Lapis ISSN 2398-2969

West Nile virus infection

Synonym(s): West Nile disease

Contributor(s): Elisabetta Mancinelli, Glen Cousquer


  • CauseWest Nile virus(WNV)    West Nile virus  .
  • Signs: mild non-specific signs seen in clinical cases.
  • Diagnosis: serological conversion, PCR testing of samples for viral RNA.
  • Treatment: none indicated.
  • Prognosis: good.

Presenting signs

  • In rabbits and most other mammals, clinical illness may be accompanied by mild non-specific signs.
  • These include lethargy and reduced appetite.
  • Where neurological signs are seen these may include torticollis/head tilt   Head tilt  , ataxia and incoordination, tremors, hind limb paralysis   Paresis / paralysis: limb  , tetraplegia and loss of righting ability, circling and convulsions.
  • Some rabbits may present with recumbency.
  • Pyrexia is reported in other mammals and may be seen in rabbits.
  • In the horse, neurological signs predominate in clinical cases and may present together with pyrexia.
  • In humans, the main clinical symptoms described are pyrexia, headache, myalgia, arthralgia, fatigue and skin rashes. In severe cases neurological signs may also be seen together with muscle weakness. A lymphadenopathy may be seen in both mild and sever cases but is not always present in severe cases.
  • In birds, sudden death with or without neurological signs are reported. Non-specific respiratory signs may also be reported.

Acute presentation

  • In rabbits, clinical illness is most probably only accompanied by mild non-specific signs.
  • Under experimental conditions, no clinical signs were observed in rabbits following high dose intracerebral injection.
  • Similarly, one study reported no clinical signs (other than a slight increase in temperature, lasting 24 h) following intracerebal inoculation.
  • A single rabbit reportedly demonstrated clinical signs and mortality associated with WNV.

Geographic incidence

  • WNV has been described throughout much of the world, including  Africa, Europe, the Middle East, East and Central Asia and, most recently North America, parts of Central America and the Caribbean.
  • Recent outbreaks of West Nile encephalitis in humans have occurred in Algeria (1994), Romania (1996-2000), the Czech Republic (1997), Congo (1998), Russia (1999-2001), the United States (1999-2009), Canada (19992007), Israel (2000), Southern France (2003), and most recently, in northern Greece (2010).
  • In the Western Hemisphere, most WNV infections have occurred in the United States from 1999-2009.

Age predisposition

  • Not known for rabbits.
  • In humans, most severe cases have been seen in the elderly but all ages are susceptible.
  • In laboratory rodents resistance increases with age and neonates show the greatest susceptibility.

Sex predisposition

  • Not known for rabbits.
  • There are no known sex predispositions reported in other species. One study reported a slightly higher incidence in men compared to women.
  • May be affected by feeding preferences of mosquitoes.

Public health considerations

  • WNV is transmitted to humans by infected mosquitoes.
  • WNV infection in man can lead to one of three outcomes: an asymptomatic infection, a mild febrile syndrome or a neuro-invasive disease called West Nile encephalitis. The reported relative incidence of these three outcomes is 110:30:1.
  • West Nile encephalitis in humans is potentially lethal.
  • Transmission from an infected host, such as a bird or horse, to man has not been demonstrated.
  • There are no records of transmission of WNV from a rabbit to man.

Cost considerations

  • Minimal cost considerations for rabbit owners.
  • In the face of an outbreak of WNV locally, owners may be advised to take steps to protect their rabbits from biting mosquitoes.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Samuel M A & Diamond M S (2006) Pathogenesis of West Nile Virus infection: a balance between virulence, innate and adaptive immunity and viral evasion. J Virol 80 (19), 9349-9360 PubMed.
  • Hayes E B, Komar N, Nasci R S et al (2005) Epidemiology and transmission dynamics of West Nile virus disease. Emerg Infect Dis 11 (8), 1167-1173 PubMed.
  • Tiawsirisup S, Platt K B, Tucker B J et al (2005) Eastern cottontail rabbits (Sylvilagus floridanus) develop West Nile Virus viraemias sufficient for infecting select mosquito species. Vector Borne & Zoonotic Dis (4), 342-350 PubMed.
  • Byrne S N, Halliday G M, Johnston L J et al (2001) Interleukin-1² but not tumor necrosis factor is involved in West Nile virus-induced Langerhans cell migration from the skin in C57BL/6 mice. J Invest Dermatol 117 (3), 702-709 PubMed.
  • Tsai T F, Popovici F, Cernescu C et al (1998) West Nile encephalitis epidemic in southeastern Romania. Lancet 352 (9130), 767-771 PubMed.
  • Goldblum N, Sterk V V & Paderski B (1954) West Nile Fever. The clinical features of the disease and the isolation of West Nile virus from the blood of nine human cases. Am J Hygiene 59 (1), 89-103 PubMed.
  • Bernkopf H, Levine S & Nerson R (1953) Isolation of West Nile virus in Israel. J Inf Dis 93 (3), 207-218 PubMed.
  • Smithburn K C, Hughes T P, Burke A W et al (1940) A neurotropic virus isolated from the blood of a native of Uganda. Am J Tropical Med 20, 471-472 VetMedResource.

Other sources of information

  • Travis D (2008) West Nile Virus in Birds and Mammals. In:  Zoo and Wild Animal Medicine Current Therapy. Volume 6. Eds: Fowler M E & Miller R E. Saunders, St Louis, Missouri, USA.