MONTPELIER, Vt. — Ticks that carry Lyme disease have reached into northern Maine and are increasing in Vermont, where the state’s entomologist expects cases of the disease to continue to rise and the insects to inhabit new areas.

Vermont, Maine and New Hampshire are among 17 states with high-risk counties for Lyme disease. The reasons for the increase in populations are varied: climatic factors, land development patterns and hosts like deer and rodents.

“Lyme disease is a real concern,” said Vermont state entomologist Alan Graham, who hopes to do a statewide survey of ticks this year.

New Hampshire had one of the one of the highest incidence rates of Lyme disease in the country, with an estimated 1,373 cases identified last year, according to the New Hampshire Department of Health and Human Services.

Symptoms of Lyme disease, which is transmitted by the deer tick – also called the black-legged tick – include a fever, headache and fatigue. Sometimes, there’s a rash that looks like a bull’s-eye on the tick bite. Most people recover with antibiotics, but if left untreated, the infection can cause arthritis and more severe problems.

Officials are urging residents to take precautions to protect themselves from bites from infected ticks, such as using insect repellent that is effective on ticks; avoiding overgrown grass, brush and leaf litter that may be tick-infested; wearing long pants and long sleeve shirts; and doing tick checks after being outdoors.

“We are coming upon one of the most active times for ticks in New Hampshire,” said Beth Daly, chief of the bureau of infectious disease control for DHHS.

Ticks also can transmit anaplasmosis, which causes fever, headache and muscle aches, and babesiosis, which is caused by a parasite. The rare virus, Powassan, which causes encephalitis, is also a concern.

In Maine, deer ticks first became a noticeable problem in the mid- to late-1980s in southern parts of the state. Now they’re found even in state’s northernmost reaches and are growing in western, central and eastern Maine.

Deer ticks are the most commonly encountered ticks by people in Maine, said Griffin Dill, coordinator of the tick ID program at the University of Maine cooperative extension.

AP reporter David Sharp contributed to this report from Portland, Maine.