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West Nile Virus (WNV) is a type of virus that causes an encephalitis
(swelling of the brain) that can sometimes be fatal. WNV was first
documented in North America in 1999.
Transmission of WNV
This is a blood-borne disease transmitted by blood-sucking insects,
primarily mosquitoes, most commonly the house mosquito (Culex pipiens).
Mosquitoes become infected after feeding on the blood of a bird
that is carrying the virus. Infected mosquitoes may then transmit
WNV to humans and other animals.
WNV and Humans
The continued expansion of WNV in the US indicates that it is permanently
established in the Western Hemisphere.
Infection occurs primarily in the late summer or early fall but
in southern climates, WNV can be transmitted year round. Much less
than 1% of mosquitoes in an infection area are actually carrying
the virus. Less than 1% of people who are bitten and become infected
will become severely ill.
WNV generally cannot be transmitted directly from animal to person,
from animal to animal, or from person to person. People over 50
years of age are at highest risk. The virus acts by crossing the
blood-brain barrier, where it interferes with normal central nervous
system functions and causes inflammation of brain tissue.
Signs of mild infections include fever, headache, body aches, skin
rash, and swollen lymph nodes. Severe infections can additionally
cause neck stiffness, stupor, disorientation, coma, tremors, convulsions,
muscle weakness, paralysis, and sometimes death. Signs will occur
3-15 days after infection.
Fatality rates of WNV range from 3-15% of those infected and are
highest among the elderly and immuno-compromised individuals (such
as cancer and AIDS patients). WNV is diagnosed by obtaining a blood
sample, which is then sent to a commercial or public health laboratory.
No specific therapy is available for WNV, but severe cases are hospitalized
and receive IV fluids and respiratory support. While hospitalized,
secondary infections can be prevented and the patient can receive
good nursing care.
There is no vaccine available for humans but companies are currently
developing a WNV vaccine. If a mosquito bites you, you do not need
to see a doctor unless you exhibit signs of infection such as high
fever, confusion, muscle weakness or severe headaches. Individuals
with mild influenza-like signs are likely to recover completely
and do not require any specific medication or laboratory testing.
Proper cooking kills the WNV; therefore, there is no danger associated
with eating thoroughly cooked wild game such as duck, geese and
turkey that might be infected.
WNV and Other Animals
Many mammals can be infected with West Nile Virus, including horses,
cats, bats, dogs, squirrels, chipmunks, skunks, and domestic rabbits.
Horses infected with WNV can develop encephalitis. Also, certain
birds, especially crows, blue jays, and hunting birds, such as hawks
and falcons, can become ill and die with WNV infection.
WNV has been identified in more than 103 species of birds, including
captive, exotic, and those native to the US. Knowledge of infected
birds in a community allows increased public awareness of the possibility
of WNV infection in the area.
Cases of WNV have been reported in dogs and cats but infection
rates in epidemic areas are low. WNV does not usually cause severe
illness in dogs and cats. There is NO reason to destroy an animal
because it has been infected with WNV. Full recovery is likely and
direct transmission of the virus to you or your other pets is unlikely.
Dogs and cats could possibly become infected by eating dead infected
animals such as birds, but this is unproven.
WNV and Horses
Horses can develop encephalitis from WNV infections. The majority
of horses infected recover but death is common. Signs of WNV infection
in horses include listlessness, incoordination, weakness, recumbency,
and muscle tremors.
Signs of WNV may be similar to those of rabies, equine herpesvirus,
equine protozoal myeloencephalitis, eastern equine encephalitis
(EEE), western equine encephalitis (WEE), or Venezuelan equine encephalitis
(VEE). WNV cannot be transmitted to a person caring for a horse
infected with WNV.
There is no documented evidence that WNV is transmitted between
horses in neighboring stalls. However, horses with suspected WNV
should be isolated from mosquitoes, if possible. Horses that have
been vaccinated against eastern equine encephalitis (EEE), western
equine encephalitis (WEE), or Venezuelan equine encephalitis (VEE),
are not protected against WNV.
A WNV vaccine for horses is available. Please contact your veterinarian
for more information.
You can protect your horses from mosquitoes by providing them with
screened shelters (eliminate mosquitoes from the inside of the structure
before screening it in). Using insect repellents and keeping horses
indoors at night may reduce risk of infection.
Preventing WNV Infection at Home
- Remove all man-made sources of stagnant water that may provide
breeding areas for mosquitoes and larva development. Water should
not stand for more than 7 days.
- Dispose of water-holding containers such as old tires. Make
sure that swings made from tires have drainage holes in the bottom
to allow water to drain.
- Clean clogged gutters regularly, especially in the early spring
and fall.
- Turn over plastic wading pools or wheelbarrows when not in use.
- Do not allow water to stagnate in bird baths/change the water
at least once a week.
- Aerate ornamental pools or stock them with fish that eat mosquito
larvae.
- Clean and chlorinate swimming pools and drain excess water from
pool covers.
- Clean livestock watering troughs regularly.
- Stay indoors at dawn and early evening.
- Make sure windows are covered securely with screens. Repair
damaged window screens. Caulk crevices around doors and windows
to prevent mosquitoes from entering the house.
- Wear long-sleeved shirts and pants when outdoors.
- Spray clothing with repellents containing permethrin or DEET
and apply repellent to exposed skin.
- Regularly check on the elderly and those that tend to keep windows
open to allow for cooling during the summer.
This information provided by:
David Robson, Extension Educator, Horticulture, Springfield Center
Rhonda Ferree, Unit Leader, Fulton County
Dr. Phil Nixon, Extension Entomologist
Modified by UI Extension. Based on information
from April Finan and Kelly Morgan.
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