Summer is a great time to be roaming the fields and woods of Maine. Before venturing out though, it’s wise to take extra precaution against tick bites by tucking pant legs into socks or applying repellent. Deer ticks, correctly known to entomologists as black-legged ticks, Ixodes scapularis, carry the bacteria that cause Lyme disease. Lyme disease has apparently come to the coast of Maine to stay, and it is spreading steadily into central and eastern Maine.
Researchers at the Maine Medical Center’s Vector-borne Disease Lab track the progress of Lyme disease across the state by collecting and analyzing ticks. “We get 100 deer ticks off a single deer at a tagging station on opening day of hunting season,” says Chuck Lubelczyk, field biologist for the Vector-borne Disease Lab. “Each tick, if you dropped it in the woods, could lay 3000 eggs apiece. So from one deer alone you could have 300,000 ticks next season.” Small wonder the disease is spreading!
Lyme disease was first discovered in the United States near Lyme, Connecticut, in the mid 1970s. It is caused by the microscopic bacteria Borrelia burgdorferi, a corkscrew-shaped microorganism. Ticks pick up the bacteria by feeding on hosts such as birds, mice, rats, chipmunks and other rodents. White-footed mice are major carriers of the Lyme bacteria, though they do not contract the disease. Typical symptoms include fever, headache, fatigue and skin rash. Untreated, the disease can lead to joint stiffness, achiness, and ultimately will attack the heart nervous system. The number of Lyme disease cases has increased rapidly since its discovery, to the point where it is now the most common vector-borne (transmitted by insects or ticks) disease in the United States.
Most people contract Lyme disease in late spring and summer when ticks are in their tiny nymph stage and most active, and when people are outdoors most. Though adult ticks often feed on deer, the deer are not infected. But as Lubelczyk points out, they are very effective at transporting ticks and maintaining tick populations.
Deer And Lyme Disease
Hunters and wardens aren’t the only people paying attention to Maine’s deer herd. Lubelczyk, Peter Rand and Eleanor Lacombe at the Vector-borne Disease Lab are vigilant not only about deer numbers but of the ticks on their hides, too.
Managing Maine’s deer herd used to be a lot simpler. State biologists could gather data from the annual harvest across the state, come up with an estimate of herd sizes, jiggle the numbers based on how hard last winter was and come up with a target for next year’s hunt. Hunters in turn could be counted on to reliably harvest about that number. A gross oversimplification to be sure, but life has become increasingly complicated for deer managers at the Maine Department of Inland Fisheries and Wildlife (IFW) since Lyme disease arrived. Every 10 or 15 years when wildlife biologists review the state’s deer management plan they come up against the reality that Lyme disease is spreading farther and farther across the state.
With white-tailed deer acting as a prime host for disease-carrying ticks, biologists now have to look at deer management in a much broader context than for hunters wanting to Bag The Big Buck.
“In the past, our goal was to increase deer numbers” in most wildlife management districts, notes Lee Kantar, state deer biologist with IFW. Things changed in 1999 when IFW’s 2000-2015 deer management plan was developed. “[The plan] calls specifically for dropping deer numbers in southern and central districts of the state, now,” says Kantar.
It’s a big change, Kantar says, because it strikes a balances between the benefits of abundant deer — good hunting and wildlife viewing — with the negative impacts of over-browsing and Lyme disease. “It’s impressive because white-tailed deer are singled out for positive and negative impacts,” says Kantar. “Our job is to balance the extremes. It’s good to recognize that the potential risk of Lyme disease is written in the goal for deer management. In southern and central Maine (roughly below a line from Bethel to Dover-Foxcroft to Mt. Desert) the state manages deer densities for risk of Lyme.”
Managing deer is the way to manage ticks. One need only look to the case of Monhegan Island to dispel any doubt. Monhegan was infested with deer ticks in the 1990s. At that time the deer herd had grown to beyond-flourishing: deer were everywhere, including in peoples’ gardens. Scarcely any island vegetation was spared their voracious browsing. The problem got to the point where, by the mid 1990s, 13 percent of Monhegan residents had contracted Lyme disease. The community decided to remove deer from the island completely. That may have rankled some animal lovers, but the decision essentially was one of restoration: deer had been introduced to the island in the 1950s, and hunting and predation were not enough to control the population. With deer numbers averaging 50 per square mile, controlling Lyme disease was a vital concern.
Over three winters, all of Monhegan’s deer were removed. What followed was an initial surge in Lyme-infected deer ticks, followed by a precipitous drop. Within three years, Dr. Rand, Lubelczyk and the Vector-borne Disease Lab team reported that Lyme-infected adult ticks were virtually eradicated. “Without deer to feed on, the ticks stopped reproducing,” says Lubelczyk. “They won’t rebound. In order to complete their life cycle, they need deer. Without that final meal they can’t lay eggs; they’re not sterile, but they don’t reproduce. By contrast, on most of the Maine coast deer numbers are high enough to support high tick numbers.”
Monhegan’s case may seem extreme but in fact it was not uncommon for islands and southern and Midcoast towns to have 50 deer per square mile. IFW’s Kantar says that if deer numbers are kept within 15 to 18 deer per square mile, the risk of Lyme disease is lower. From 1999 to 2007, wildlife management district 24 (the Maine coast from Kittery to Phippsburg) had 50 per square mile. This past winter, Deer density in zone 24 dropped from 50 to 16.6 deer/sq. mi. because IFW started considering Lyme disease in its management of the herd (vs “more deer is better hunting”). And at 16.6/sq mi, Lyme is much less a threat.
Lubelczyk says plenty of Maine islands have deer and white-footed mice, and that means Lyme disease could be just around the corner. Just back from a field trip to Cape Elizabeth, Lubelczyk reported finding mice and chipmunks coated with 30-40 ticks each. “In the fall, 60 percent of the adult ticks on southern Maine coast are infected” with the Lyme spirochete, says Lubelczyk.
Maine Medical Center’s Vector Borne Disease Lab has a free tick identification program. Ticks picked off people and animals over the years and sent in to the lab have charted the steady advance of Lyme disease into the state. Lubelczyk advises people who find an attached tick to carefully remove it, and store it in a pill container in alcohol. If you can tell the difference between a deer tick and a dog tick, they prefer to receive just the deer ticks. Ticks received from any islands are especially of interest.
Mail ticks to: Maine Medical Center, Vector-borne Disease Lab, 75 John Roberts Road #9b, South Portland, ME 04106.