West Nile

From GreenWiki

West Nile is a virus which recently arrived in the United States in 2002. It is harbored in bird populations and transmitted to humans when mosquito populations get of one specific type of mosquito, culex pipiens, gets very high when birds of certain types also have the virus.

West Nile is very rare. Healthy people usually experience a mild form of it, but very rarely, a very serious form may cause very serious health effects and extremely rarely, some cases have been fatal. Those with weakened immune systems are most at risk.