Viruses Genomes - WEST NILE VIRUS

West Nile virus (WNV) is an infection that mainly affects birds, but it can be passed to humans through an infected mosquito's bite.

WNV was first discovered in a woman from the West Nile District of Uganda in 1937. WNV then spread across areas of Africa. WNV was first detected in the Western Hemisphere in 1999 and has since rapidly spread across the North American continent. In addition, WNV activity has been detected in Puerto Rico, the Dominican Republic, Jamaica, Guadeloupe and El Salvador and recently cases were reported in Ireland.

The virus is transmitted by the bite of an infected mosquito. WNV is maintained in nature when an arthropod vector transmits the virus between vertebrate hosts. The primary vector for WNV in the United States is the Culex pipiens mosquito that commonly breeds in urban areas and prefers to feed on birds. At least 43 mosquito species in the U.S., including other Culex, Aedes, Anopheles, and Psorophora mosquito species, have tested positive for WNV. Mosquitoes acquire WNV when feeding on infected birds. The virus is then stored in the mosquito's salivary glands and transmitted to humans and other incidental hosts when the mosquito takes a blood meal. The virus has been detected in many wild bird species, including the American crow. Humans, horses, and most other mammals are generally considered incidental or dead-end hosts, as they are not known to develop a high enough viral load to either transmit, or become a reservoir for WNV.

Symptoms from infection generally appear within 2-14 days after the bite. Most people who are infected by the the virus experience no symptoms or mild, flu-like symptoms. Those at higher risk of developing potentially serious conditions are the elderly and those with lowered immune systems.

There is no specific treatment for West Nile virus and the only protection is to try and avoid mosquito bites. Studies show that many people with severe West Nile Virus infection suffered lingering and debilitating symptoms well after they left the hospital, the virus killed 264 in the US last year however morbidity is more significant for elderly patients.

References:

http://www.cdc.gov/ncidod/dvbid/westnile/
http://westnilevirus.nbii.gov/
http://www.bbc.co.uk/health/conditions/westnile1.shtml
http://www.fda.gov/oc/opacom/hottopics/westnile.html
http://www.odh.state.oh.us/odhprograms/zoodis/wnv/wnv1.htm