White-Footed Mice Give Ticks a Free Lunch

In the northern and central parts of the U.S., people are more likely to contract Lyme disease and other tick-borne ailments when white-footed mice are abundant.

Mice are effective at transferring disease-causing pathogens to feeding ticks. And, according to an in-press paper in the journal Ecology, these "super hosts" appear indifferent to larval tick infestations.

Drawing on 16 years of field research performed at the Cary Institute of Ecosystem Studies in Millbrook, New York, the paper found that white-footed mice with hundreds of larval ticks survived just as long as those with only a few ticks. Even more surprising, male mice with large tick loads were more likely to survive during a given season.

Richard Ostfeld, a disease ecologist at the Cary Institute, was among the study's authors. "Our findings were counterintuitive. By definition, ticks are parasites. But tick burdens were not correlated with reductions in white-footed mouse survival or overwintering success, and they didn't slow population growth. It looks like ticks are getting a free lunch."

Conclusions were based on an analysis of 5,587 'capture histories' recorded between 1995 and 2011. Every 3-4 weeks, from the peak of larval tick activity in midsummer until the end of the mouse breeding season in fall, mice were trapped on the Cary Institute's campus. On their first capture, animals were outfitted with ear tags. Each time a mouse was trapped researchers recorded the number of ticks on the animal, as well as other variables like its tag ID and sex.

Source: Eurekalert