Announcement of June 26 WNV Forum * WNV Fact Sheet * WNV FAQs
This page produced by the Continuing Education-Public Service/Extension group at the University of Illinois College of Veterinary Medicine in Urbana.
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.
WNV has been confirmed in 27 states including Alabama, Arkansas, Connecticut, Delaware, D.C., Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Mississippi, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania. Rhode Island, Tennessee, Virginia, and Wisconsin.
The continued expansion of WNV in the US indicates that it is permanently established in the Western Hemisphere. The virus is maintained within bird and mosquito populations.
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.
Yes. By the end of 2001, there had been 149 human cases of WNV reported and confirmed in the US, including 18 fatalities.
There have been no human cases of WNV in Illinois. Physicians are asked to report suspected case of WNV to the Illinois Department of Public Health.
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.
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 develop severe illness.
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).
People over 50 years of age are at highest risk.
The virus crosses the blood-brain barrier where it interferes with normal central nervous system functions and causes inflammation (swelling) of brain tissue.
Mild infections may cause 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.
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.
No. There is no vaccine available for humans but two companies are currently developing a WNV vaccine.
Other animals can shows signs of illness when infected with WNV. Horses exposed to 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:
If you are out of state please visit:
Knowledge of infected birds in a community allows increased public awareness of the possibility of WNV infection in the area.
Proper cooking kills the WNV, therefore, there is no danger associated with eating thoroughly cooked wild game that might be infected.
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.
No. WNV cannot be transmitted directly from animal to person, from animal to animal, or from person to person.
Dogs and cats could possibly become infected by eating dead infected animals such as birds, but this is unproven.
Horses can also 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.
Horses will show listlessness, incoordination, weakness, recumbency, and muscle tremors. Fever is not usually observed. 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).
No. WNV cannot be transmitted by direct animal-to-person contact.
No. There is no documented evidence that WNV is transmitted between horses. However, horses with suspected WNV should be isolated from mosquitoes, if possible.
No. These vaccines will not protect horses against WNV infection.
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 WNV by preventing their exposure to mosquitoes, such as 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 help reduce the risk of infection.
Many mammals can be infected with West Nile Virus, including horses, cats, bats, dogs, squirrels, chipmunks, skunks, and domestic rabbits.
Created June 5, 2002, from information compiled by April Finan and Kelly Morgan.