The northeast US faces potentially "the worst year yet" for Lyme disease and other tick-borne infections because of the periodic abundance of a little noticed component of the disease's complex ecology: acorns.
Dr. Richard S. Ostfeld of the Carry Institute of Ecosystem Studies in Millbrook, New York explained during a recent presentation at the International Conference on Emerging Infectious Diseases (ICEID) that a heavy crop of acorns in 2010, a phenomenon known as a "mast year" fueled a 2011 population bloom in white-footed mice, which stash acorns for winter food and begin breeding earlier in years when they are well fed. That surge intersected with the two-year life cycle of the ticks that transmit Lyme disease, for which mice are the key host, and this summer could produce a bumper crop of infected tick nymphs looking to bite large mammals - including humans.
The health departments in Lyme endemic areas are already crafting messages to the public about the potential health risk.
The prediction relies on the key role that white-footed mice play in perpetuating Lyme disease. That species, appears to be the most competent reservoir for Borrelia burgdorferi, the bacterial cause of Lyme. Mice sustain the infection without cost to themselves, are frequently bitten by tick larvae and groom off or otherwise kill the larvae at lesser rates than other small mammals that are bitten - allowing the larvae to drop off naturally and complete their transformation into tick nymphs that transmit infection in their second year of life. Mice also can survive in much smaller areas than the larger animals, chiefly deer, that are usually blamed for perpetuating Lyme. In a sampling of "forest fragments" sliced up by development in three northeastern states, which include New York State, a parcel as not been found in which mice did not thrive.
Because of the yearlong gaps between bumper crops of acorns, mice and then ticks, the reliable but irregular masting phenomenon could be used as an early warning signal for Lyme exposure risks. Oak trees mast roughly every three to five years, "and when you are in a mast year, you always know it."
Dr. Ostfeld says he and others are working with health departments throughout the state to warn the public in areas where Lyme disease may be an issue.
As always, if you or anyone knows someone that has Lyme disease and needs financial help please give me or any board member a call.
Column Posted on Web Site April 22, 2012
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