smission patterns.Epidemics of WN occurred in the Rhone delta region of France in 1962, 1963, and 1964. The largest epidemic of WN, involving thousands of clinical cases, was reported in South Africa in 1974. Epidemic activity was again reported in South Africa in 1983 and 1984. Human cases were reported in southeast Romania in 1996 and 1997. Most recently, WN virus(es) was apparently introduced into the northeastern region of the borough of Queens in NYC during the summer of 1999.West Nile is more mobile than other closely related viruses like the SLE viruses in North America and MVE viruses in Australia. West Nile viruses have spread from Africa to Western Europe, the Middle East, Eastern Europe, and now North America. To date, close relatives of WN like SLE and MVE have remained confined to their home regions.THE DISEASE In humans, infection with WN can cause clinical or subclincal symptoms. Clinical symptoms vary from temporary fever to serious encephalitis. The disease can be severe in the elderly, but is usually mild in healthy adults and children. The incubation period for WN is 3-6 days. Onset of disease symptoms is usually sudden, beginning with a sustained, elevated fever. Clinical infection can include severe headache; a rash, usually on the trunk; and swollen lymph nodes. Symptoms of WN infection can also include eye, muscular and back pains, and gastrointestinal problems. In severe cases, there are often symptoms of encephalitis with eventual neurological involvement and sometimes death. Humans experience a low-level viremia that lasts about 6 days. Mortality rates in humans range from 5 to 13%.In domestic animals, clinical signs of WN infection have only been observed in horses, even though most horse infections are asymptomatic. However, in the WN epidemic in France during 1962-64, horses experienced 25% mortality. As with horses, cattle, sheep, and camels can also be infected with WN, but clinical symptoms and viremia ca...
