Mosquitoes: Beware the bite

By Thomas L. Treadwell, M.D.

Public health officials tracking infectious diseases are on heightened alert this year, as an extraordinarily wet spring and summer have led to an explosion in the mosquito population. With such a boost some reports indicate we have twice the number of mosquitoes over last year fears of diseases like West Nile virus and Eastern Equine Encephalitis (EEE) are growing. With some months to go before the first hard frost ends the threat, it's prudent to remind ourselves about these illnesses and the preventive steps we can take against them.

Through the first week of August, no human case of either illness had been recorded and no trace of EEE had been found in the state this year. But the Massachusetts Department of Public Health (DPH) has identified at least 10 communities where West Nile virus (WNV) has been found.

Here's some background on both illnesses, and what you can do to avoid them.

EEE and WNV are viruses, and both exist in nature in a cycle that involves birds and mosquitoes. Birds carry the virus; mosquitoes bite the bird, and so forth. The possibility of human infection increases typically in late summer, after "amplification" of the cycle that is, when more birds get infected. So while human cases are rare for both viruses, they tend to occur in late summer.

Both EEE and WNV are spread through the bite of an infected mosquito, although WNV can also be passed through blood transfusion or organ transplants. People do not become infected with either disease through contact with other infected people, birds, or animals. Most important, no treatment exists for either EEE or WNV. (A vaccine is available to protect horses from EEE.)

According to the Centers for Disease Control, Massachusetts has the fourth highest number of EEE cases. However, the disease is extremely rare, and fewer than 100 cases have been recorded in the last 70 years. But EEE presents a greater danger than WNV.

About half the people in Massachusetts who have contracted EEE have died, and people who survive will often become permanently disabled. Symptoms include fever, headache, lack of energy, a stiff neck. The most dangerous and frequent serious complication is swelling of the brain (encephalitis). The disease quickly gets worse, and patients may go into a coma within days.

WNV is harder to track because most of those infected about 80 percent have no symptoms, and those with mild symptoms usually recover on their own. According to DPH, between 2000 and 2007, 59 people were reported with WNV infections in the state. Six of those died. About 20 percent who become infected will experience fever, headache and body aches, nausea, vomiting, and sometimes a skin rash. Less than one percent will develop severe illness. People over 50 years of age are at higher risk of serious illness.

WNV causes high mortality in certain birds, like dead crows or blue jays. That's why it's important to report dead birds it's a way of identifying where the virus is present. (Nearly 1,200 have been reported already this year.) You can report such incidents to the DPH from June through September by calling its Public Health Information Line at 866-627-7968. Or contact your local board of health.

Prevention, for both EEE and WNV, is the best course of action. Here are steps public health officials recommend you take:

Avoid outdoor events at dusk and dawn, when mosquitoes are most active.

Repair any holes in screens in windows or doors in your home or garage.

If you see a mosquito indoors, kill it quickly.

Wear socks, long pants, and long-sleeve shirts outdoors, preferably light-colored and loose-fitting. Avoid perfumes and after-shaves; they attract mosquitoes.

Use a repellent with DEET, permethrin, picaridin, or oil of lemon eucalyptus. Do not use DEET on infants under two months, and use in concentrations of 30 percent or less on older children. Do not use oil of lemon eucalyptus on children under three.

Eliminate areas of standing water around your home in such things as containers, flowerpots, recycling bins, wheelbarrows, or clogged gutters. These are breeding grounds for mosquitoes.

DPH has additional information on personal protection, mosquito control in your community, mosquito repellants, and the health effects of pesticides. Visit www.mass.gov/dph or call -866-MASS-WNV (1-866-627-7968).