To curb the spread of Lyme disease in the northeastern United States, scientists and public health experts for decades have targeted white-footed mice as the prime hosts for the immature ticks that ultimately drive transmission to humans.
This strategy has had only limited success.
Using a research technique on ticks called bloodmeal identification, scientists at Cummings School of Veterinary Medicine at Tufts University have now uncovered why they believe these efforts have fallen short.
It turns out that, at least on Martha’s Vineyard, it is the shrews who harbor the most disease-bearing young ticks, says Heidi Goethert, Sc.D., J93, research assistant professor at Cummings School. She is the first author of a recent study published in The American Journal of Tropical Medicine and Hygiene describing the researchers’ technique and findings.
On Martha’s Vineyard, shrews were the most common host for ticks, with mice and shrews contributing equally to the population of infected nymphs. On Nantucket, mice and deer were the most common host for nymphal ticks, but it was mice and shrews that are responsible for the most infected ticks.
“An important part of the study is the fact that minor hosts that don’t feed a large percentage of the overall number of ticks in a location can have a disproportionate responsibility for the number of infected ticks they contribute,” says Goethert.
Martha’s Vineyard and Nantucket have among the highest levels of tick-borne diseases in the U.S.
“We suspect that different small mammals harbor larval and nymph ticks in different areas of the country where Lyme disease is prevalent,” Goethert says. The team believes using their enhanced technique to identify and target the correct range of hosts, rather than focusing solely on mice, could make combating Lyme and other tick-borne diseases more effective in the future, not only on the Vineyard and Nantucket, but across the Northeast.
Prior research had focused on trapping studies to identify hosts that infect larval and nymphal ticks with Lyme disease. It turns out that mice are easier to trap, but shrews, moles, squirrels, chipmunks and other possible carriers are harder to trap.
In this study, Tufts researchers collected ticks by “flagging.” A fluffy white cloth is dragged over leaves and other vegetation where nymphal ticks hide. The ticks latch onto the cloth. Using their new technique of bloodmeal identification, they are able to detect small bits of DNA left over from blood the ticks consumed as larvae nearly a year earlier. In this way, researchers can identify which animal hosted them at the beginning of their lifecycle.
The scientists in this study limited collections to a single site on each island, as bloodmeal analysis can be affected by small variations in the vegetation the ticks are found on. “The new technique has an 80% success rate in identifying what host the tick fed on. Prior work in this area over a 20-year period had a 30%–40% success rate,” Goethert says.
Wide range of interventions needed
“We had thought for a long time that the mice were the prime host for larval ticks, that they were the end-all-and-be-all for breaking the cycle,” says Goethert.
Mouse-bait boxes, insecticides focused on mice, and other techniques have been used extensively for years against tick-infested mice, together with deer treatment bait stations that kill adult ticks on deer. Efforts to thin deer herds through expanded hunting is another method that has been tried to slow the spread of Lyme disease but has been controversial.
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“Unfortunately, mouse-targeted interventions don’t work on shrews and other hosts,” says Goethert.
“What our research shows is that we need to start creating interventions that address a wider variety of hosts,” she says. “This work also needs to be replicated on mainland sites, so we can identify which small mammals are carrying the most ticks and target those animals.”
Goethert notes that tick hosts will also change from year to year as rodent populations have boom and bust cycles. “The mice population on Nantucket, for example, experienced an extreme downturn for unknown reasons, and chipmunk populations are up and down on the Vineyard,” Goethert said.
While small mammals become infected with Lyme disease, they do not develop symptoms. Researchers hypothesize that developing a better understanding of how the immune response works in natural hosts might lead to the development of a possible vaccine.
In the meantime, the best way to avoid getting Lyme disease remains avoiding getting bitten by a tick by performing regular tick checks, wearing clothing (preferably permethrin-treated) that covers exposed skin and using insect repellant with DEET.
More information:
Heidi Goethert et al, Minor Hosts Have a Major Impact on the Enzootic Transmission of Borrelia burgdorferi, The American Journal of Tropical Medicine and Hygiene (2024). DOI: 10.4269/ajtmh.24-0283
Citation:
Shrews identified as big driver of Lyme disease in Martha’s Vineyard, Nantucket (2025, March 12)
