A generation ago, black flies and mosquitoes were the worst pests Mainers faced in the spring.

Today, blacklegged or deer ticks, which first arrived in the state in the 1980s, are present in most of Maine. Deer ticks carry Lyme disease, which can cause debilitating symptoms if not caught at an early stage, and babesiosis and anaplasmosis, which can cause flu-like symptoms and potentially be deadly to the very young, the very old or people with impaired immune systems.

Extremely rare, but of greater potential concern is the Powassan virus. Only about 60 cases of Powassan have been reported in the United States in the past decade but the number has been increasing. Powassan can cause serious neurological problems and about 10 percent of cases with serious symptoms have been fatal. There is no treatment for the disease.

For Mainers, particularly those who live in areas where tick populations are heaviest, the message is to focus on prevention and not to panic said Lincoln Medical Partners Internal Medicine Physician and Infectious Disease specialist Catherine Cavanaugh, DO.

“It is a different world than it was when we were kids,” said Dr. Cavanaugh, who is also a pediatrician. “People shouldn’t modify their enjoyment of the outdoors, but they do need to be far more vigilant than they ever have been.”

Because all of these diseases are spread by the deer tick, it is important that people be able to identify the deer tick and the symptoms of tick-borne diseases. Lyme disease, for example, has symptoms that largely mimic the flu. Victims often, but not always, have a slowly spreading pink rash where the tick was attached.

Because ticks need to be attached for 24 to 72 hours before they can transmit Lyme disease, it is also important that people do tick checks on a regular basis and remove ticks as quickly as they can, said Dr. Cavanaugh. Ticks tend to migrate to low traffic areas such as behind the knees, armpits, the groin area and the scalp.

If a rash is present around a tick bite or an engorged deer tick is removed, Dr. Cavanaugh said people should call their doctor immediately.

Developing good habits is particularly important on the Midcoast, where Lyme disease rates are among the highest in the country.

Maine had the highest rate of Lyme disease in the country in 2014 (the last year for which national statistics are available) with 87.9 cases per 100,000 people, according to the U.S. Centers for Disease Control and Prevention. That same year, Lincoln County had the second highest rate of Lyme in Maine with 242 cases per 100,000. The rate of Lyme disease dropped last year for only the second time in ten years, but remained at elevated levels throughout the Midcoast.

Anaplasmosis and babesiosis, two relatively new diseases that are also carried by the blacklegged or deer tick, are relatively rare but increasing. In 2015, Lincoln County had the highest rate of both diseases in the state, according to statistics from the Maine Centers for Disease Control.

Anaplasmosis and babesiosis aren’t likely to cause more than a fever for most, but for the very young or very old, or people with a compromised immune system, they can be very serious, even deadly. In Maine last year there were only 186 cases of anaplasmosis and 55 cases of babesiosis, compared to about 1,200 cases of Lyme.

Much more rare but of increasing concern is the Powassan virus, which caused the death in 2013 of Rockland-area based artist Lyn Snow.

Discovered in the 1950s, the Powassan virus was historically carried by ticks that rarely bit humans. Over the past decade or so, however, the virus has spread to the deer tick.

One reason the Powassan virus is a greater concern to physicians and biologists, is that it can be transmitted much more quickly – sometimes in less than an hour. A tick has to be attached for at least 24 hours before Lyme and other tick-borne diseases are transmitted.

Another reason for concern is that there is no treatment for the virus.

“The majority of what ticks carry we can treat and eradicate but there are some things we can’t,” said Dr. Cavanaugh.

Most people who are infected will experience few, if any, symptoms but in others the virus causes inflammation of the brain, resulting in long lasting neurological symptoms or death.

Charles Lubelczyk, a Vector ecologist at the Maine Medical Center Research Institute, said one critical question his team is trying to answer is how much of Maine’s tick population carries the virus.

Wildlife surveys indicate the virus is present at some level in most of the state. What isn’t clear is what percentage of ticks has the virus and can therefore spread the disease. For example, in parts of Maine about 60 percent of deer ticks have Lyme disease in the fall. That high rate of infection among ticks greatly increases the risk to humans

Lubelczyk said he is in the process of doing a state survey to determine how many ticks are infected with Powassan virus. That will give biologists an idea of the risk and it will also provide a benchmark to help determine if the virus is spreading.

The biologist said that when his team is in an area where the Powassan virus is present, they take strict precautions, wearing long-sleeve shirts, knee-high boots and tucking their pants into the boots. They also use permethrin (an insecticide that kills ticks) on their clothes.

After studying tick-borne diseases for more than a decade, Lubelczyk said one piece of advice he has for anybody in Maine is to do tick checks, and do them as promptly as possible.