Wetlands And West Nile Virus

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History
The first documented case of West Nile infection in humans occurred in Uganda
in 1937. Originally endemic to Africa, western Asia and the Middle East, the
virus has since stretched into Australia and parts of Europe. In 1999, West Nile
crossed the Atlantic and struck New York City, causing 62 illnesses and 7 deaths.
The US strain of West Nile is genetically similar to a variety found in Israel,
which suggests that international travel—perhaps stowaway mosquitoes or
unaware human carriers—brought the virus to the Western hemisphere.
Epidemiology
The Centers for Disease Control and Prevention has identified approximately
4,000 human cases in 40 states, with Illinois, Ohio, Michigan and Louisiana
posting the greatest numbers. The documented cases do not account for all
infections, as 80% of infections pass unnoticed. Less than 1% of infections
results in severe neurological illness, such as meningitis and/or encephalitis. In
2002, West Nile caused 284 human deaths in the United States. In the same
year, more than 15,000 horses were diagnosed with West Nile virus; 33% died
or were euthanized. A vaccine exists for horses and is 94% effective.
Medical Facts
West Nile virus belongs to the flavivirus genus, which includes yellow fever and St. Louis encephalitis. Following
infection, the virus incubates 3-14 days. The vast majority of infected people do not exhibit any symptoms.
Protect Your Home
Eliminate stagnant water in cans,
buckets, tires, pots. Change water
frequently in bird baths and water
bowls.
Remove leaves and other
blockages from roof gutters.

Install and repair screens on doors
and windows.

Be wary of electric bug zappers.
Biting insects make up less than
1% of insects killed by such
devices. Bug zappers also kill
beneficial insects, including
mosqito predators.
Symptoms
Those who develop West Nile fever have
mild, flu-like symptoms that usuallly
subside after 3 to 6 days. The relatively
few patients who fall seriously ill may
experience severe muscle weakness and
develop meningitis and/or encephalitis.
These patients tend to experience
persistent symptoms for more than a year.
The elderly and the immuno-suppressed
are at greatest risk of suffering health
complications from West Nile virus.
I Diagnosis
I Generally, diagnostic tests do not search for the virus in the body;
• instead, they locate antibodies that fight the virus. Because many
' flaviviruses elicit the production of similar antibodies, West Nile
5 infection is easily confused with other flaviviral infections, such as St.
' Louis encephalitis. People with vaccinations for other flaviviruses (e.g.,
: yellow fever) may also falsely test positive for West Nile.

Treatment
', Because no cure exists for West Nile in humans, treatment is supportive;
doctors help the immune system tackle the infection. Antibiotics are
ineffective. A vaccine is expected in a few years.
Mosquito Vectors
Mosquitoes are the primary vectors of West Nile, meaning they
carry the virus from host to host. Nectar is their primary food
source. Only females take blood in order to develop their eggs;
males do not bite. Colder months reduce mosquito activity, but the
virus persists in dormant mosquitoes and eggs that survive winter.
Cu/ex pip/ens
Flight range: '/i mile - 1 mile
Feeding times: dusk to dawn
Habitat: stagnant pools, artificial containers
Seasons: late Spring to Fall
Cu/ex salinarius
Flight range: up to 5 miles
Feeding times: dusk to dawn
Habitat: fresh, brackish water near coast
Seasons: early spring to November
Bothersome for duck hunters in the fall
The Centers for Disease Control and Prevention reports that 37 mosquito
species in the United States have tested positive for West Nile virus. The
most common carriers are the Northern House mosquito (Culex pipiens)
and the Southern House mosquito (Culex quinquefasdatus). Because it
readily feeds on humans, Culex salinarius is an important vector as well.
In western states, Culex tarsalis plays a prominent role in transmission.
Cu/ex mosquito
Courtesy or CDC

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...that healthy wetlands are not unmitigated
mosquito factories. Healthy wetlands
provide habitat for mosquito-eating fish,
amphibians, insects and birds, all of which
help limit mosquito populations (and none
of which exist in backyard pots or buckets).
Bats also help reduce mosquitoes.
According to Bats Conservation
International (www.batcon.org), a single bat
can catch 100 insects per hour. Protecting
wetlands is more important than ever, for
in addition to their well-known benefits—
water purification, wildlife habitat,
floodwater retention—healthy wetlands
have natural mosquito controls.
Are Wetlands a Threat?
The principal mosquito carriers of West Nile virus do not prefer
most wetlands. Culex pipiens and Culex quinquefasciatus reach
greatest numbers in large urban centers, breeding easily in
artificial containers—birdbaths, discarded tires, buckets—and in
human-created environments, such as clogged gutters, animal
waste lagoons and sewage effluent. Adapted to polluted habitats,
these Culex species generally avoid swamps and salt marshes
altogether. Culex salinarius prefers fresh or brackish water near
coasts and is particularly fond of salt marshes that have been
converted into freshwater impoundments.

