Ticks had few measurable effects on white-footed mouse survival

(Millbrook, NY) People living in northern and central parts of the U.S. 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.”

Lead author Michelle Hersh, a past Cary Institute postdoctoral researcher, is now at Sarah Lawrence College. “White-footed mice are reservoirs for the agents that cause Lyme disease, anaplasmosis, and babesiosis. Larval blacklegged ticks can become infected when they feed on mice. These ticks can then transmit illness to people during their next blood meal.”

Understanding the ecology of tick-borne illness is essential to human health.

Prior Cary Institute research revealed a positive relationship between white-footed mouse numbers and the abundance of blacklegged ticks infected with the bacterium that causes Lyme disease. But little was known about the impact that feeding larval ticks had on white-footed mouse survival.

Co-author Shannon LaDeau, also a disease ecologist at the Cary Institute, concludes, “Our findings underscore the importance of mice as reservoirs for tick-borne pathogens. From a human health perspective, the indifference that white-footed mice have to blacklegged ticks is bad news. It signals a positive feedback loop that favors the proliferation of parasites.”



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