West Nile Virus Encephalitis and Myocarditis in Wolf and Dog

S its 1999 introduction in New York, West Nile virus (WNV) has spread to >40 states, causing seasonal mosquito-borne disease in humans, horses, and birds (1–7). We recently identified two Illinois canids (a captive wolf and a domestic dog) with severe disease associated with WNV infection. Outside the Western Hemisphere, WNV has been endemic for decades (4,8–11). Canids have not been thought to be important in the epidemiology of this virus. However, a dog with neurologic disease that died in Africa in 1977 is now thought to have been infected with WNV (9,12). In a recent study in which four dogs were experimentally infected, no clinical disease was observed, and a low viremia developed in one dog (11). Natural infections occur in dogs, as indicated by serum antibodies; seropositivity in surveys was 37% in the 1980s in South Africa, 24% in the 1990s in India, and 5% in 1999 in New York City (10,11,13). In addition, a few individuals of some mammalian species have been listed as infected (not diseased): 14 bats, four rodents, three rabbits, two cats, two raccoons, and a skunk (6).