The West Nile region of Uganda in 1909. ŠAMNH   What is the West Nile virus? It is an infective agent that can cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). What are the symptoms? Most people either have no symptoms or else mild, flu-like ones such as fever, aches, swollen lymph glands, and headache. Occasionally--almost always in elderly patients--the virus can lead to serious illness, causing confusion, high fever, muscle weakness, neurological damage, coma, and even death. But most people who have been infected--over 99%--recover completely. How do you get West Nile virus? The disease is transmitted by the bite of infected mosquitoes (primarily by the species Culex pipiens, the common house mosquito). A mosquito becomes infected when it feeds from a bird that is carrying the virus in its blood. It then spreads the virus in its saliva when it bites a person, another bird, or other animals. There is no documented evidence of direct person-to-person, animal-to-animal, or animal-to-person transmission of West Nile virus. A mosquito is a necessary intermediary. Who is at risk? Anyone who lives in an area where viral activity has been identified has a chance of getting West Nile virus. People over age 50 run the greatest risk of getting seriously ill. Can domestic animals get the virus? The infection rate for dogs and cats is very low. Although they can catch the disease, it tends to be very mild, with the animals recovering completely. Horses seem to be more susceptible to the virus, and in serious cases can develop a form of equine encephalitis and die. But again, the great majority that become infected have mild symptoms and recover completely. Although various species of pet birds might be highly vulnerable to WNV, their chances of getting infected are minimal because they are (typically) confined indoors. If I live somewhere West Nile has been reported and I get a bitten by a mosquito, will I get sick? It's highly unlikely. In areas where the virus has been identified, it is still a very small fraction--less than one percent--of mosquitoes that are actually infected. And even if an infected mosquito does bite you, your chances of getting sick are slim (roughly one in 300), unless you are elderly or your immune system is already compromised. Should I be tested if I get a mosquito bite? Only if you show symptoms. Most mosquitoes aren't infected with WNV, and other mosquito-borne diseases are rare in the New York area. However, you should see a doctor immediately if you develop any severe flu-like symptoms such as high fever, strong headache, or becoming confused or disoriented. Symptoms generally occur between five and fifteen days after being bitten. What percentage of the people who develop West Nile encephalitis die? Between 3% and 15% of those who actually become ill from WNV die. Fatality rates are highest in the elderly. However, since most people infected with WNV rarely even show symptoms and are never hospitalized, the overall death rate due to the virus is considerably less then 1%. Can you get West Nile from another person? No. For example, you can't get the West Nile virus from kissing a person who is infected, or from a health care worker who has treated someone with the disease. Can you get West Nile virus directly from birds? There is no evidence that a person can get the virus from handling infected birds, whether they are alive or dead. However, you should always wear gloves or use double plastic bags when handling any dead animal. Where was West Nile virus first discovered? The virus was first isolated from the blood of a woman in the West Nile district of Uganda in 1937. Subsequently it was found in the blood of patients, birds, and mosquitoes in Egypt in the early 1950s. It was identified as a cause of serious inflammation of the brain and spinal cord in the elderly during a 1957 Israeli outbreak. It was soon recognized as the most widespread of the flaviviruses, a family of viruses that includes St. Louis encephalitis and other diseases with similar symptoms and treatment. Outbreaks have also occurred in Asia, South Africa, parts of Europe, and Australia. How long has West Nile virus been in the United States? Scientists from the Center for Disease Control think the virus has probably been in the eastern U.S.A. since early summer 1999, and possibly longer. It was first detected in New York City in fall 1999--the first time WNV had been discovered anywhere in the Western hemisphere. The 1999 viral outbreak was initially thought to be St. Louis encephalitis, a related disease that is quite common in the central United States. West Nile ultimately claimed the lives of seven people (of 62 believed to have contracted the illness), nine horses (of 25 clinically diagnosed with WNV), and thousands of birds, particularly crows. Scientists and public health officials are working hard to contain a subsequent outbreak.      1 of 3