ISSN 2398-2942      

West Nile fever virus

icanis

Synonym(s): WNV, WNF


Introduction

Classification

Taxonomy

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

Etymology

  • Latin: flavus - yellow.

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Clinical Effects

Epidemiology

Habitat

  • 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.

Lifecycle

  • 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.

Transmission

  • 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

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.

Diagnosis

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Further Reading

Publications

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.

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