West Nile Virus (WNV) has killed thousands of crows and caused human and equine deaths in North America since it first appeared in New York City in 1999. It has been detected in 144 species of birds, 22 species of mosquitoes, as well as in horses, bats, cats, rabbits and other animals. Birds carry the virus and mosquitoes spread it to other birds, animals or humans. Animals, other than horses and birds, rarely show any illness from the infection.
Bagley, Clell V. DVM, "Utah Alert: West Nile Virus" (2003). All Archived Publications. Paper 205.