What is West Nile Virus?

West Nile is a mosquito-borne virus first discovered in the United States in 1999. The first reported illness was found in New York City. The virus has the ability to infect people, mosquitoes, certain types of birds, horses and other animals. Not all species of mosquitoes carry the virus.

How is it spread?

West Nile is spread by the bite of an infected mosquito. When a mosquito bites an infected bird with the West Nile virus, the virus enters the mosquito's bloodstream and circulates for a few days before settling in the salivary glands. When the infected mosquito bites and animal or a human, the virus then enters the host’s bloodstream where it may cause serious illness. The incubation period; period between when you are bitten by an infected mosquito and the appearance of signs and symptoms of illness, ranges from 2 to 14 days. The virus is not spread through person to person contact or animal to animal contact. Following transmission by an infected mosquito, West Nile virus multiplies in the person’s blood system and crosses the blood-brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and causes inflammation of brain tissues.

What are the symptoms?

West Nile has 3 different effects on humans. The first is asymptomatic. This means the infected individual shows no symptoms of infection. Most people infected with the West Nile virus fit into this category. The second stage is West Nile Fever. Only 20% develop symptoms that include fever, fatigue, skin rash, diarrhea, nausea, headache, vomiting, swollen lymph glands, and muscle or joint pains. These symptoms can last a few days to several weeks. The third and more severe category is West Nile encephalitis or West Nile Meningitis. Less than 1 percent of infected people will develop a more serious illness with symptoms that include headache, high fever, stiff neck, disorientation, convulsions, tremors, muscle weakness, lack of coordination, pain, and coma. Severe cases of the virus may lead to paralysis, coma, or death.

Even if you are infected your risk of developing a serious West Nile virus related illness is extremely small. Most people who do become sick recover fully. Symptoms normally begin to appear 3 to 15 days after the mosquito bite occurs. People age 50 and older or people with weak immune systems are more likely to develop severe symptoms from the West Nile virus.

How is it treated?

There is no specific treatment for a West Nile infection. In serious cases treatment may involve hospitalization where patients can receive supportive treatment including intravenous fluids, respiratory support, prevention of secondary infections, and nursing care.

Currently there is no vaccine to protect humans from West Nile. The best defense against disease is to control mosquito populations, monitor for the presence of the virus, and prevent mosquito bites.

Personal Protection

• Avoid exposure to mosquitoes. Stay inside during the peak biting times (dawn dusk and early evening)
• Wear long sleeves and pants. Avoid dark clothing.
• Wear mosquito repellents when outside. Use mosquito repellents containing DEET. Be sure to follow the directions on the label.
• Make sure window and door screens are in good shape to prevent mosquitoes from entering the house.
• Remove unnecessary sources of water outside the home that may provide breeding sites for mosquitoes.
• Flush out the water from bird baths and pet dishes often.
• Remove leaf litter, standing water, and debris from roof gutters and boat covers.

For more information on West Nile, visit the CDC's West Nile information page.

Information provided by CDC (Centers for Disease Control and Prevention)