Health officials are urging residents to take precautions against mosquito bites that could transmit the West Nile virus or other infections after heavy rains last week improved breeding conditions for the insects.
Fairfax County Health Department officials said yesterday that they found the first indication of West Nile in a mosquito pool that tested positive for the virus.
“This is a reminder that West Nile virus is still active in Fairfax County and that now is the time for people to pay close attention to eliminating mosquito-breeding areas before more mosquitoes become infected, particularly after the large amount of rain that we received this past week,” said Dr. Gloria Addo-Ayensu, director of the county’s health department.
County health officials have treated more than 30,000 storm drains with larvicide since May. More work is scheduled throughout the mosquito season, which typically ends in October.
“We are closely monitoring mosquitoes this year and have tested more than 31,000 so far, looking for West Nile and other arboviruses,” said Jorge Arias, a county environmental-health entomologist.
He said many mosquitoes did not survive the rain last week but new populations are about to hatch.
As a result, officials are telling residents to eliminate standing water in which mosquitoes lay their eggs.
Mr. Arias said the Asian tiger mosquito in particular would flourish in the warm, wet conditions. It breeds in clean water in “artificial containers” such as decks, tires and garbage-can lids, he said.
Montgomery County does not conduct a lot of surveillance for the virus because “we know it’s endemic,” said Mary Anderson, a spokeswoman for the county’s Department of Health and Human Services. “It’s here every year. We know that mosquitoes are going to be infected.”
The Maryland Department of Agriculture regularly sprays residential areas with pesticides. The program is for residential areas that request help and agree to share the cost of the program, the agency said.
Mosquito bites can be prevented by wearing long sleeves and long pants to shield the skin and by using insect repellant that has DEET as an active ingredient. Mosquitoes are most active during the early morning and at sunset, health specialists say.
Most people who contract the West Nile virus do not experience symptoms, said the federal Centers for Disease Control and Prevention (CDC). Of those who become infected with the virus, 20 percent may contract West Nile fever, which can include a high temperature, headaches, body aches, fatigue and rashes.
The most severe and rarest of cases is the neuroinvasive disease, which attacks the nervous system and is most common in those 50 and older.
No treatment or vaccine is available. Only the symptoms of the diseases can be treated.
The CDC has reported four cases of the neuroinvasive disease in the United States, but none in Maryland, Virginia or the District.