Though New Hampshire’s Department of Health and Human Services is not likely to go to the extremes of culling the state’s deer population in an effort to reduce blacklegged ticks (formerly known as deer ticks) in order to put a stop to the increasing cases of Lyme disease in humans, it is looking at some other creative options — and they will likely require residents to help.
The Division of Public Health at DHHS recently released a Tickborne Disease Prevention Plan and says the plan is a living document it hopes to constantly update with new information.
The bacterial agent that causes Lyme disease, the spiral-shaped Borrelia burgdorferi, is transmitted to humans only through blacklegged ticks after they’ve had their first meal, usually from an infected white-footed mouse.
“We have a serious problem with Lyme disease in our state,” said Abigail Mathewson, the state public health veterinarian. “For the past several years, we have been ranked in the top five for the incidences of Lyme disease. We don’t expect that to change any time soon.”
She said that in 2013, the state had 1,691 cases of Lyme disease. In 2004, there were only 192 reported cases. While the jump in reported cases can be partially attributable to medical providers improving their diagnostic abilities, the tick population is also climbing.
The state’s prevention plan is full of ideas on how to tackle the problem by dealing with the hosts themselves, which requires an understanding of how different hosts play important roles, both in the transmission of the disease and in the tick’s lifecycle.
“When you think about the tick lifecycle, it requires a first host for the larva, and then a second host for the nymph and a third hose for the adult,” Mathewson said. “Generally the first host is something small, like rodents, small mammals, birds, things like that.”
And it’s the nymph stage — which, if you remember your high school science, is sort of the adolescent stage for some bugs — that has the state most worried. Nymphs are out looking for a meal during late spring through most of summer, and that’s when Lyme disease cases spike.
Mathewson said adult ticks can transmit it too, but they are less likely to because they’re bigger and easier to catch, and it takes longer for them to transmit the bacteria.
The first hosts, usually small critters like the white-footed mouse, are called reservoir hosts, Mathewson said. They carry the bacteria in their blood and it doesn’t make them sick. The adults like to hitch a ride on deer in order to mate and grab a meal before dropping off and laying eggs. So the deer are called reproductive hosts.
One option some places have experimented with to prevent Lyme disease is eliminating deer entirely.
“If we did complete elimination of deer, we would not be able to sustain that in New Hampshire because we’re not an island,” Mathewson said. “We would have deer coming in from all our borders.”
Plus, she said, deer are pretty, we like to have them around and getting rid of them could have undesirable effects on the ecosystem. And it could backfire.
“Those adult ticks are going to be looking for another host, so they may be more aggressively attaching to humans because the deer are gone,” Matthewson said.
The state also weighed using contraception in the deer population but decided it would be too difficult.
Finally, the state also looked at ways to control the reservoir hosts.
Eliminating white-footed mouse cannot be done on a massive scale, but landowners and homeowners can set poison bait for the mice. This can be effective, but it might cause other unforeseen problems.
“There’s some concern now with [the poison] moving up the food chain,” Mathewson said.
Exclusion from buildings is ideal, she said. Part of that is not only keeping mice out, but moving your birdfeeder away from the home in the spring and summer since ticks can fall off birds like robins and thrushes and land close by. Also, if property owners have rock walls, she recommends blocking any holes that can be used for mice to nest in.
One of the more interesting options that may soon be available to the state is vaccination of white-footed mice. An effective vaccine has been developed, but the trick is delivering it.
“The studies seem like it’s a promising modality, but it may be logistically unfeasible,” Mathewson said. “It would be very interesting to find out if they do larger studies of it to [figure out] the feasibility of it; how expensive would it be, how long you have to do it, how often you have to maintain the bait boxes during the season. Things like that.”
Bringing the fight to the ticks
DHHS attributes the recent growth in tick numbers to things such as the state’s reforestation after no longer being used for heavy logging and agriculture compared to 200 years ago. New Hampshire is now the second most forested state, with an estimated 84 percent forest cover. That creates habitat for some of the ticks’ preferred hosts like deer.
Meanwhile, invasive species of plants like Japanese barberry have been shown by scientists to provide ticks with an ideal micro-climate for them to thrive in.
And UNH entomologist Alan Eaton said other than some fungi, ticks don’t have many natural enemies.
“Not too many [predators] that we know of,” Eaton said. “I’m sorry to have to say that.”
In 1991, the average number blacklegged ticks found on harvested deer at a check station was .03. As of 2013, that number has gone up to 5.67. And in Rockingham, Merrimack and Carroll Counties, 100 percent of deer harvested there in 2013 had ticks.
Eaton has counted more than 700 blacklegged ticks in his studies over the past 25 years, and he says the number is higher every year.
“[The population] continues to go up and up and up,” said Eaton.
He suggests a few ways to attack the ticks themselves. Some range from bait boxes that treat mice with fipronil, the same stuff we put on our pets to protect them from ticks, to strategically planting pesticide-treated cotton around a property to be gathered up by mice who line their nests with it. But one of the simplest things you can do, according to Eaton, is mow your lawn.
“Instead of having knee-high grass, have grass that’s 3 inches high,” Eaton said. “Things like this make it much, much harder for ticks to survive a long time.”
The reason for that, he said, is they dry out faster when exposed to more sunlight.
In fact, the number one killer of ticks is dry heat, so the drought New Hampshire was experiencing in early and mid May has a silver lining, Eaton said.
“We had some tick activity early [this spring] but then it got drier and drier and drier. As it gets drier, the ticks stop their questing activity, which means searching for hosts,” Eaton said. “They burrow down … into the soil to hydrate again.”
As seen in the May 28, 2015 issue of the Hippo.