History of Virus - Transmission & Infection - Effects of WNV - Prevention - More Information  

West Nile Virus has emerged in recent years throughout the temporate zones of Europe and North America. Causing a variety of conditions in its hosts, the most serious manifestation of WN virus infection is fatal encephalitis (inflammation of the brain) in humans and horses, and many birds.

While many forms of encephalitis exist, West Nile Virus was first isolated and identified in the West Nile District of Uganda in 1937. The virus, which was seemingly isolated to North Eastern Africa, became recognized as a cause of severe human meningoencephalitis (inflammation of the spinal cord and brain) in elderly patients during an outbreak in Israel in 1957. In addition to the human victims of this disease, the virus was found Egypt and France during 1960s to have fatal effects within horses. While this disease spread through Northern African and Southern Europe, 1999 marked the first appearance of West Nile Virus in North America, with encephalitis reported in both humans and horses.

West Nile in the United States
The West Nile Virus first came to the U.S. public's attention following an outbreak in New York in August 1999 where eight patients has contracted ecephalitis from the virus. In the following four years the virus spread to almost all 48 contiguous states. In the United States cases were initially infrequent until 2002, when a massive outbreak occurred in the Mississippi River basin during August and September. As it has spread through the country, nearly 8,500 people have been diagnosed with the virus, which has lead to 189 deaths. The emergence of the new disease has been followed closely by the media and the government. Many areas that have experienced significant outbreaks of the Virus have occured have implemented surveillance and control programs to hopefully curb the effects of this virus.

Map of the Spread of West Nile Virus from 1999-2002
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What Exactly is West Nile Virus?

  • Family: Flaviviridae
  • Genus: Flavivirus Japanese Encephalitis Antigenic Complex
  • Complex includes: Alfuy, Cacipacore, Japanese encephalitis, Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis, Rocio, Stratford, Usutu, West Nile, and Yaounde viruses.
  • Flaviviruses: share a common size (40-60nm), symmetry (enveloped, icosahedral nucleocapsid), nucleic acid (positive-sense, single stranded RNA approximately 10,000-11,000 bases), and appearance in the electron microscope. Therefore, images of West Nile virus are representative for this group of viruses.
Map of West Nile Virus in 2003
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