The History of West Nile Virus

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Introduction

West Nile virus (WNV) has emerged in recent years in temperate regions of Europe and North America, presenting a threat to public and animal health. The most serious manifestation of WNV infection is fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds. WNV has also been a significant cause of human illness in the United States in 2002 and 2003.

 

History

West Nile virus was first isolated from a febrile adult woman in the West Nile District of Uganda in 1937. The ecology was characterized in Egypt in the 1950s. The virus became recognized as a cause of severe human meningitis or encephalitis (inflammation of the spinal cord and brain) in elderly patients during an outbreak in Israel in 1957. Equine disease was first noted in Egypt and France in the early 1960s. WNV first appeared in North America in 1999, with encephalitis reported in humans and horses. The subsequent spread in the United States is an important milestone in the evolving history of this virus.

Geographic Distribution

West Nile virus has been described in Africa, Europe, the Middle East, west and central Asia, and most recently, North America.

Outbreaks of WNV encephalitis in humans have occurred in Algeria in 1994, Romania in 1996-1997, the Czech Republic in 1997, the Democratic Republic of the Congo in 1998, Russia in 1999, the United States in 1999-2003, and Israel in 2000.  Epizootics of disease in horses occurred in Morocco in 1996, Italy in 1998, the United States in 1999-2004, and France in 2000, and in birds in Israel in 1997-2001 and in the United States in 1999-2004.

U.S. Data

From 1999 through 2001, there were 149 human cases of West Nile Virus in the U.S. including 18 deaths. In 2003, there were 9,862 reported human cases and 264 deaths. In the 2004 WNV season there were 2,470 human cases of WNV reported and 88 deaths attributed to the disease. In 2004 the first cases of animal and human WNV were reported. The number of cases in Oregon in 2005 is expected to increase.