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Mosquito Information


What is West Nile Virus (WNV)?

The West Nile virus (WNV) is a member of the flavivirus genus which is from the family Flaviviridae. The virus causes a neurological disease that in some cases becomes fatal. WNV is commonly found in Africa, Europe, the Middle East, North America and West Asia. It was introduced to the United States in 1999.

Hosts, Vectors, and Route of Transmission

The original hosts of the virus are birds. When mosquitos feed on birds infected with WNV, they become a vector (they carry the virus but are not affected by it themselves). Vector mosquitos then feed on other animals (commonly horses and humans) and can infect them with WNV. There have been no reports, however, that the virus can be shed from horses or humans onto other organisms, including those within the same species. 

Image of the West Nile virus transmission cycle. The image is divided into two sides with a box in the middle. Inside the box there are images of mosquitoes on the top and birds on the bottom with arrows going from the mosquitoes to the birds and then from the birds to the mosquitoes. Mosquitoes transmit disease and birds are amplifier hosts. There is an arrow going from the mosquitoes to the left side of the image where a horse is in a field outside. The horse is a dead end host. There is also an arrow going from the mosquitoes to the right side of the image where there is a woman planting flowers outside of her house. The woman is also a dead end host.

                                                       Retrieved from the CDC:

Clinical Signs and Prognosis

80% of those infected with WNV will be asymptomatic, however the other 20% do develop West Nile fever or severe disease. Additional signs associated with the fever are headaches, body aches, lethargy, and vomiting. About 1 in 150 people infected with WNV will develop a more severe form of the disease, which could present as West Nile encephalitis or meningitis or West Nile poliomyelitis. Signs of these conditions include headache, high fever, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. There is no distinct treatment other than supportive care, and it does occasionally result in fatalities. 


Centers for Disease Control and Prevention (2015, February 12). Transmission. Retrieved from

World Health Organization (2011, July). West Nile virus. Retrieved from