West Nile virus is a serious mosquito-borne disease affecting much of the U.S.

West Nile virus is a serious disease transmitted to humans by mosquitoes. Every year hundreds of cases are reported, and possibly many hundreds more go undiagnosed or misdiagnosed. The disease can present in a mild fever form or a severe encephalitic form.

Quick West Nile virus background.

• West Nile virus (WNV) is a single-strand RNA virus of the family Flaviviridae, genus Flavivirus, spread from birds to mosquitoes to humans.
• In rare instances, West Nile has been transmitted via blood transfusion and organ transplant.
• Transmission of the virus from mother to fetus or through breastfeeding is being evaluated. Talk to your physician if you are infected and pregnant or breastfeeding.
• West Nile virus cannot be spread from human to human except in the rare and unusual circumstances above.
• Symptoms usually appear 3-14 days after being bitten by an infected mosquito.
• Individuals over age 50 are more likely to develop the severe form of the disease.
• Blood donations are screened for West Nile virus before being distributed.
• The CDC is helping states develop and implement mosquito-control measures to reduce the risk of mosquito-borne diseases such as West Nile virus.
• West Nile virus can kill birds, though most survive infection. If you find a dead bird, do not handle it.
• Pets can also become infected with West Nile virus.
• Horses can become infected. The horse mortality rate is 40%. According to the CDC, there is a vaccine available from veterinarians for horses.

West Nile virus symptoms.

Serious symptoms may last several weeks and neurological effects may even become permanent. Treatment should be sought immediately if these symptoms are exhibited. Hospitalization is usually required for:

• High fever
• Headache
• Neck stiffness
• Stupor
• Disorientation
• Coma
• Tremors
• Convulsions
• Muscle weakness
• Loss of vision
• Numbness
• Paralysis

Milder symptoms may last for a few days to several weeks. These have no specific treatment and usually resolve themselves:

• Fever
• Headache
• Body aches
• Nausea
• Vomiting
• Swollen lymph glands
• Rash on the chest, stomach and back

Diagnosis of West Nile virus

Diagnosis is based on the presence of the disease in the locality (any recent travel should be noted to your physician) and the presence of symptoms. West Nile virus or other arboviral disease should be strongly considered when patients over 50 develop unexplained encephalitis or meningitis during mosquito season. Blood tests may confirm the presence of the disease, though prior infections or recent vaccinations can produce false positive results. Some specific testing guidelines can be found at the CDC website. When the disease is extremely serious, a spinal tap or brain imaging may be taken.

Treatment of West Nile virus

There is no specific course of treatment for West Nile virus. Most cases resolve themselves with no treatment. Even the most severe cases are typically treated only with supportive therapy such as intravenous fluids and painkillers. Interferon is being investigated as a treatment and shows some promise.

Prevention of West Nile virus

Prevention is key when it comes to West Nile virus. You can take a variety of simple measures to greatly reduce your exposure to disease-carrying mosquitoes. These are outlined on our page about mosquitoes.