Clinical Review

West Nile encephalitis

BMJ 2003; 326 doi: (Published 19 April 2003) Cite this as: BMJ 2003;326:865

This article has a correction. Please see:

  1. Tom Solomon, lecturer in neurology and medical microbiology (,
  2. Mong How Ooi, consultant paediatricianb,
  3. David W C Beasley, postdoctoral fellowc,
  4. Macpherson Mallewa, clinical research fellowd
  1. a Departments of Neurological Science and Medical Microbiology, University of Liverpool, Liverpool L9 7LJ
  2. b Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
  3. c WHO Collaborating Center for Tropical Diseases, Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-0609, USA
  4. d Department of Neurological Science, University of Liverpool, Malawi-Liverpool-Wellcome Trust Programme for Tropical Medicine Research
  1. Correspondence to: Tom Solomon
  • Accepted 6 March 2003

Although West Nile encephalitis is yet to spread to the United Kingdom, it is becoming more prevalent in the rest of the world. This article reviews the recent outbreaks and examines the current methods of diagnosis, treatment, and prevention

In the summer of 1999, crows dropping from the New York sky, sick birds at the Bronx zoo, and an unusual cluster of cases of human encephalitis heralded the arrival of West Nile virus in North America.1 Although there were only 62 cases and seven deaths in 1999, the virus has since moved across the continent, and during 2002 there were more than 3500 cases and 200 deaths (see fig A on West Nile virus also occurs in Africa, parts of Asia, and southern Europe, with recent outbreaks in Romania, Russia, and Israel (fig 1).24 Unpublished evidence is reported to show that birds in the British Isles may also have antibody to the virus.5 The recent outbreaks of West Nile virus have drawn attention to the devastating potential of mosquito-borne neurogenic flaviviruses to spread (see box 1 for details).6

Fig 1.

Approximate global distribution of West Nile virus (or its subtype, Kunjin virus)

We reviewed the epidemiology and clinical features of infection with West Nile virus, highlighting the many unanswered questions about how and why such viruses spread and focusing on how to recognise, diagnose, and treat patients with the infection.

Summary points

West Nile encephalitis is caused by West Nile virus, an arthropod-borne virus which is spreading

During 2002 the virus caused more than 3500 cases and 200 deaths in the United States

The virus occurs in Africa, the Middle East, parts of Asia and Australia, and southern Europe, but its presence in Britain has not yet been confirmed

Elderly people and those on immunosuppressive drugs …

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