Getah Virus: Significance as an Equine Pathogen

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An outbreak of illness at a Japanese racing stable in the latter half of 2014 re-awakened awareness of Getah virus and its potential as an equine pathogen. The first indication that the virus could cause illness in horses was the widespread occurrence of a disease syndrome among racehorses at two training centers in Japan in 1978. Subsequently, the virus was implicated in a clinically similar disease outbreak on a Thoroughbred breeding farm in India during 1990.

Getah virus is a mosquito-borne arbovirus that is a member of the genus Alphavirus, family Togaviridae. First isolated from mosquito pools collected in Sarawak (Malaysia) between 1968 and 1970, Getah or one of its antigenically related viruses, can be found over a wide geographic range extending from Eurasia to Australia. Results of serologic surveys have confirmed infection in humans and a wide diversity of domestic and wildlife animal species wherever the virus is present. Serologic evidence of Getah virus activity in horses in Japan can be traced back to 1961. Subsequent studies have shown that the infection was widespread in equine populations throughout that country. Notwithstanding this fact, however, disease events caused by Getah virus have been very infrequent.

Naturally occurring disease caused by Getah virus has only been reported in horses and in swine. While the vast majority of primary infections in horses are asymptomatic, on occasion the virus can give rise to extensive outbreaks of mild illness characterized by fever, anorexia, serous nasal discharge, hind limb edema, stiff gait, scrotal edema, submandibular lymphadenopathy and urticarial skin rash. Affected horses may develop some or all of these clinical signs. Regardless of severity, the disease is non-fatal and complete clinical recovery occurs within 7 to 14 days. Symptomatic treatment is seldom indicated. Based on the outbreak recorded in India, there was no evidence that Getah virus is abortigenic in the pregnant mare or that infection can result in congenital abnormalities in foals.

The only other animal species in which Getah virus has been implicated in causing disease is swine. The virus has been isolated from newborn piglets that died of peracute disease and also from dead fetuses removed from a naturally infected sow.

Getah virus is primarily a mosquito-borne infection that is transmitted by different species of Culex and Aedes mosquitoes depending on the geographic region of the world in which it occurs. Swine are thought to play a role in amplification of the virus in endemic areas. The potential for transmission through direct horse-to-horse contact cannot be discounted considering some acutely infected horses shed significant quantities of infectious virus into the respiratory tract.

Diagnosis of Getah virus infection can be readily accomplished by virus detection in nasal swabs, unclotted blood (buffy coat) samples, and saliva either by PCR assay or virus isolation. It can also be confirmed by serological testing of acute and convalescent serum samples. Because of the close clinical similarity between Getah virus infection and equine viral arteritis and African horse sickness, it is important to differentiate it diagnostically from either of these two diseases.

Prevention and control of Getah virus infection is based on measures to reduce mosquito contact with horses and, optimally, vaccination of at-risk equine populations in countries in which the virus is endemic.

While Getah virus is not considered an important equine pathogen, it can be significantly disruptive when extensive outbreaks occur.

This article was written by Dr. Peter Timoney of the Gluck Equine Research Center. 

It was first published in the Equine Disease Quarterly, published by the University of Kentucky College of Agriculture, Food and Environment Department of Veterinary Science and sponsored by Lloyd’s of London and its Kentucky agents. You may subscribe to this publication for free.

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Dr. Peter Timoney