Frequently Asked Questions About West Nile Virus

Questions and answers about West Nile virus, provided by the Centers for Disease Control and Prevention.

Q: What is West Nile encephalitis?

A: It is an infection of the brain caused by the virus. Encephalitis means an inflammation of the brain and can be caused by viruses and bacteria, including viruses transmitted by mosquitoes.

Q: Where did the virus come from?

A: It has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia and the Middle East. It was first reported in the United States in 1999.

Q: How many cases of the virus in humans have occurred in the United States?

A: There have been 445 cases and 32 deaths in this country and most of those have occurred in 2002. So far this year, 296 cases and 14 deaths have been reported, with 211 cases and 11 deaths in Louisiana and Mississippi alone.

Q: How do people get the virus?

A: People become infected by the bite of a mosquitoes infected with the virus. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then transmit the virus to humans and animals while biting to take blood.

Q: If I live in an area where birds or mosquitoes with the virus have been reported and a mosquito bites me, am I likely to get sick?

A: No. Even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Even if the mosquito is infected, less than 1 percent of people who get bitten and become infected will get severely ill. The chances of a person becoming severely ill from any one mosquito bite are extremely small.

Q: Can you get the virus from another person?

A: No. It is not transmitted from person-to-person. For example, you cannot get the virus from touching or kissing a person who has the disease, or from a health-care worker who has treated someone with the disease.

Q: Is a woman's pregnancy at risk if she gets the virus?

A: There is no documented evidence that a pregnancy is at risk due to infection with the virus.

Q: Besides mosquitoes, can you get the virus directly from other insects or ticks?

A: Infected mosquitoes are the primary source for the virus. Although ticks infected with the virus have been found in Asia and Africa, there is no information to suggest that ticks play any role in the U.S. cases.

Q: How many types of animals have been found to be infected with the virus?

A: Although the vast majority of infections have been identified in birds, the virus has been shown to infect horses, cats, bats, chipmunks, skunks, squirrels and domestic rabbits.

Q: Can you get the virus directly from birds or other infected birds or animals?

A: There is no documented evidence of animal-to-person transmission of the virus. Normal veterinary infection control precautions should be followed when caring for an animal suspected to have any viral infection.

Q: How does the virus cause severe illness and death in humans?

A: Following transmission by an infected mosquito, the 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 tissue.

Q: What proportion of people with severe illness due to the virus die?

A: Among those with severe illness due to the virus, fatality rates range from 3 percent to 15 percent and are highest among the elderly. Less than 1 percent of those infected with the virus will develop severe illness.

Q: What can I do to reduce my risk of becoming infected with the virus?

A: Apply insect repellent sparingly to exposed skin. The more "DEET" a repellent contains the longer time it can protect you from mosquito bites. When possible, wear long-sleeved shirts and long pants whenever you are outdoors. Place mosquito netting over infant carriers when you are outdoors with infants. Consider staying indoors at dawn, dusk, and in the early evening, which are peak mosquito-biting times. To avoid helping mosquitoes breed in your environment, drain standing water. Routinely empty water from flower pots, pet bowls, clogged rain gutters, swimming pool covers, discarded tires, buckets, barrels, cans, and other items that collect water where mosquitoes can lay eggs.

Q: None of the products in the store says "DEET."

A: Most insect repellents that are available in stores are labeled with the chemical name for "DEET." Look for N,N-diethyl-m-toluamide or, sometimes, N,N-diethyl-3-methylbenzamide.

Q: Is there a vaccine against the virus?

A: No, but several companies are working toward developing a vaccine. carried out.

Q: Who is at risk for getting the virus?

A. All residents of areas where virus activity has been identified are at risk of getting the virus; persons over 50 years of age have the highest risk of severe disease.

Q: What are the symptoms of infection?

A: Most infections are mild, and symptoms include fever, headache and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis and, rarely, death.

Q: What is the period between infection and when symptoms may appear?

A: Usually three to 15 days.

Q: How long do symptoms last?

A: Symptoms of mild disease will generally last a few days. Symptoms of severe disease may last several weeks, although neurological effects may be permanent.

Q: How is the virus treated?

A. There is no specific therapy. In more severe cases, treatment may involve hospitalization, intravenous fluids, help with breathing, prevention of secondary infections and good nursing care.

Q: What is the treatment for an animal infected with the virus?

A: There is no reason to destroy an animal just because it has been infected. Full recovery from the infection is likely and veterinarians use standard practices for treating animals infected with a virus.

Q: My horse is vaccinated against other forms of encephalitis. Will these vaccines protect this virus?

A: No. There is no cross-protection.

Q: Can I vaccinate my horse against infection?

A: A vaccine for horses was recently approved, but its effectiveness is unknown.