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West Nile Virus (WNV) is a mosquito-borne virus which can cause West Nile encephalitis (inflammation of the brain). Although this virus is commonly found in Africa, West Asia and the Middle East, it is believed that the virus appeared in the eastern United States sometime in the summer of 1999. It is closely related to the St. Louis encephalitis virus commonly found in the southeastern and mid-western U.S., and only rarely in the northeast.
Prior to August of 1999, WNV had never been reported in the U.S. In 1999, 62 cases of the severe disease occurred in the New York City area, resulting in 7 deaths.
Because of this recent outbreak, public health and mosquito control professionals have heightened surveillance efforts to determine the most effective methods of mosquito control.
WNV is transmitted through the bite of an infected mosquito, primarily a species called 'Culex pipiens'. This type of mosquito is most often found in urban and suburban communities, and is commonly referred to as the 'northern house mosquito.'
West Nile Virus appears to circulate in wild bird populations.
When a mosquito feeds on an infected bird, it becomes capable of transmitting the WNV to humans and animals while biting to take its next blood meal.
The virus is injected into the host, where it may then multiply and cause illness. Infected mosquitoes were the cause of the recent outbreak in the New York City area.
WNV is not transmitted from person-to-person, nor is there evidence indicating transmission from an infected bird to humans.
The virus has an incubation period of 5 to 15 days. Most infections are mild and can result in flu-like symptoms such as fever, headache and body aches. Swollen lymph glands may also develop, and in approximately one-half of the cases, a skin rash may occur, spreading from the trunk of the body to the extremities and the head. A more severe infection can be marked by high fever, neck stiffness, stupor, disorientation, tremor, muscle weakness, and rarely, death. The virus interferes with normal central nervous system functioning and causes inflammation and swelling of the brain tissue.
Anyone residing in an area where the virus has been identified is at risk of getting an infection. Those older than 50 years of age have the highest risk for severe disease. The case-fatality rate is highest in the elderly or those with compromised immune systems.
There is no specific treatment for WNV, nor is there a vaccine. In severe cases, intensive supportive therapy is needed, including hospitalization, intravenous fluids and nutrition, airway management, prevention of secondary infections and good nursing care.
It appears that most birds do not normally show signs of infection with WNV. They do however, serve as natural reservoirs of the virus, and can pass the virus to feeding mosquitoes. During the New York area outbreak however, there was a large die-off of American crows. This was seen in many counties in New Jersey, and as far west as Hunterdon County, where two infected crows were identified. Other species of birds, including red tail hawks and blue jays, have been reported to show signs of Illness ranging from encephalitis to death.
Domestic animals such as dogs and cats do not appear to be at special risk of infection however, the virus was isolated from one feral cat in Union County, NJ. It is possible that pets could become infected by eating dead infected birds, but this is still unproven. Infected animals should receive standard veterinary care. Full recovery from the infection is likely.
Data suggest that while horses are susceptible to WNV, most will recover from the infection. However, federal investigations determined that WNV was responsible for several deaths of horses on Long Island in 1999. Horses become infected in the same way humans do, from the bite of an infected mosquito. There is no evidence of 'horse-to-horse' or 'horse-to-person' transmission of the WNV. Vaccines for other types of equine encephalitis are most likely not effective against WNV.
Most importantly, it is essential that all homeowners take action to reduce mosquito breeding areas on private property. Effective mosquito control - on a county-wide basis - depends on each resident doing his or her part.
Mosquito breeding around the home can be greatly reduced by following a few simple guidelines. Note that mosquitoes will lay eggs in any container holding water rich in decomposing material (like leaves, grass clippings, etc.) Review this list often!