ISSN 2398-2942      

West Nile fever virus


Synonym(s): WNV, WNF




  • Family: Flaviviridae.
  • Genus: Flavivirus.
  • Group: Japanese Encephalitis.


  • Latin: flavus - yellow.

Active Forms

This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Clinical Effects



  • High level viremia occurs in birds.
  • Many species of mosquitoes have been shown to be adequate hosts.
  • Virus has also been isolated from ticks; their role in transmission is not clear; transtadial transmission may be important for virus maintenance.
  • Overwintering mechanism not known.


  • Virus circulates primarily between mosquitoes and birds.
  • Inoculation into incidental host results in transient viremia followed by infection of CNS.
  • Infection of CNS is enhanced by other factors that compromise the blood-brain barrier.
  • Replication occurs in the cellular cytoplasm.


  • Arthropod-borne transmission.
  • Peak of incidence in summer.
  • Dogs and cats infected when bitten by infected mosquito.
  • Virus can also be transmitted via contact with infected animals, their blood, or other tissues - although this form of transmission is extremely rare.

Pathological effects

  • Neuronal and glial infection lead to destruction due to direct viral injury.
  • Inflammation also leads to neuronal and astrocyte destruction.
  • Dysfunction of neurons without cell death may occur.
  • Subclinical infection or mild febrile disease may result in lieu of encephalitis.
  • Most (80%) human infections appear to be asymptomatic. Neurologic disease is more likely to develop in older people.

Other Host Effects

  • Humans, dogs and horses are incidental hosts, and not a source of virus spread.
  • Pathogenicity and virulence may be strain-related.
  • There is no specific treatment for WNV infection.
  • Full recovery likely.


Control via environment

  • Mosquito and tick control, eg permethrins Permethrin.
  • There are few commercial products safe to use on cats.
  • Minimize time pet spends outdoors at dawn, dusk and evening, when mosquitoes are most active.


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hayes E B & Gubler D J (2006) West Nile Virus: epidemiology and clinical features of an emerging epidemic in the United States. Annu Rev Med 57181-194 PubMed.
  • Karaca K, Bowen R, Austgen L E et al (2005) Recombinant canarypox vectored West Nile virus (WNV) vaccine protects dogs and cats against a mosquito WNV challenge. Vaccine 23 (29), 3808-3813 PubMed.
  • Kile J C, Panella N A, Komar N et al (2005) Serologic survey of cats and dogs during an epidemic of West Nile virus infection in humans. JAVMA 226 (8), 1349-1353 PubMed.
  • Read R W, Rodriguez D B & Summers BA (2005) West Nile virus encephalitis in a dog. Vet Pathol 42 (2), 219-222 PubMed.
  • Austgen L E, Bowen R A, Bunning M L et al (2004) Experimental infection of cats and dogs with West Nile virus. Emerg Infect Dis 10 (1), 82-86 PubMed.
  • Ebel G D, Carricaburu J, Young D et al (2004) Genetic and phenotypic variation of West Nile virus in New York, 2000-2003. Am J Trop Med Hyg 71 (4), 493-500 PubMed.
  • Buckweitz S, Kleiboeker S, Marioni K et al (2003) Serological, reverse transcriptase-plymerase chain reaction, immunohistochemical detection of West Nile virus in a clinically affected dog. J Vet Diagn Invest 15 (4), 324-329 PubMed.
  • Rappole J H & Hubálek Z (2003) Migratory birds and West Nile virus. J Appl Microbiol 94 (Suppl), 47S-58S PubMed.
  • Komar N, Panella N A & Boyce E (2001) Exposure of domestic animals to West Nile virus during an outbreak of human encephalitis, New York City, 1999. Emerg Infect Dis (4), 736-738 PubMed.
  • Kramer L D & Bernard K A (2001) West Nile virus infection in birds and mammals. Ann N Y Acad Sci 951, 84-93 PubMed.
  • Kulasekera V L, Kramer L, Nasci R S et al (2001) West Nile virus infection in mosquitoes, birds, horses and humans, Staten Island, New York, 2000. Emerg Infect Dis (4), 722-725 PubMed.
  • Marfin A A & Gubler D J (2001) West Nile encephalitis: an emerging disease in the United States. Clin Infect Dis 33 (10), 1713-1719 PubMed.
  • Ostlund E N, Crom R L, Pedersen D D et al (2001) Equine West Nile encephalitis, United States. Emerg Infect Dis (4), 665-669 PubMed.
  • Nolen R S (2000) West Nile virus survives winter; no surprise, says CDC. JAVMA 216 (8), 1199-1200 PubMed.
  • Rappole J H, Derrickson S R & Hubálek Z (2000) Migratory birds and spread of West Nile virus in the Western Hemisphere. Emerg Infect Dis (4), 319-328 PubMed.
  • Blackburn N K, Reyers F, Berry W L et al (1989) Susceptibility of dogs to West Nile virus: a survey and pathogenicity trial. J Comp Pathol 100 (1), 59-66 PubMed.
  • Johnson B K, Chanas A C, Shockley P et al (1977) Arbovirus isolations from, and serological studies on, wild, and domestic vertebrates from Kano Plain, Kenya. Trans Roy Soc Trop Med Hyg 71 (6), 512-517 PubMed.
  • Sixl W, Batiková M, Stünzner D et al (1973) Haemagglutination-inhibiting antibodies against arboviruses in animal sera, collected in some regions in Austria. II. Zentralbl Bakteriol Orig A​ 224 (3), 303-308 PubMed.
  • Topciu V, Roşiu N, Arcan P et al (1971) Contributions to the study of arboviruses in Banat. Rev Roum Inframicriobiol (2), 101-106 PubMed.

Other sources of information

  • Hannoun C et al (1969) Epidemiology of West Nile infections in the South of France. In: Bardos Vet al Arboviruses of the California Complex and the Bunyamwera Group. pp 379-387. Vzdavatelstvo Slov. Akad. Vied, Bratislava.





Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field