West Nile Virus Fact Sheet
This page produced by the Continuing
Education-Public Service/Extension group at the University
of Illinois College of Veterinary Medicine
in Urbana.
Go to the College
West Nile Virus page.
West Nile Virus
- 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.
- The list of states in which WNV has been confirmed changes daily. As of
the end of July 2002, WNV had been confirmed in at least 34 states, including
Alabama, Arkansas, Connecticut, Delaware, D.C., Florida, Georgia, Illinois,
Indiana, Iowa, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan,
Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New
York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Dakota,
Tennessee, Texas, Virginia, West Virginia, and Wisconsin.
Transmission of WNV
- This is a blood-borne disease transmitted by blood-sucking insects, primarily
mosquitoes, most commonly the species 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
- By the end of 2001, there had been 149 human cases of WNV reported and
confirmed in the U.S., including 18 fatalities.
- The continued expansion of WNV in the US indicates that it is permanently
established in the Western Hemisphere.
- As of the first week of August 2002, there had been only one human case
of WNV in Illinois. Physicians are asked to report suspected case of WNV to
the Illinois Department of Public Health.
- Infection occurs primarily in the late summer or early fall but in southern
climates, WNV can be transmitted year round.
- Much less than 1 percent of mosquitoes in an infection area are actually
carrying the virus. Less than 1 percent of people who are bitten and become
infected will become severely ill.
- Fatality rates of WNV range from 3 percent to 15 percent of those who become
severely ill and are highest among the elderly and immuno-compromised individuals
(such as cancer and AIDS patients).
- WNV 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 are 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 to 15 days after infection.
- 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 two companies are currently
developing a WNV vaccine.
- If you are bitten by a mosquito, 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 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
- In 2001, 138 birds from seven counties tested positive for WNV. Since sample
collection began on May 1, 2002, one bird, found in Kane County, tested positive.
- If you find a dead bird (especially a crow or blue jay) between May and
October that appears to have died from natural causes, please contact your
local or state health department.
- Contact information for Illinois can be found at: Illinois
Department of Public Health Home Page
- If you are out of state please visit:
Links to
State and Local Government Sites - West Nile Virus - CDC Division of Vector-Borne
Infectious Diseases (DVBID)
- 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.
- Horses can develop encephalitis from WNV infections. The majority of horses
infected recover but some infections have resulted in death.
- By the end of 2001, 738 equine cases in 20 states were reported. Outcomes
were only reported for 470 of these cases, and 33% of these died or were euthanized.
Most infections and deaths occurred in Florida.
- Two cases were reported in Illinois in 2001, including one death.
- 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 killed WNV vaccine for horses was recently approved but its effectiveness
is not yet known. 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 which may provide breeding
areas for mosquitoes
- Dispose of water-holding containers such as discarded tires
- Clean clogged gutters annually
- 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
- Wear long-sleeved shirts and pants when outdoors
- Spray clothing with repellents containing permethrin or DEET and apply
repellent to exposed skin
Created June 5, 2002, from
information compiled by April Finan and Kelly Morgan; updated with information
from Dr. John Andrews.