It is an infection caused by West Nile Virus (WNV), which is spread to people by the bite of a mosquito infected with the virus. Experts believe that WNV has established itself as a seasonal epidemic in North America that flares up in the summer and continues into the fall. It is usually considered a virus of birds, but people and other animals can be accidental hosts. In people, the disease usually causes only a mild illness, but may cause encephalitis (swelling of the brain), meningitis (swelling of the lining of the brain), or even death in rare cases. The virus is named after the West Nile region of Uganda where the virus was first identified.
No. This virus was first identified in 1937 in Uganda, Africa. Prior to 1999, the virus had only been identified in Africa, Europe, the Middle East, and Asia. WNV was first detected in the United States in 1999, when 62 cases and seven deaths from WNV were reported in the New York City area. In 2002, the United States had 4,156 laboratory-positive cases with 284 deaths.
Anyone can get infected with WNV if bitten by an infected mosquito. More severe infections are seen in the elderly and those with a weakened immune system.
WNV is primarily spread by the bite of infected mosquitoes. Mosquitoes become infected by biting a bird that carries the virus. The next time the mosquito feeds the virus is injected into the human. WNV cannot be spread directly to humans from birds or animals or through human ingestion of infected animals or birds. WNV is not spread by person-to-person contact such as touching, kissing, or caring for someone who is infected. In a very small number of cases, WNV also has spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.
Infected mosquitoes are the primary source of the virus and caused the recent outbreaks in the United States. There is no evidence that other insects or ticks transmit WNV.
Most people infected with WNV do not become ill. People with a mild infection may experience fever, headache, nausea, vomiting, eye pain, muscle aches, joint pain, a rash on the trunk and often swollen lymph nodes. In severe cases symptoms include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and/or paralysis. Most of these severe symptoms are due to inflammation of the brain. The infection can be fatal, particularly in the elderly and the immunocompromised.
Symptoms usually occur 3 to 15 days after a WNV-infected mosquito bites a person. Being bitten by an infected mosquito will not necessarily make you sick. Most people who are infected with West Nile Virus have no symptoms or have only mild illness.
No. Most mosquitoes are not infected with WNV. Infections generally occur during warm weather months when mosquitoes are most active. However, even in areas where WNV occurs, only a small proportion of the mosquitoes are likely to be infected.
If you develop signs of encephalitis, with fever, muscle weakness, and confusion, you should seek medical care immediately.
Prior infection with WNV is thought to provide lifelong immunity to the virus, although protection may decrease in later years.
There is no specific treatment for WNV infection. Mild WNV illness improves with no treatment. However, a physician may prescribe medications to relieve the symptoms of the illness if necessary. In severe cases hospitalization may be required to receive supportive treatment.
No WNV vaccine for humans exists at this time. A reliable vaccine for horses does exist…contact your local veterinarian for more information.
West Nile virus case report numbers published by KDHE are based upon the results of confirmatory testing performed by the state Division of Health and Environmental Laboratories (DHEL). Such testing may be performed only at the request of a physician who is treating a patient with specific signs and symptoms of meningitis or encephalitis.
These signs and symptoms may include confusion, speech difficulties, loss of coordination, hearing and vision impairments, marked behavioral or mood changes and severe or prolonged dizziness or headache.
There is currently no evidence that WNV can be spread directly from an infected bird to people. However, dead birds can carry other diseases and should not be handled with bare hands. Use gloves to place dead birds into plastic bags and then placed into outdoor trash or turn into the local designated collection site.
Horses and other animals can be infected with WNV from the bite of an infected mosquito. Most horses infected with WNV recover, but there have been horses in the United States that have died as a result of WNV infection. A vaccine against WNV is available for horses…for more information, please contact your local veterinarian. Although other animals may be infected with WNV, they may not show signs of the disease. There is no evidence that people can get WNV directly from animals or that animals can spread the disease to other animals.
A recent CDC investigation has confirmed that WNV be transmitted through blood transfusion and organ transplantation.
No. There is no risk of WNV infection for people who give blood. Blood saves lives and is always needed, especially during the summer months. Because donating blood is safe, we encourage blood donation now and in the future. We also encourage all donors to truthfully answer the questions asked by the blood bank to make sure you are fit to donate on a given day. The benefits of receiving needed transfusions or transplants outweigh the potential risk for WNV infection. However, doctors and their patients who need blood transfusions or organ transplants should be aware of the risk for WNV infection.
Yes. WNV infections do not last very long. The virus is in the blood for a very short time, and the human body fights and usually eliminates the virus in a few days. When a person’s body clears the virus, they develop an antibody (a protein that helps fight infections). The antibody will be transfused and help keep the recipient from getting a WNV in the future, by helping to keep the virus out of the blood. Blood centers will take precautions to be sure that donors who have been diagnosed with WNV infection have fully recovered before allowing donation.
You should be aware of the potential risk for WNV infection and the need to monitor your health. If you have symptoms of WNV disease or other concerns you should contact your physician. A large number of WNV infections due to mosquito bites occurred among people in the United States during 2002. Some of these people also received blood transfusions and/or organ transplantations. If a patient who recently received a blood transfusion or organ transplantation develops a WNV infection, that does not necessarily mean that the transfusion/transplantation was the source of infection. In the known transfusion-infection cases, onset of illness was between 2 and 21 days (median 11 days) after the implicated transfusion. If you have symptoms of WNV or other concerns you should contact your physician.
Reducing mosquito populations will also reduce mosquito bites. In some communities, public funded surveillance and control programs reduce mosquito populations by eliminating mosquito breeding habitat, mosquito larvae or adults. You can also take measures in your own yard or on your property to eliminate standing, stagnant water where mosquitoes breed. Mosquitoes most likely to carry WNV will not breed in fresh water or running water.
Mosquitoes most likely to carry WNV breed in standing, stagnant water. Any container or area where water can collect is a potential breeding ground for mosquitoes, including unused tires, buckets, toys, clogged gutters, birdbaths, and livestock tanks. Turning out the water in containers or replacing/replenishing existing water every three days will interrupt the mosquito life cycle.
Several websites with helpful information have been developed to answer West Nile Virus questions: