Tick numbers are down in some areas, but experts warn against letting your guard down.
Despite headlines forecasting a bumper year for ticks, UNH Extension Entomologist Alan Eaton says the recent drought in New Hampshire caused tick populations to show only a slight increase. Speaking on NHPR’s The Exchange, Eaton says that in southeastern counties, such as Merrimack, Strafford, and Rockingham counties, there might even be slightly fewer ticks.
But New Hampshire still suffers from some of the highest tick densities in the nation: “We have 15 species of tick here…New Hampshire is tick-rich,” says Eaton. And the most common tick in New Hampshire is the black-legged tick, which Eaton says is “responsible probably for well over ninety percent of the tick-borne disease cases in our state.”
In May, both the adult and nymph black-legged ticks are active. “It’s important that we realize that the time of year when the risk of tick-borne disease is the greatest is right now, when the nymphs are active -- that’s because they’re so small they’re hard to see,” Eaton says. Nymphs begin emerging mid-May and are especially hard to see.
“New Hampshire has one of the highest rates of Lyme disease in the nation," N.H. State Epidemiologist, Dr. Benjamin Chan, says. "One thousand four hundred to sixteen-hundred people reported to the health department with Lyme disease, and this is probably an under-representation of the actual number of people that have this disease, because there are many people who may go undiagnosed or un-reported.“
A vaccine for Lyme disease was taken off the market in 2002 because it was poorly tolerated. Chan says, “to my knowledge there is not another vaccine that is at least close to coming out for Lyme disease…and I’m not aware of one on the horizon.”
There is, however, a new treatment being developed at the Mass Biologics Lab at UMass Medical School, called Lyme PRep, for Lyme pre-exposure prophylaxis. Dr. Mark Klempner says it's “a new but very old method for passive immunity” that uses a specific protein, or human monoclonal antibody, that is “perfectly able to prevent the transmission of the Lyme disease bacteria from the tick to the person.”
“Typically, antibodies only circulate for a month or so,” says Klempner. “What we’ve done is looked at antibodies that we can extend their half-life, so that they would circulate for six to seven months at a high-enough concentration, and then they would be gone during the time you don’t really need them. Then you’d get re-administered the following year.”
When will the Lyme PRep treatment be on the market? “We have made a lot of progress over the past year … we are talking to a number of larger pharmaceutical companies that we would need to partner with, in order to move it into the clinic,” says Klempner.
"We’re living in what we call a Lyme-endemic state, meaning Lyme is all around us,” says Chan. “And so we just need to focus more on preventing the tick bites, and ticks in general.”
Encouraging biodiversity is part of the fight against Lyme disease, according to disease ecologist Richard Ostfeld, of the Cary Institute for Ecosystem Studies. He makes the connection between plentiful acorns, mice, and ticks. “The oak trees that dominate many of our forests in the Northeast, including many parts of New Hampshire…every four or five years, they cut loose with a huge bumper crop of acorns…it’s almost like you’re walking on ball-bearings… Those acorns are very nutritious...wildlife love to eat them and to store them. And one of the key wildlife that does so is the white-footed mouse.”
The plentiful food allows the mice to “get a jump-start on their reproductive season, and so by the following summer the white-footed mice have reached a population peak," says Ostfeld.
The white-footed mice are ideal hosts for the larval stage of the black-legged tick, says Ostfeld, because they don't bother grooming. "So the ticks survive well, and they have a very high probability of getting infected if they bite a white-footed mouse. ”
The result: Due to the life-cycle of a tick, in the spring and early summer two years following a mast year of abundant acorns, the nymphs emerge with a high likelihood of being infected, not only with Lyme disease, but also with babeosis and anaplasmosis. “That’s when our risk goes up,” says Ostfeld. “The mice are the main source of infection for the baby ticks.”
Some hosts are good at grooming – for example, opossums kill about 95% of the larval-stage ticks that try to bite them. “We’ve estimated an individual opossum can kill up to several thousand larval ticks per week during the peak of the larval stage,” says Ostfeld.
Ostfeld blames forest fragmentation for the loss of habitat for other animals, such as fox and bobcat, that would prey on the white-footed mouse. Tick-borne diseases are such a public health problem that they “should inform the way in which the landscape is developed, so that we can preserve as large and undisturbed, unfragmented a patch of forest…as we can,” he says.
For areas already suburbanized, Ostfeld says, "we can pinpoint the riskiest areas, the places with the highest abundance of ticks, and target them for environmentally safe and effective means of controlling the tick population."
“Unfortunately, we’re not going to airdrop thousands of opossums, or bobcats, for that matter, into these areas, and hope they stick around," said Ostfeld.
As part of The Tick Project, Ostfeld is conducting experiments to control tick populations on a neighborhood scale, using MET52, a spray containing a fungus that occurs naturally in forest soils and has been shown to kill ticks. Eaton also recommends using MET52 on your property, as well as an insecticide called Essentria, which is a natural product made up of essential oils. “It works quite effectively and is a really viable option for people who really don’t want to spray a synthetic.”
DEET seems to be the most effective and durable personal repellent, but if you don’t want to use DEET, check the label for other active ingredients, including IR3535, Picaridin, and undecanone repellents. Permethrin is a synthetic repellent that “clings tenaciously to cotton and repels ticks,” Eaton says. It is sprayed directly on clothing and lasts through several washes. There are natural options, but Eaton says they are not as effective.
Prevention of tick bites is still the best weapon in our arsenal against tick-borne diseases. To hear the full conversation, click on this link. The Exchange webpage also features links to resources from UNH Extension, Alan Eaton, and the NH Department of Health and Human Services.