Few Mice Sets Stage For Highly Active Tick Season

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By: Michael C. Bailey
Published: 03/30/12

 It is tick time on Cape Cod.

Across the region, as people took advantage of the recent run of unseasonably warm weather, Cape Codders found themselves already pulling the little bloodsuckers off their pets and themselves—and, according to Larry Dapsis, entomologist and deer tick project coordinator with the Cape Cod Cooperative Extension, that trend is going to continue throughout the year in a big way.

“There is going to be an increased opportunity to encounter ticks this year,” Mr. Dapsis said, though he was careful to clarify that this would not be due to an increase in the tick population.

In fact, based on historical data collected by his predecessor, the late David Simser, Mr. Dapsis said 2012 is going to be a down year for the tick population, which has a two-year life cycle. “During odd-numbered years, the population is higher than in even-numbered years,” he said, though this is a quirk of timing and not driven by any specific factor such as the weather.

However, the weather is playing a role in the increased opportunity for the encounters Mr. Dapsis mentioned. “There is going to be a higher risk of encountering ticks and contracting a tick-borne disease,” he said, “but it’s not going to be because of the mild winter.”

The stage was actually set last spring, which was abnormally wet and led to a virtually non-existent crop of acorns in the fall of 2011. The dearth of acorns meant that the mouse population, particularly among white-footed mice, “has crashed,” Mr. Dapsis said.

Without those mice, the ecosystem loses a very important source of natural pest control. “Mice play the role of minesweeper” in that they pick up the bulk of the deer tick nymphs that typically emerge in May, he said, “and every tick they intercept is one less tick for humans to encounter.”

Mr. Dapsis said the relatively mild winter temperatures are noteworthy only because it has led to ticks becoming more active earlier in the year than normal, and when combined with the decrease in the mouse population, “it means they’re out for a longer time and have fewer choices.”

Cold Not A Factor

“Tick season starts in January and ends in December,” he said, dispelling the myth that cold kills ticks outright. They are in fact “incredibly adaptive organisms” that are highly resistant to the cold and can remain active throughout the winter months; their activity is only suppressed by frigid temperatures. “Winter is a low-activity zone.”

“When it gets above freezing, the adult ticks start moving and start looking for a meal,” Mr. Dapsis said, although he said this year’s mild temperatures meant the tick population was more active than normal. “I’ve been getting calls from people all winter long saying they’ve found ticks on them.”

He further noted that winter is when deer ticks are more likely to be carrying Lyme disease. “On average, about 25 percent of nymph deer ticks we find carry Lyme disease,” he said, “and in the adults we find in the fall and winter, about half of them have it.”

The nymph stage, which typically occurs between May and July, is still the period when deer ticks are most likely to pass on the bacteria that cause Lyme disease, and this year that risk is even greater due to the blow to the mouse population.

Mr. Dapsis said he reviewed historical data and found that in 2004, the acorn crop plummeted following a wet spring, and in 2005, according to the Massachusetts Department of Public Health, “we had a 47 percent increase in Lyme disease incidents in Massachusetts.”

Nymph deer ticks are extremely small—about the size of a poppy seed—and may easily go undetected even after they attach to a host. A deer tick must be attached for at least 24 hours for the disease to transmit to its host.

Symptoms of early Lyme disease may appear in as little as three days or as long as 30 days after infection, and may at first seem like symptoms of the flu: fever, headache, stiff neck, sore and aching muscles and joints, fatigue, and swollen glands.

Sometimes the area where the tick attached manifests a small red rash that develops a ring-like appearance.

A regimen of antibiotics during the early stages can prevent more serious effects later on. If left untreated, late-stage Lyme disease symptoms may occur, including chronic arthritis in the joints, and nervous system issues such as meningitis, weakness of facial muscles, and pain in the extremities. These symptoms may take years to manifest.

The US Centers for Disease Control and Prevention reported that in 2010, the last year for which full data were available, 94 percent of all reported Lyme disease cases came from 12 states, including Massachusetts. The state recorded 2,380 confirmed cases in 2010, ranking fifth in the nation, and 883 probable cases.

While Lyme disease has been receiving increased exposure in the public health community, Mr. Dapsis said there are two other tick-borne diseases that are still flying under the radar: babesiosis, a malaria-like illness, and anaplasmosis, which infects white blood cells.

Mr. Dapsis said deer ticks can carry one or both bacteria along with the Lyme disease bacterium, and tests conducted on ticks sampled last summer on Cape Cod showed that 10 percent of deer tick nymphs carried one other bacterium along with the Lyme disease bacterium. “It’s not just about Lyme disease anymore.”

The Cape and islands region accounted for half of all babesiosis cases reported last year in Massachusetts, he added.

Protection Against Ticks

“Our mantra is: protect yourself, protect your yard, protect your pet,” Mr. Dapsis said, and for self-protection, he recommended items containing the chemical permethrin. “It’s the one item that is not talked about enough, but it is the most effective.”

The low-toxicity insecticide, which is used in scabies medication for infants, can be applied to clothing to repel ticks. Mr. Dapsis said he treats his clothing with it before heading out into the field, “and after about 30 or 40 seconds of contact, any ticks on me will drop off…10 minutes later, they die.”

He has heard of people who spray the chemical on bandanas that they tie around their pet’s neck, a measure they use instead of or in addition to more conventional tick treatments.

As for yards, Mr. Dapsis said most residents have nothing to worry about. “Ticks aren’t a problem in the middle of the yard, but rather at the treeline,” he said, explaining that deer ticks prefer the shadier conditions of the woods to open grassy areas, which is where people are more likely to encounter the deer tick’s larger cousin, the brown tick (also known as the dog tick).

For more information about deer ticks and Lyme disease, visit the Cape Cod Cooperative Extension’s website or the official website of the nonprofit Lyme Awareness of Cape Cod at www.lymeticks.org.

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