West Nile Virus Infection West Nile Fever, West Nile Neuroinvasive Disease, West Nile Disease, Near Eastern Equine Encephalitis, Lordige

West Nile virus (WNV) is an avian virus that can cause fatal disease in some species of mammals, reptiles and birds. Most clinical cases occur in humans and horses. Approximately 80% of infected humans remain asymptomatic; 20% have flulike symptoms. Less than 1% develop meningitis, encephalitis or acute paralysis, but some of these cases are fatal or result in permanent impairment. Neurological signs are also seen in some infected equids, and occasionally in other mammals. Outbreaks have been reported in alligators. Some newer isolates of West Nile virus seem to be particularly virulent. Before 1994, disease occurred only sporadically in humans and horses, or as relatively small epidemics in rural areas, and severe neurological signs were uncommon in most outbreaks. Until 1999, West Nile virus was also confined to the Eastern Hemisphere. However, severe outbreaks were reported in Algeria, Romania, Morocco, Tunisia, Italy, Russia and Israel between 1994 and 1999, and West Nile virus spread to North America in 1999. An increased incidence of neurological disease and a higher case fatality rate have been associated with these viruses. Some recent viral isolates also cause clinical signs in birds. Consequently, West Nile fever has emerged as a significant human and veterinary health concern in the Americas, Europe, the Mediterranean basin and other areas. The effects of West Nile virus have been particularly dramatic in North America, where widespread epidemics have occurred in horses and humans. Although vaccination can control the disease in equids, no human vaccine is available, and thousands of people become ill in the U.S. and Canada each year. Many North American species of birds have also been affected by this virus. It has killed large numbers of crows, blue jays and other corvids, as well as American robins, house wrens, eastern bluebirds, tufted titmice, chickadees and sage grouse. Outbreaks have been reported in domesticated geese, pheasants and partridges, and occasional cases occur in captive psittacine birds. Many species of zoo birds have been affected. The effects of this virus on threatened or endangered species could be significant. California condors and greater sage grouse, which are both susceptible to this virus, are of particular concern. The West Nile virus found in the U.S. has become established in Canada, parts of Central and South America and the Caribbean, and it is continuing to spread. If this virus were introduced into Hawaii, it could be disastrous for some native birds.