This disease was first described in Australian cockatoos in the early 1970's. Since that time, the disease has infected over 50 different species of birds. The virus causing the disease works slowly. The disease is often called "Bird AIDS" due to some similarities between it and the human disease of AIDS.
The West Nile Virus (WNV) is transmitted by the bite of a mosquito (primarily Culex species) that is infected with the virus. The mosquitoes become infected after biting birds carrying the West Nile Virus.