Century-Old Dead Mice May Hold Key to History of Lyme Disease

Editor’s Note: Photos courtesy of Virginia Museum of Natural History and North Carolina Museum of Natural Sciences.

UNIVERSITY OF RICHMOND — University of Richmond biology professor Jory Brinkerhoff led a team studying hundreds of old dead mice to research the history of Lyme disease in Virginia and North Carolina.

The white-footed mice were part of collections from two museums — Virginia Museum of Natural History and North Carolina Museum of Natural Sciences — that have thousands of specimens, preserved as dried skins and skeletons, from native mammals. Some specimens were collected and placed in storage more than a hundred years ago.

Brinkerhoff, a disease ecologist who specializes in the study of tick-borne illnesses, partnered with Nancy Moncrief, curator of mammalogy from VMNH, and Lisa Gatens, collections manager from NCMNS, to study the mice and the diseases they carried, specifically Lyme disease.

Historically, Lyme disease has been concentrated in the northeast and north-central U.S., but its range is expanding southward into Virginia and North Carolina. The first report of Lyme in eastern Virginia occurred in 1990, but there are now more cases reported in the mountainous parts of western Virginia and North Carolina. Brinkerhoff wanted to know why.

“One hypothesis was that black-legged ticks and the animals they infect have expanded their ranges southward along the Appalachian Mountains,” said Brinkerhoff. “A second hypothesis was that the Lyme disease bacterium was already present in this area, infecting a variety of animals such as the white-footed mouse, but not humans.”

To test the hypotheses, Brinkerhoff needed to look for the Lyme disease bacterium in white-footed mice that lived in Virginia and North Carolina before the rapid rise in the number of western cases.

“Lyme disease is caused by a bacterium transmitted by the black-legged tick, and one of that tick's most popular targets is the white-footed mouse,” Brinkerhoff said.

The museums supplied tiny pieces of the ears of 387 specimens collected before the year 2000. The oldest was from 1911. Brinkerhoff and his students tested the samples and found evidence of DNA from Lyme disease bacteria in mice that lived in eastern Virginia, but they found no trace of bacterial DNA from western mice. That supports the hypothesis that the western cases of Lyme disease are the result of the rapid southward range expansion of infected ticks and the animals they feed on.

A journal article on this research recently published in Ticks and Tick-borne Diseases.

“There are still questions here, including what’s causing the black-legged ticks to spread south,” said Brinkerhoff. “This study could be the beginning of other explorations as we could replicate this work with other mammal species currently housed in museum collections.”

# # #