ANNAPOLIS – The West Nile virus, the newest mosquito-borne virus to enter the Unites States, is here to stay, according to state officials.
The virus has been found in 50 birds in Maryland this year, and although there have been no reports of human infection in Maryland, the virus has caused eight deaths and 80 illnesses in the last two years.
“Most experts do agree that it is going to be here for the long term,” said Cyrus Lesser, Maryland Department of Agriculture mosquito control official.
While it is the only kind of encephalitis imported to the country, it already has become endemic, said federal West Nile coordinator Stephen Ostroff.
The virus is a threat in Maryland, although officials can’t say definitely whether it is circulating locally.
“Right now we feel that most of the birds…were most likely migratory birds,” said Lesser.
Because continuous testing has not shown the virus present in the resident population of mosquitoes in Maryland, Lesser said he doesn’t think that it is circulating locally.
But others aren’t as sure.
“We’re speculating that the crows that were sick are not local crows…but we can’t prove that,” said Cliff Johnson, state public health veterinarian. “We can probably safely say that the virus is here.”
“We know that it’s a lot more difficult to find positive mosquito pools than it is to find positive birds,” said Ostroff. Only about 400 positive mosquito pools have been identified in the United States, he said.
“It’s pretty likely that…while the virus did come in in migratory birds…it probably is getting transmitted to other birds in Maryland,” said Ostroff.
“It will probably significantly change the ecology of wildlife,” he said. It’s long-term impact is unknown, Ostroff said.
Over time the virus may occur in episodic surges, Ostroff predicted, allowing scientists to determine, by charting those fluctuations, the virus’s progress and severity.
In response to infected crows found recently in Anne Arundel and Prince George’s counties, the Department of Agriculture is planning to spray insecticide from trucks in several communities there tomorrow evening.
The goal of the spraying is to reduce the risk of transmission of the virus to humans, said Ostroff. “The purpose of the spraying was never to break the transmission cycle,” he said.
“That strategy seems to have essentially worked,” said Ostroff, who pointed out that the total number of humans infected with the virus nationwide is lower this year.
The state’s program to combat the virus and track the birds will change gears in November, said Johnson. The 24-hour hotline will cut down its operating hours and the state will stop its regular pick-up of dead and sick birds.
It is expected to get cold enough in November to kill most of the mosquitoes, and those that don’t die will go into hiding until it gets warmer.
“It’s going to take two to three nights of a good killing frost,” to kill most of the mosquitoes, said J.B. Hanson, Maryland Department of Health and Mental Hygiene spokesman. That means temperatures will have to be in the upper 20s, said Hanson.
Even then, infected birds may continue to show up. “We don’t know right now how long we’ll keep seeing the body count of birds,” said Hanson.
“We know the virus is here…picking up infected birds is not going to tell us much,” said Johnson. Although some local health departments may decide to pick up birds through the winter, he said.