In the United States, we are currently in the midst of the largest outbreak ever of West Nile Virus (WNV), says the U.S. Centers for Disease Control and Prevention (CDC).
This year, 1,118 cases of WNV in 47 states—including 41 deaths—have been reported, according to the CDC. Almost half of those cases are in Texas.
As of Wednesday, nine cases of human WNV have been reported in Maryland, according to Kimberly Mitchell, chief of rabies and vector-borne diseases at the Maryland Department of Health and Mental Hygiene.
While Mitchell said the agency does not disclose counties where human cases of WNV have been reported, she did say three are in the central Maryland region: one in the DC metro area, one in Western Maryland and four on the Eastern Shore—two on the upper shore and two on the lower shore.
One case has been reported in Anne Arundel County this year, according to the Health Department website.
WNV is spread by infected mosquitoes with a smaller chance of transmission through transfusions, transplants, breastfeeding and from mother to unborn child. The disease has a wide array of symptoms, which may or may not be experienced by those infected—the CDC says around 80 percent of those infected won’t have any symptoms.
Those who are pregnant, very young, have weakened immune systems or are older than 50 are at a higher risk for developing serious issues from the virus, according to the National Institutes of Health. The numbers in Maryland confirm that age is a factor.
“The nine cases [involve people who] range in age from mid 40s to late 70s, as is common,” Mitchell said. “Most of the cases of severe West Nile Disease are in those over the age of 50.”
Of the nine reported cases in Maryland, one person has died, said Mitchell, but because of other health issues the cause of death has not been attributed to WNV. Mitchell urged those older than 50 to take mosquito prevention very seriously.
“We always remind them and everyone to use insect repellent, to repair any damaged window screens and also and this is an important one, they should try to remove or drain any containers on their property that can hold standing water—wading pools, bird bath, old tires,” she said.
Though the number of WNV cases in Maryland is slightly higher than the same time last year when only two cases had been reported, Mitchell said the number is not extreme and is in keeping with the past few years.
“We’ve hit this number slightly sooner than last year—we’re a couple weeks ahead of last year,” she said, adding that in 2011, there were a total of 19 cases reported.
WNV was first detected in the United States in 1999, according to the CDC.
“Our peak year was 2003, when we had 73 human West Nile cases,” said Mitchell.
Since then, efforts by local jurisdictions to reduce mosquito populations, including spraying of neighborhoods, may have decreased the numbers in WNV. In Anne Arundel County, neighborhoods are sprayed if requested by community associations, with individual homeowner opt-out possible. Mosquito control is also keeping private companies, such as Annapolis-based Mosquito-Man, very busy.
"We double our business every year since we started [in 2009] and we did more than that this year," said John Rivers, owner of Mosquito-Man. "We had an extremely dry year, but in this heat and the dryness—I've lived here for 28 years and I've never seen mosquitoes like this."
The Asian tiger mosquito species is "a major pest and threat to public health in Maryland," according to the Maryland Department of Agriculture's website.
"I looked at two houses today and [there were] swarms of Asian tiger mosquitoes all over us," said Rivers.