Are Deer to Blame for the Spread of Lyme Disease?

Are Deer to Blame for the Spread of Lyme Disease?

Public health officials in areas plagued by Lyme disease long assumed that because the black-legged “deer” tick is the main vector involved in its spread, lowering whitetail density would lower the risk of human infection. But recent research casts doubt on the benefits of drastically cutting deer numbers. A more effective way to fight Lyme disease, it appears, is to increase the number of small-mammal predators, especially foxes.

A study by researchers in the Netherlands suggests that where fox numbers remain high, mice, voles, chipmunks and shrews that host Lyme-infected ticks are less active outside their burrows and aren’t as likely to pick up ticks carrying the bacterial disease. That translates to less Lyme transmission.

Foxes are the primary native predators of these small mammals. However, in eastern North America the overall number of foxes has dropped in recent decades, due to a huge increase in coyotes. Where coyotes are abundant, foxes aren’t. While coyotes eat some small mammals, they’re far less efficient at limiting their activity.

Named for Old Lyme, Connecticut, the site of its discovery in 1981, Lyme disease is caused by the bacterium Borrelia burdorferi. Many deer hunters have contracted it from ticks. Common symptoms include fever, headache, fatigue and a skin rash called erythema migrans. If untreated, Lyme can spread to joints, the heart and the nervous system. In extreme cases, death from heart failure has been documented.

According to the Centers for Disease Control and Prevention, around 95 percent of Lyme cases in humans are from one of 14 states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia and Wisconsin. (Note, however, that case locations reflect victims’ residences, not necessarily locations in which the disease was contracted.)

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