Skip Navigation Links
Centers for Disease Control and Prevention
nav image
nav image CDC Home Search Health Topics A-Z nav image
West Nile Virus
" "
West Nile Virus Home DVBID Home Search West Nile Virus pages Site Index Contact Us West Nile Virus
  West Nile Virus Basics  
  · Fact Sheet  
  · Q & A  
  Specific Topics  
  · Maps & Human Cases  
  · Clinical Guidance  
  · Lab Guidance  
  · Workplace Safety  
  · Background  
  · Ecology/Virology  
  · Education/Training  
  Resources  
  · In the News  
  · Publications  
  · Conferences  
  · Related Links  
  · State & Local Government Sites
 
  · Guidelines for Surveillance, Prevention, & Control Adobe Acrobat Reader PDF (254 KB/77 pages)  

West Nile Virus Home > Background
Background: Virus History and Distribution

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.

 

 West Nile Virus Map - Click for Larger Image
 

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, Oceania (subtype Kunjin), 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 1999-2001, and France in 2000, and in birds in Israel in 1997-2001 and in the United States in 1999-2002.

In the U.S. since 1999, WNV human, bird, veterinary or mosquito activity have been reported from all states except Hawaii, Alaska, and Oregon.

Human Case and Virus Distribution Information

  • Human case information and maps from 2002
  • From 1999 through 2001, there were 149 cases of West Nile virus human illness in the United States reported to CDC and confirmed, including 18 deaths.


Top of Page


CDC Home | Search CDC | Health Topics A-Z

Page last modified April 6, 2004

Privacy Policy | Accessibility