Bovis ISSN 2398-2993

Rift valley fever

Synonym(s): Enzootic Hepatitis, Afrik

Contributor(s): Mike Reynolds , James Wood

Introduction

  • Cause: Rift Valley Fever virus is a single stranded RNA virus of the family Bunyaviridae within the genus Phlebovirus.
  • Signs: see below.
  • Diagnosis: microscopy, RT-PCR and/or Virus neutralization antibody test Elisa.
  • Treatment: none.
  • Prognosis: poor, particularly in calves and young animals but varies according to species and clinical presentation.

Pathogenesis

Etiology

  • As in most vector borne diseases, peak incidence is seen during the wet season, when vector numbers proliferate.
  •  A range of vector species are capable of disease transmission and include mosquito species such as Aedes, Culex and Anopheles.
  •  Mechanical transmission by other vectors such as midge, sand flies, black flies and stable flies may also occur Cattle flies and larvae: overview.

Predisposing factors

General

  • Disease outbreaks are often associated with periods of heavy rainfall in Southern and East Africa and may be associated with irrigation projects in drier regions. Reduced rain fall during periods of El Nino leads to a greater need for irrigation projects and may support disease outbreaks.
  • Increased vector loads during the wet season, particularly after a period of low rainfall and the creation of a large naïve population.

Pathophysiology

  • Hepatocytes are the primary site of viral replication.
  • Lesions may include hepatocellular necrosis which may be local or diffuse.
  • A severe leukopenia is a common finding.

Timecourse

  • Incubation is 12- 24 hours in calves and 24-72 hours in adult animals with a duration of 10-20 days.

Epidemiology

  • 5-25 year cycles produce populations of naïve animals.
  • The virus can pass transovarially in certain Aedes species meaning large epizootic outbreaks can occur in previous drought regions following rainfall, when vast numbers of infected Aedes mosquito’s emerge. 

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

Other sources of information

  • OIE technical disease card (2009) Rift Valley Fever.  pp 1-5.  Accessed 20/02/2017.
  • Brown C & Torres A (2008) USAHA Foreign Animal Diseases. Seventh Edition.
    Committee of Foreign and Emerging Diseases of the US Animal Health Association. Boca
    Publications Group, Inc. Canada, pp 369-377.
  • Radostits O M, Gay C C, Blood D C, Hinchcliff  KW (2005) Diseases caused by viruses and Chlamydia. In: Veterinary Medicine, 9th edition. W.B. Saunders, Philadelphia, pp 1042-1043.


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