyme season might be. Classically, deer abundance and weather were thought to influence numbers of ticks and hence predict the risk of human infection, but it turns out that small mammal abundance over the previous year is a much better indicator. Mice and chipmunks, whose numbers are determined by food supply in the prior year, are important hosts for the tiny juvenile stages of the ticks, which, because they are unnoticeable, tend not to be removed from the skin and can be extremely abundant in summer. Consequently, the acorn supply for mice and chipmunks 2 years previously makes an excellent measure of Lyme disease risk. -- CA
PLoS Biol. 4, e145 (2006).
