West
Nile Virus (WNV) is once again in the news, with outbreaks reported in
Texas, Mississippi, Louisiana, South Dakota and Oklahoma. Here in Georgia,
although we are seeing human cases of WNV earlier than usual, the number of
cases we have reported is about average for the state. As of Aug. 24, DPH
identified 21 confirmed cases of WNV in the state. Three cases have been
fatal.
The CDC is reporting the worst WNV year in the country since 2004. This is
due, in part, to the mild winter and early spring experienced in much of the
country. The primary vector of WNV in Georgia is
Culex quinquefasciatus
(Southern house mosquito). Early warm weather allows these mosquitoes to
emerge and begin blood feeding earlier, transmitting the virus to birds as
they feed. The earlier in the year this occurs, the more birds are likely
to become viral positive, the greater the chance that more mosquitoes will
become viral positive, and the higher the risk to humans bitten by these
mosquitoes.
Culex quinquefasciatus is primarily found in older urban and
suburban areas. The female mosquito lays her eggs in organically polluted
water in containers such as catch basins, tires, retention and detention
ponds, sewer overflows, and in rural areas, farm runoff ponds. Because this
mosquito is most often associated with more densely populated areas, people
are at highest risk in urban and suburban areas with older infrastructure
that provides plentiful breeding sites.
Mosquito surveillance provides information about the number and species of
mosquitoes in any given area. In the past, these mosquitoes were pooled and
sent to the Southeastern Cooperative Wildlife Disease Study (SCWDS) at UGA
for testing. Unfortunately budget cuts have eliminated surveillance and
testing in much of Georgia.
Because this mosquito species emerges as an adult asynchronously (a few at a
time) it is a difficult mosquito to control and needs an integrated approach
that includes surveillance, larviciding, source reduction, education and
adulticiding to keep as many older mosquitoes out of the population as
possible. It is these older mosquitoes that are more likely to have become
infected with WNV.
The key to reducing WNV risk is education. People should eliminate standing
water and wear repellent, according to label instructions. It is also
important to support integrated mosquito control efforts as well as testing
of mosquitoes for WNV and other arboviral diseases.
-Story by Rosmarie Kelly, DPH Entomologist, Vector-Borne & Zoonotic
Diseases Team,Acute Disease Epidemiology Section
