Dogs and cats have been known to become infected. Although West Nile Virus doesn't appear to cause extensive illness in dogs or cats, there has been one case in Botswana in 1982 of a dog dieing from West Nile Virus. As well, virus was isolated from several dead cats in 1999 and 2000, and the Center for Disease Control did a serosurvey of dogs and cats within the area which showed a low infection rate. It is unknown how long the infection lasts in dogs and cats. The human infection is usually not fatal, however it is a serious threat to older individuals and those with compromised immune systems.
Most human infections are actually quite mild with a fever, headache, and body aches.
Occassionally, humans develop a skin rash and swollen lymph nodes. If an individual develops a severe form of the disease, they will have a severe headache accompanied by a high fever, neck stiffness, dissorientation, stupor, coma, tremors, convulsions, muscle weakness, paralysis, and rarely, death. The incubation period in humans is about 3-15 days and the disease progresses over two to three weeks. The U.S. infection had 62 severe cases, and 7 deaths. In 2000, these numbers have dropped to 17 cases with only one death.