Scientists recently discovered a new virus carried by the tiny bloodsuckers.
They aren't yet sure if or how it will affect human health, but the potential for severe illness is there, according to the April-June issue of the Center for Disease Control's journal Emerging Infectious Diseases.
Seven other illnesses have been linked to ticks, which wait on the ends of grasses and shrubs to latch onto passing people and animals.
Now, researchers at Harvard University, Yale University and in Spain have isolated a new virus in deer ticks in New England. While they aren't sure how it will affect human health, related viruses discovered in Europe cause severe brain swelling and can be deadly.
"If it does affect humans here, the potential for severe illness is there," said Sam Telford, a parasitologist at the Harvard School of Public Health.
Telford and a team of scientists discovered the virus while studying bacteria that cause human granulocytic ehrlichiosis, a potentially fatal illness identified last year that is caused by black-legged ticks.
The team was studying the salivary glands of ticks when it came across the virus. When the team injected the virus into mice to study its effects, the mice died quickly.
"Just the fact that deer ticks have a virus is cause for concern," Telford said.
People "need to be that much more vigilant," said Dr. Andre Weltman, Pennsylvania public health physician.
Lyme disease remains the most common tick-borne disease. Reported cases of the disease are on the increase in Pennsylvania, as well as in Maryland and West Virginia, said public health officials from each state.
Some, but not all, of the increase is due to better awareness about the disease, which can be difficult to diagnose because its flulike symptoms mimic other problems.
Only a handful of Lyme disease cases are reported each year in the seven-county Tri-State area, they said.
Alex Prouty, who teaches archery at Mount Aetna Camp, said he doesn't let ticks bother him.
"My chances are much greater at getting hit by a drunk driver than getting some spooky disease from some insect bite," said Prouty, 23.
The good news is that this tick season appears to be milder than in years past, possibly because of the dry weather. Snowy winters and rainy springs provide conditions in which ticks thrive.
Area camp counselors said they have seen fewer ticks.
Still, David Hykes, manager of Camp Penn north of Waynesboro, Pa., found one crawling up his sock in early June.
People can expect to continue coming into contact with ticks, especially as people build houses in their habitat, Weltman said.
"People really need to be cautious, on the lookout for ticks, especially when they've been out in the countryside," said Dr. John Newby at Washington County Hospital.
It takes at least two days for Lyme disease to be transmitted from a tick bite.
After three days, the circular bull's-eye rash may appear.
Other symptoms include fever, headache, tiredness, stiff neck, joint pain and swollen lymph nodes.
Weeks, months or even years later, the disease can cause arthritis, or nervous system disorders like numbness, pain and meningitis.
There are more than 850 species of ticks worldwide, 100 of which transmit diseases.