A few months ago, the icy breath of the north that normally tucks itself over the Arctic during the winter blasted into the Northeast, prime tick country. This prompted climate scientists to look for links between a weakened polar vortex and a warming world. But those who study arachnids were interested in other signs … like fewer ticks.
In January, Thomas Mather, PhD, an entomologist known to many as the “tick guy,” trudged through thick snow in Kingston, R.I., looking for the spot where he’d buried vials of deer ticks the day before. The overnight temperature had fallen to a tick-numbing three degrees. Locating the vials, he sprinkled the tiny black specks on his palm. They sat there like pepper. Then they began to move.
For ticks, it seems, the ice age was a snowbird’s vacation. So don’t drop your guard, warns Mather, director of the University of Rhode Island’s Center for Vector-Borne Disease and its outreach arm, the TickEncounter Resource Center (TERC). Mather has spent two decades studying the rise of the blacklegged tick—commonly called the deer tick—in Rhode Island.
“I’m pretty certain that we won’t really be able to credit winter’s serial polar vortices for whatever the ticks are or are not doing in the spring,” he says. It’s not about the weather, but cycles. In their two-year lifespan, ticks feed on the blood of hosts during three growth stages: larval, nymphal and adult. According to Mather, the deer tick problems we’re facing in 2014 were largely decided last August and September by the number of larval ticks that found infected rodent hosts. “That will determine both the summer nymph populations and fall’s adult tick abundance,” Mather says.
In recent years, those cycles have produced record numbers of nymphs at the sites his team sample each summer. So many, in fact, that he considers it a public health crisis in his state, which is part of the East Coast “tick-belt.”
Mather says that human and pet encounters with ticks are skyrocketing, and while ticks don’t always carry a disease, they may, and many of those diseases are dangerous.
Between 2006 and 2010, Veterinary Week reported a 30 percent increase in the rate of dogs exposed to tick-transmitted diseases. Among them: The aggressive lone star tick can transmit ehrlichiosis, one of the most common and dangerous tick-borne diseases in dogs. The brown dog tick and American dog tick also spread ehrlichiosis, babesiosis and Rocky Mountain spotted fever (RMSF).
Then there’s the deer tick. Although there are hundreds of species of ticks—all of which are relatives of spiders and mites, in the U.S. —the deer tick is number one on the most unwanted list. It spreads several dangerous infections, Mather says, and topping that list is Lyme disease.
Trail of Infection
The deer tick in the East and the related western blacklegged tick are the only known transmitters of Lyme disease in the United States. The trail of infection typically begins with rodents or, in the West, lizards, natural reservoirs of the Lyme bacterium, Borrelia burgdorferi. Ticks need a blood meal to reproduce, and acquire the bacterium when they bite an infected host. The next time they bite, they inject the bacterium into their unlucky meal source.
Where Lyme is found, so are deer, but the “deer tick,” as it’s commonly called, is actually the blacklegged tick, and it feeds on many different mammals, birds and reptiles. This tick has been on a tear in the Northeast, its range expanding, its pathogens mutating, ever since the disease it spreads—long known in Europe—was recognized in 1975 in Lyme, Conn.
Lyme disease was first diagnosed in a dog about 25 years ago, and now it’s one of the most common tick-borne diseases in dogs in the U.S., notes Cornell University’s Baker Institute for Animal Health. In several of the most affected states, one out of 15 dogs tested positive for Lyme disease in 2011, according to a study by the Centers for Disease Control and Prevention (CDC). And where dogs test positive, so do humans. In 2012, 95 percent of human cases were reported from 13 states concentrated in the Northeast and upper Midwest.