West Nile Virus: What You Should Know

The West Nile Virus (WNV), commonly found in Africa, West Asia, and the Middle East, has emerged in recent years in North America. Since 1999 it has been reported in all states, but Hawaii, Alaska, and Oregon. WNV is established as a seasonal epidemic that flares up in the summer and continues into the fall. The development of the disease in states seems to follow a pattern. It is believed that once infected, people have long-lasting immunity.

If someone is infected with West Nile virus (WNV) they will have one of three outcomes:

• no symptoms (most likely);
• West Nile Fever (in about 20 percent of infected people); or
• severe West Nile disease such as meningitis or encephalitis (in less than 1 percent of cases).

The most significant risk factor for developing severe disease is advanced age. If you develop a high fever with severe headache consult your health care provider.

How is it spread?

The virus is spread by mosquito bites to people and animals. It is not known to be spread from animal to person. There is at least one documented case of a pregnant woman passing the infection to her unborn baby. The possibility of passing the infection through breast milk is currently being investigated. In temperate areas (northern states), the virus is spread primarily in the late summer or early fall. Where temperatures are milder (southern climates), West Nile Virus can be transmitted year round. One of the species of mosquitoes found to carry West Nile virus is the Culex species, which survives through the winter, or “overwinters,” in the adult stage. This means that the virus can survive along with the mosquitoes. This species was responsible for the widespread transmission of West Nile virus in the United States during the summer of 2000.

Do animals get West Nile virus?

The virus can infect humans, birds, horses and some other mammals. Some wild birds are particularly susceptible to infection with West Nile virus. Mosquitoes feed on the infected birds and then spread the infection to another bird, person, or animal that the mosquito bites. An increase in the number of dead birds may indicate that mosquitoes in the area are carrying the virus. Persons who find a dead bird (especially a crow, raven, magpie, jay or hawk) are encouraged to report it to the Department of Health Services through the West Nile Virus Dead Bird Hotline (877-WNV-BIRD).

What are the symptoms?

Symptoms generally occur three to 15 days after exposure. The infection may be asymptomatic or mildly symptomatic with flu-like symptoms such as fever, headache and body aches which last a few days. There do not appear to be long-term health issues associated with the virus. Rarely, the virus can cause encephalitis (inflammation of the brain) and death. The risk of contracting the virus or becoming seriously ill from it is very low in humans.

How is West Nile virus treated?

There is no specific treatment for West Nile virus. The rare person who develops West Nile encephalitis requires hospitalization and supportive therapy.