West Nile virus

The evolution of West Nile virus (WNV) has resulted in the emergence of WNV variants that have a significant pathogenicity for humans, horses, and birds. WNV appeared in North America in New York City in 1999 and has since spread throughout the continent into the Caribbean and Mexico and is now believed to be enzootic in much of the United States and southern Canada. Crows, the blue jay, chickadees, hawks, and owls appear to be the most susceptible to WNV disease, although mortality has been reported in nearly 200 species of birds. Disease in companion birds is rare. WNV disease in birds is rapidly fatal and signs, if they occur, are predominately of the central nervous system. Characteristic necropsy findings in birds are intraosseous hemorrhage of the calvaria, an encephalitis, myocarditis, and pancreatitis. Infection can be confirmed by PCR, antigen detection, and virus isolation. Chickens and turkeys are refractory to WNV disease, and chickens have been used to monitor WNV activity. Domestic geese appear to be relatively susceptible to WNV disease. Outbreaks of WNV in Europe, Israel, and the United States have resulted in a significant number of cases of meningitis, encephalitis, and acute flaccid paralysis in people. Encephalitis has also been a common sequella to WNV infection in horses in Europe, North America, and Africa. WNV disease occurs sporadically in many other species of mammals and has been reported to cause significant mortality in a commercial operation of alligators.