WNV is transmitted through the bite of an infected mosquito, primarily a species called 'Culex pipiens'. 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.
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.