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.