Contaminated water and degraded wetlands provide ideal
habitat for mosquitoes that carry West Nile virus. High nutrient
loads spur microbial growth and cause harmful algal blooms,
which are sources of food for mosquito larvae. Filling or
draining wetlands may increase mosquito outbreaks, as puddles
that lack mosquito predators may form after rains or floods.
Therefore, communities can help control mosquito populations
by protecting wetlands and other shallow waters from pollution
and degradation. Wetland Restoration
and Mosquito Reduction in New Hampshire
Prior to its restoration in 1999, the two-acre Edmond Avenue wetland was
in critical condition. Residential development near Portsmouth, New
Hampshire, had partially filled the wetland, and urban and stormwater
runoff had contaminated the water. Increased sedimentation had reduced
the extent of open water, and invasive plants choked native species.

By 1996, the continued degradation of the Edmond Avenue wetland
transformed the ecosystem into a major breeding site for mosquitoes,
including the Culex species primarily responsible for West Nile
transmission. From 1996-1999, the application,
of mosquito larvicides and sprays jumped to 4-
5 times per year, a four-fold increase from the
previous 15 years.

Since its restoration in 1999, the Edmond Avenue
wetland no longer requires mosquito control measures.
The restored wetland lacks stagnant depressions and is
deep enough in some areas to support fish that eat
mosquitoes. Wave action also disrupts mosquito breeding.
Results have been astonishing—a near 100% reduction
in mosquito habitat and the virtual elimination of
Culex species, not to mention improved water
quality and bird habitat.
Broadleaf arrowhead

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           References  for
   American At'occi
Bernard, K. July-August 2001. West Nile virus infection in birds and
mosquitoes, New York State, 2000. Emerging Infectious Diseases 7(4).

Crans, Wayne J. Products and Promotions That Have Limited Value for
Mosquito Control. Rutgers, the State University of New Jersey.

Eidson M., Komar N., Sorhage F., Nelson R., Talbot T., Mostashari F., et al.
2001. Crow deaths as a sentinel surveillance system for West Nile virus in the
northeastern United States, 1999. Emerging Infectious Diseases 7.

Fauci, A., Director of National Institute of Allergy and  Infectious Diseases.
September 24, 2002. Congressional testimony before Senate subcommittee on
Oversight of Government Management.

Giladi M., et. al. 2001. West Nile encephalitis in Israel, 1999: the New York
connection. Emerging Infectious Diseases 7.

Goddard L.B., et al. December 2002. Vector competence of California
mosquitoes for West Nile virus. Emerging Infectious Diseases 8.

Mostashari E, et. al. 2001. Epidemic West Nile encephalitis, New York, 1999:
results of a household-based seroepidemiological survey. Lancet 358:261-4.

Petersen L., Marfin A. 2002. West Nile virus: a primer for the clinician.
Annals of Internal Medicine 137:173-179.

Smithburn K., Hughes T., Burke A., Paul J. 1940. A neurotropic virus isolated
from the blood of a native of Uganda. American Journal of Tropical Medicine
and Hygiene. 20:471-92.
     Protect Your Community

     Report unusual  bird deaths to
     officials at appropriate focal, county
     or state agencies.

     Protect wetlands from pollution,
     including runoff from f«i*r*s, lawns
     and roads, since contaminated
     water attracts mosq«|toes that carry
     West Nile.       ,"

     Remember that stocking wetlands
     and ponds  with fitft that eat
     mosquitoes may fcave unintended
     ecological consequences.

     Design stormwater catchments and
     constructed  welifhds  so that
     mosquito breeding l^rniriirnized.

     Try larvicfdes befori gA^Mddes, if
     possible "and-'nes^&|fiy|r since
     larvicides more .<$fci$$ijij$f, control
     mosquitoes.   Ctfff'ferity'•'.  follow
     instructions on
            U.L
  on  the Internet
  Centers for Disease Control and Prevention, West Nile Virus
  http://www.cdc.gov/ncidod/dvbid/westnile

  Maps of West Nile Distribution in the United States
  http://cindi.usgs.gov/hazard/event/west_nile/west_nile.html

  State and Regional Information
  http://westnilevirus.nbii.gov/states/index.html

  Cornell University, Center for the Environment
  http://www.cfe.cornell.edu/erap/WNV/
Health information, fact sheets,
latest case counts

Locations of infections in humans,
birds and other animals

State by state information on
infections, surveillance and control

Updates on West Nile, sources and
links for public and professionals

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