Details of West Nile Virus

West Nile Virus (WN) is a mosquito-borne flavivirus that can cause encephalitis or meningitis in humans and animals. The virus is named after the West Nile region of Uganda where it was first isolated in 1937. The virus appeared for the first time in the United States during a 1999 outbreak in New York that killed seven people. The first case in Canada was confirmed to have been an Ontarian man in September 2002. How do people get infected with West Nile virus? The evidence shows that most people infected with West Nile virus got it from the bite of an infected mosquito. A mosquito becomes infected when it feeds on the blood of a bird that is infected with the virus. About two weeks later, the mosquito becomes capable of passing the virus to people and animals by biting them. There is some evidence that female mosquitoes may be able to transfer WN virus to their offspring, but researchers are still looking into this possibility. In 2002, scientists discovered that people could be infected with West Nile Virus in other ways, including blood transfusions and organ/tissue transplants. The risk of getting WN virus this way is considered to be quite low. There is also evidence that pregnant women can pass the virus to their unborn babies and that the virus may be passed through breast milk. In addition, laboratory workers who handle infected specimens can get WN virus through needle punctures or cuts. It is estimated that fewer than 1% of mosquitoes in any given area are infected with WN virus. This means the risk of being bitten by an infected mosquito is low. However, it could happen to anyone in areas where WN virus is active. The best way to reduce your risk is to avoid getting mosquito bites. What are the symptoms of West Nile virus infection? Most people who are infected with the West Nile virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever: mils symptoms, including: Slight fever Headache Body aches Swollen lymph glands Occasionally a skin rash The symptoms of severe infection (WN encephalitis or meningitis) include: Intense headache High fever Neck stiffness Stupor Disorientation Coma Tremors Convulsions Muscle weakness Paralysis It is estimated that 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. What is the incubation period in humans (i.e. time from infection to onset of disease symptoms) for West Nile encephalitis? Usually 3 to 14 days. How long do symptoms last? Symptoms of mild disease will generally last a few days. Symptoms of severe disease may last several weeks, although neurological effects may be permanent. What treatments are available for people with WN? There is no specific treatment, medication or cure for WN virus. Serious cases are treated with supportive therapies to ease symptoms and prevent secondary infections. These cases may require hospital or nursing care.