Chipmunks And Shrews, Not Just Mice, Harbor Lyme Disease

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Chipmunks And Shrews, Not Just Mice, Harbor Lyme Disease

_http://www.sciencedaily.com/releases/2007/11/071129183745.htm_

(http://www.sciencedaily.com/releases/2007/11/071129183745.htm)

 

 

ScienceDaily (Dec. 6, 2007) — A study led by a University of Pennsylvania

biologist in the tick-infested woods of the Hudson Valley is challenging

the widely held belief that mice are the main animal reservoir for Lyme

disease in the U.S.

 

 

The paper demonstrates that chipmunks and two shrew species, not just

mice, are the four species that account for major outbreaks.

According to the study, white-footed mice account for about a quarter of

infected ticks. Short-tailed shrews and masked shrews were responsible for a

quarter each and chipmunks for as much as 13 percent. According to the

team, vaccination strategies aimed solely at mice are unlikely to bring the

disease under control. Efforts to control Lyme disease and prevent its

spread, the team said, must include strategies that account for multi-species

carriers.

**The majority of zoonotic diseases, those that can be transmitted from

wild or domestic animals to humans, are generally assumed to have one natural

animal host,†Dustin Brisson, professor of biology in the School of Arts

and Science at Penn, said. “For Lyme disease, this host has been the

white-footed mouse. Data are beginning to accumulate to suggest that the story

is

much more complex, mice being one of an assemblage of vertebrate species

contributing to feeding ticks and transmitting B. burgdorferi. Deer, a

popular culprit of the Lyme disease epidemic, play a rather minor role in

transmitting the bacteria to feeding ticks, although they are a major cause of

the

elevated tick densities that are important for the spread of the disease to

humans.**

Borrelia burgdorferi sensu stricto, the bacterium that causes Lyme

disease, is transmitted to humans by infected, blacklegged ticks. The ticks,

infected as larvae during their first meal — the blood of a vertebrate —

are

middle men.

Mice were thought to be the primary natural reservoir of the disease

because nearly 90 percent of ticks feeding on an infected mouse contract the

disease, nearly twice as much as any other species. In addition, mice are

common, conspicuous and easy to research in the field and in the lab, promoting

their status as primary natural reservoir. Yet other factors, such as

population densities and tick burdens of other disease-carrying species, led

investigators to rethink mice as the principal reservoir species for the

disease.

The team employed genetic and ecological data, including dynamics of an

outer surface protein of Lyme disease that provides clues about how the

disease was transmitted, to discover that mice feed only 10 percent of all

ticks

and 25 percent of B. burgdorferi-infected ticks in the northeastern Lyme

disease endemic zone. Shrews feed 35 percent of all ticks and 55 percent of

infected ticks.

Emerging zoonotic pathogens, the 132 infectious diseases that cross the

line between animal and human species, like Lyme disease, are a constant

threat to world health. The research team, focused on improving existing

strategies to protect the public health, is promoting the notion that targeting

a

single host species, in this case the white-footed mouse, may have been a

faulty assumption.

While public-health strategies to control Lyme disease in North America

have focused on interrupting transmission between blacklegged ticks and

white-footed mice, Lyme disease infects more than a dozen vertebrate species,

any of which can infect feeding ticks and increase human Lyme disease risk.

The research was performed by Brisson of the Department of Biology at

Penn, Daniel E. Dykhuizen of Stony Brook University and Richard Ostfeld of the

Institute of Ecosystem Studies. It was supported by the U.S. Public Health

Service, the National Institutes of Health and the National Science

Foundation.

This research was published in the Proceedings of the Royal Society B.