PORTLAND – Increased surveillance for West Nile infection in mosquitoes, birds and humans will help public health officials determine how much of a threat the disease poses to Maine.

The results of the state’s surveillance program will help officials decide on next year’s strategies, including the possible use of pesticides to control mosquitoes. Dr. Dora Anne Mills, director of the Maine Bureau of Health, said that whatever the results, the focus this year and next will be on educating the public on personal protective measures.

The virus can cause serious illness and even death. But the chances of a healthy person becoming ill after being bitten by an infected mosquito are small.

“West Nile virus is a drop in the bucket compared to the enormous amount of death and disability that heart disease and lung disease cause in Maine,” Mills said.

The West Nile virus has been discovered in four dead birds – found in Portland, South Berwick, Sabattus and New Vineyard. The discovery has prompted stepped up efforts to test mosquitoes.

Since 1999, when the West Nile virus was discovered in New York, health officials and others have been tracking the progress of the disease toward Maine.

Last summer, the West Nile Virus Work Group asked the public to report any dead birds so they could be tested for the virus. That effort led to the discovery last week of the four infected birds – a sharp-shinned hawk, two crows and a blue jay.

Public health officials in the Portland area plan to begin a public education campaign next spring.

“It’s something we ought to watch,” said Nate Nickerson, director of Portland’s Public Health Division, “but I don’t think in any way we ought to treat it as if it’s an epidemic or there’s some tremendous health risk at this point.”

The state’s surveillance program includes the trapping and collecting of adult female mosquitoes. Researchers set traps in various locations – including Wells, Kittery, Berwick, Sanford, Portland and Augusta.

“After you do this bird surveillance, then the second step is to enhance mosquito trapping in those areas to see whether or not what you’ve got represents a true ecological invasion in those areas, or whether it’s a migrating bird that just came from some other infested area and died,” said Dr. Kathleen Gensheimer, the state epidemiologist.

Mary Holman, a research associate at the Maine Medical Center Research Institute, is one of those participating in the mosquito surveillance. She uses a trap of both light and dry ice, which gives off carbon dioxide to attract mosquitoes. She ships each “mosquito pool” – a batch of specimens belonging to the same species – to the public health laboratory in Augusta, where they are tested for the West Nile virus.

In some states, up to 50 percent of a mosquito pool has tested positive for West Nile. So far, Maine has had no positive pools, but three have been found in New Hampshire near the Maine border.