BERLIN – The once
dreaded West Nile Virus (WNV), which has faded somewhat from the public
consciousness in recent years with fewer occurrences, has been found in
mosquitoes in Maryland for the first time this year.
State officials detected
the first WNV positive mosquito pool for 2010 in Anne Arundel County. The West
Nile infected mosquito pool near Linthicum was discovered after the Maryland
Department of the Agriculture (MDA) collected mosquitoes in that area on July
“It typically appears at
this time in the summer, so we are not surprised with this positive finding,”
said Maryland Agriculture Secretary Buddy Hance. “The confirmation of
virus-positive mosquitoes serves as a reminder to all residents to continue
protecting themselves against mosquito bites and to conduct backyard mosquito
control activities in addition to MDA’s routine surveillance and spray
In 2009, Worcester
County saw the first West Nile Virus positive in Maryland that year, from a
mosquito pool near Pocomoke City, which was also tested in late July of that
Seven of the nine total
mosquito pools in Maryland identified as carrying WNV in 2009 were located in
“Last year, Worcester
County definitely was where the bulk of the mosquito West Nile positive pools
were found,” said Dan Shamberger, an MDA environmental specialist with the
mosquito control service. “That wasn’t anything out of the norm.”
The virus was also found
in a horse on the Eastern Shore in 2009.
The number of positive
samples correlates with the likelihood that the virus will spill over into
horses or people, Shamberger said.
“The fact we found the
one pool tells us there’s some activity. It’s relatively low. There’s no reason
to be concerned right now,” said Shamberger.
MDA’s mosquito control
staff sprays for adult mosquitoes in Worcester County, beginning in mid-May,
with larviciding also used to control sub-adults.
This week, the state of
Delaware also reported the presence of WNV west of Wilmington, detected through
a sentinel chicken program.
Delaware’s Department of
Natural Resources keeps 24 chicken sentinel stations around the state. The
state tests the chickens’ blood ever two weeks for WNV and Eastern Equine
Encephalitis (EEE) antibodies, which show that the chickens have been exposed
to those mosquito-borne diseases.
Delaware’s WNV positive
blood sample was taken from a chicken on July 19.
Across the country, by
the third week of July, only 26 WNV cases have been reported. Half of those
cases occurred in Arizona.
The WNV season is just
beginning, said Delaware Mosquito Control Section Administrator William
Meredith, and will last into October, when cooler weather sets in.
Weather conditions could
provide more opportunities for mosquito borne disease to spread.
“If this year’s hotter
than normal conditions continue, there is some concern that the growth and
replication of West Nile and EEE viruses may increase in mosquito hosts,
leading to greater probability for virus transmission,” Meredith said.
“However, if dry conditions also continue, mosquito breeding may be reduced,
thus also reducing the number of mosquito hosts to transmit these viruses.”
Shamberger said MDA
staff expected a healthy mosquito population this year after a wet spring, but
the subsequent hot and dry weather of the summer reduced that.
There is a relatively
low number of mosquitoes statewide, he said. In a dry year, mosquito problems
are typically more localized to certain communities or areas. MDA staff checks
mosquito populations using traps and landing rates.
Maryland and Delaware
officials said that their states would continue mosquito control activities.
remains especially important to decreasing the risk of infection with all mosquito-borne
diseases,” said MDA Mosquito Control Chief Michael Cantwell.
Few mosquitoes actually
pose a threat of WNV or EEE transmission, state officials said, because they
are not infected.
Just 20 percent of
people who do become infected with WNV will develop any symptoms at all,
usually mild ones such as fever, body aches and headaches.
No more than 1 percent
of those bitten by a WNV carrying mosquito will develop severe symptoms, such
as a very high fever. Those over 50 or with a pre-existing immune system issue
are the most vulnerable to WNV.
There is no human
vaccine for WNV or EEE, although working vaccines exist for horses and ratites
such as emus.