Who's at risk?
Anyone who is outdoors when infected mosquitoes are present is at risk, Christoffel says. But even in areas where transmission of the virus is occurring, human infection is "relatively rare," according to the CDC.
West Nile virus is not spread from person to person. Mosquitoes get infected with the virus when they ingest blood of a bird carrying it. When the mosquito bites its next victim - bird, human or animal - it transmits the virus through its saliva, according to CDC.
Additionally, a recent investigation has confirmed that the virus can be transmitted through organ transplant, and there has been one case of transplacental transmission (mother-to-child). Two cases of infection of laboratory workers were reported recently.
People older than 50 are at higher risk for West Nile encephalitis, the severe form of the disease, according to the CDC.
More than 90 percent of those exposed will have no symptoms, Christoffel says.
CDC estimates that 20 percent of people infected will develop mild symptoms, including fever, head and body aches, swollen lymph glands and occasionally a skin rash on the trunk of the body.
The estimate for the number of people who will develop West Nile encephalitis is one in 150. Symptoms can include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.
A blood test can confirm the presence of the virus, but there is no specific treatment.
Although several drug companies are working toward developing a vaccine against West Nile encephalitis, none is yet available, according to CDC.
The key to not becoming infected with the virus is to avoid being bitten by an infected mosquito.
The prospects for this year's mosquito season, which Christoffel says typically runs from May to October, are good - for mosquitoes.
The drought officially is over, says Cyrus Lesser, chief of the mosquito control section, Maryland Department of Agriculture. Between the snowmelt and above normal rainfall, there will be more water for mosquitoes, Lesser says. Mosquitoes - there are 62 different species in Maryland - lay their eggs in standing water. Some of those mosquito species are very selective in their choice of victims, Lesser says. One bites only frogs, for example. About a dozen species are of particular concern in Maryland, he adds.
Dead birds will not be collected for West Nile virus testing in Washington County, as they have been for a few years, Christoffel says. Birds are a warning system. Christoffel compares them to canaries in the coal mines. The presence of the virus already has been established. "We know it's here," Christoffel says.
Washington County officials met last week to talk about measures to control mosquitoes.
Infection is rare, and measures to prevent mosquito-breeding are under way. Locally, Washington County Engineering and Transportation departments monitor storm-water management ponds and prevent mosquito eggs from hatching by tossing larvicide - disk-shaped pesticide called mosquito dunks - into the water. Developers and builders are responsible for monitoring standing water at construction sites, says Laurie Bucher, director of Washington County Health Department's environmental health division. Dunks, which cost about $9 for a packet of six, can be purchased at hardware and home improvement stores.
Twelve individual communities, including Hancock and Funkstown, have sprayed, Bucher says. The state also will be doing some spraying, Lesser says.
West Nile virus and its transmission by mosquitoes is something to be aware of, says Eric LeMasters, horticulture consultant in Washington County with the Cooperative Extension Service of the University of Maryland.
"But, it's got to be kept in perspective," he says.
The 277 deaths caused by West Nile virus pale in comparison to the roughly 20,000 deaths nationwide attributed to influenza in 2002.