Ticks on the March

Horse owners should be on the lookout for Lyme-disease-carrying ticks earlier in the spring
Horse owners should be on the lookout for Lyme-disease-carrying ticks earlier in the spring. | © Dusty Perin

May is Lyme Disease Awareness Month in the United States and Canada, but officials may want to switch the date to April if current trends continue. Blacklegged ticks, which spread this disease, are emerging earlier in spring and showing up in new geographic areas, research data shows. That’s bad news for all critters affected by Lyme, including horses and people. 

The news comes from scientists at the Cary Institute of Ecosystem Studies, an independent, not-for-profit research center in Millbrook, New York, who have been studying blacklegged ticks and gathering information about tick-borne disease risks for
nearly two decades. Blacklegged ticks can spread several diseases, including equine granulocytic anaplasmosis (ehrlichiosis), sometimes in the same bite, but Lyme disease
is the most common tick-borne infection in the United States. 

The ticks go through three life stages—larva, nymph and adult—and need a blood meal before molting from one stage to the next. They pick up the bacteria that cause Lyme disease (Borrelia burgdorferi) as larvae and nymphs by feeding on infected mice, and they pass the bacteria on to their next victim—horse, human, dog, deer or some other mammal or bird. Cary Institute ecologist Richard S. Ostfeld, PhD, and his team report that climate warming trends correlate with earlier spring feeding, sometimes by as much as three weeks. 

“People need to be tick-vigilant before May, as potentially infected nymphal ticks are searching for their blood meals earlier and earlier,” Dr. Ostfeld states. Warm temperatures also allow the ticks to stay active longer in fall. Cold weather stops the activity, but they can overwinter in leaf litter and come out again in the first warm days of spring,

Blacklegged ticks are concentrated in the Northeast and the Great Lakes regions but also occur in pockets in other areas, including the South and on the West Coast. (The eastern ticks are commonly known as deer ticks; those on the West Coast are Pacific blacklegged ticks.) Not surprisingly, Lyme disease is also heavily concentrated in these regions. However, the ticks have been steadily spreading north and west, expanding their range. For example, recently deer ticks turned up in several parts of North Dakota, and some carried the bacteria that cause Lyme and other diseases.

Climate change partly accounts for the ticks’ expanding range, the scientists say, but there are other factors at work. Ticks travel by hitching rides on host animals like deer, so increased numbers of those animals are a factor. And in many areas former farmland has reverted to forest or been carved into suburban yards, providing the sort of shrubby habitat that ticks and their host animals like.

Tick bites don’t always lead to disease, even if the tick is carrying the infection. But Lyme disease is as serious for horses as it is for people, with long-term complications that can include chronic lameness and damage to the horse’s nervous system, heart and vision. If you live in a high-risk area, be on the lookout for the ticks that spread it.

This article originally appeared in the May 2015 issue of Practical Horseman.

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