The cumulative threat of diseases transmitted through tick and mosquito bites should be regarded seriously this summer and appropriate precautions taken, public health officials are warning.

Two sometimes-deadly forms of encephalitis, Powassan virus and West Nile virus, have been detected in Maine in the last few years. Three Mainers were most likely infected with Powassan by the bite of common woodchuck ticks in the last two years, while three birds found dead in Maine last year tested positive for West Nile virus. Birds can harbor West Nile, which may be transmitted to humans after the Culex species of mosquito bites the bird and later a human.

So far this year, neither virus has been detected in Maine, although officials expect to see West Nile again this year.

Even as these new, “exotic” illnesses grab the public’s attention, the chance of getting either is less than that of contracting Lyme disease through a deer tick bite. A record 100-plus Lyme cases were diagnosed in Maine last year.

The growing number of vector-borne diseases, those that travel with their carriers, may be a harbinger of others on the horizon.

“The real take-home message is it continues to show the evolution of infectious vector-borne disease,” said Dr. Kathleen Gensheimer, state epidemiologist. “We will undoubtedly see more.”

Gensheimer suggests that while the threat must be kept in perspective, all residents should take steps to minimize their risk of becoming infected.

Cleaning grounds around houses to minimize brush and tall grass reduces habitat for ticks. Getting rid of water that stands undisturbed for long periods of time in old tires, birdbaths or plugged gutters will reduce mosquito breeding.

It’s best to wear long pants and long-sleeve shirts when out at dusk or dawn – mosquito prime time. When walking through tall grass or brush, wearing light-colored clothing makes it easier to spot ticks. Insect repellent used according to directions can reduce insect bites.

Public health officials suggest using repellents containing DEET, which has some potential side effects, especially for children. The American Academy of Pediatrics recommends that repellents used on children should contain no more than 10 percent DEET. Adults should apply the repellent and avoid children’s faces and hands.

For adults, only repellents with 30 percent DEET or less should be used, public health officials say. For more detailed information on steps to reduce risk of infection, visit the Maine Bureau of Health’s West Nile virus page at http://www.state.me.us/dhs/boh/ddc/westnile.htm.

As the bureau continues to look for West Nile virus and other viruses, it has asked the public to report any suspicious, dead birds to its bird reporting hot line at 1-888-697-5846.

So far this year, the phone line has taken 397 calls. Through June 28, the state had collected 122 birds for testing. Of 37 complete tests, no birds were detected with West Nile, Gensheimer said Tuesday.

Last year the state collected more than 600 birds. Of those, three birds from South Berwick, Portland and Sabattus were determined to have West Nile.

Since the disease was detected for the first time in North America in 1999, it has spread from New York to 26 other states and the District of Columbia. Still, only 149 people have been diagnosed with West Nile since its North American appearance in 1999. Of those, 18 died.

Most people infected with West Nile will experience symptoms similar to a bad case of the flu. Those who are older or have weak immune systems risk getting severe brain swelling that can cause death. No vaccine for the virus exists. About 15 percent of those diagnosed with it die, according to the CDC.

Powassan encephalitis shares many of the symptoms of West Nile virus: muscle weakness, headache, fever, dizziness and sleepiness. Unlike West Nile virus, which is thought to be most dangerous to older people and to small children, Powassan is a significant threat to young and middle-age adults.

Although three cases have been found in Maine in 2000 and 2001, Powassan remains extremely rare with just a few dozen cases on record, mostly in Maritime Canada.

More common is Lyme disease, itself a relative newcomer discovered and named in 1977 in Lyme, Conn. Lyme disease symptoms often include fever, malaise, fatigue, headache, muscle aches, and joint aches.

On top of the more than 100 people diagnosed in Maine last year, many others received preventive antibiotic treatments without complete diagnoses after being bitten by ticks. Still other cases simply went unreported.