ISSN 2398-2977      

Getah virus

pequis

Synonym(s): Arbovirus


Introduction

Classification

Taxonomy

  • Family: Togaviridae.
  • Genus:Alphavirus.
  • A Semliki Forest virus: included in the Semliki Forest antigenic complex areChikungunyavirus,Onyong-nyong Mayarovirus and Una-Semliki Forestvirus.
  • Getahvirus has three recognized subtypes:
    • Ross River.
    • Bebaru.
    • Sagiyama.

Distribution

  • While isolated from mosquitoes of various species in Australia, Cambodia, China, Japan, Malaysia, the Philippines, Russia, Siberia, Sri Lanka and Thailand, geographic distribution of virus likely more widespread.
  • It was first isolated from horses in Japan and is also commonly found in pigs in Asia.

Active Forms

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Clinical Effects

Epidemiology

Habitat

  • Culexspp andAldesspp mosquitoes primary vectors of the virus.
  • The pig is the most significant vertebrate host because it is kept in large numbers in virus endemic regions of the world and develops a viremia of significant magnitude and duration for it to act as an amplifying host of the virus.
  • Antibodies have been found in many species, including healthy humans and horses. It has been suggested that cattle, chickens and wild birds may possibly play a role in maintenance and transmission.

Lifecycle

  • Getah virus is responsible for infrequent widespread outbreaks of disease in horses, particularly among racehorses in Japan.
  • Pigs are thought to be the reservoir for infection of mosquitoes and act as amplifiers of the virus. They develop a high titered viremia. The virus is only mildly pathogenic in pigs, causing occasional reproductive problems, including abortion and neonatal mortality.
  • The virus is likely maintained in tropical regions of Asia by year-round cycling between pigs and mosquitoes.
  • The mechanism of persistence in temperate regions is unclear, but may involve overwintering of infected mosquitoes, or possibly transovarial transmission in the vector. Alternatively, the virus may be reintroduced.

Transmission

  • Transmission between horses is mainly by mosquitoes, but spread through direct or indirect contact with nasal secretions may also occur.
  • The morbidity rate reported in one outbreak was roughly 40%.
  • There is evidence of congenital transmission of the virus in pigs.

Immunological effects

  • Initial humoral response comprises a mixed population of group-specific, complex-specific and type-specific antibodies.
  • Neutralizing antibodies develop within 2 weeks and are the most type-specific antibodies.
  • IgM antibodies formed as an initial response to infection are complex-specific, cannot be used for a definitive diagnosis, however, they do indicate recent infection with the virus.
  • An IgG antibody response develops later and may persist for the life of the horse.

Pathological effects

  • Fever, urticarial rash consisting of scattered macules confined to the dermis, serous nasal discharge, submaxillary lymphadenopathy, and hindlimb edema in horses. Accompanied by mild lymphopenia and monocytosis. Moderate lymph node enlargement. Most affected horses recover fully in 12 weeks   Getah virus disease  .
  • Occasionally associated with reproductive disorders (abortion, stillbirth and fetal abnormalities) pigs.

Control

Control via animal

  • Surveillence, involving clinical observation and serological testing, is carried out early in the vector season (the summer in Japan).

Control via chemotherapies

  • Larvicides are used to control mosquito breeding.
  • Insecticidal space sprays are used to kill adult mosquitoes and thus reduce risk of virus transmission in the face of a potential outbreak.

Control via environment

  • Widespread disease occurrences are prevented and controlled by reducing vector populations through an integrated pest-management program.
  • Mosquito breeding is controlled by elimination of breeding sites and using larvicidal agents.

Vaccination

  • Use of an inactivated vaccine has been reported in racing Thoroughbreds in Japan.
  • Field and experimental findings indicate vaccination protects against disease and viremia.
  • Annual revaccination is recommended.

Other countermeasures

  • Designated a restricted pathogen in the United States and other countries in which it is exotic.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Fukunaga Y, Kumanomido T & Kamada M (2000) Getah virus as an equine pathogen. Vet Clin N Am Eqine Pract 16 (3), 605617 PubMed.
  • Kamada M, Kumanomido T, Wada R et al (1991) Intranasal infection of Getah virus in experimental horses. J Vet Med Sci 53, 855858 PubMed.
  • Kamada M, Wada R, Kumanomido T et al (1991) Effect of viral inoculation size on appearance of clinical signs in equine Getah virus infection. J Vet Med Sci 53, 803806 PubMed.
  • Shibata I, Hatano Y, Nishimura M, Suzuki G & Inaba Y (1991) Isolation of Getah virus from dead fetuses extracted from a naturally infected sow in Japan. Vet Microbiol 27, 385391 PubMed.
  • Morita K & Igarashi A (1984) Oligonucleotide finerprinting analysis of strains of Getah virus isolated in Japan and Malaysia. J Gen Virol 65, 18991908 PubMed.
  • Fukunaga Y, Ando Y, Kamada M et al (1981) An outbreak of Getah virus infection in horses clinical and epizootic aspects at the Miho Training Center in 1978. Bull Eq Res Inst (Japan) 18, 94102.
  • Imigawa H, Ando Y, Kamada M et al (1981)Sero-epidemiological survey on Getah virus infection in light horses in Japan. Jpn J Vet Sci 43, 797802.
  • Akiyama Y (1980) Getah virus infection among horses. J Jpn Vet Med Assoc 33, 567581.
  • Kamada M, Ando Y, Fukunaga Y et al (1980) Equine Getah virus infection: isolation of the virus from racehorses during an enzootic in Japan. Am J Trop Med Hyg 29, 984988 PubMed.
  • Sentsui H & Kono Y (1980) An epidemic of Getah virus infection among racehorses: isolation of the virus. Res Vet Sci 29, 157161.

Other sources of information

  • Timoney P J (2004) Getah Virus Infection. In: Infectious diseases of Livestock with Special Reference to South Africa. Ed: Caetzer E. 2nd Edition, Oxford University Press. pp 1023-1026. ISBN: 01957820E.
  • Calisher C H & Walton T E (1996) Getah Virus Infections. In: Virus Infections of Vertebrates. Vol 6; Infections of Equines. Ed: Studdert M J. Elsevier. pp 356. ISBN 0444825274.

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