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African Horse Sickness in Thailand

Christian Fernsby |
Thailand reported an outbreak of African Horse Sickness (AHS) on 27 March, in horses from multiple barns across the district of Pak Chong, in the north eastern region of the country.

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This is the first time that AHS has been confirmed in Thailand, a country which has OIE official free status for AHS and is on the approved list for exports of equines to the EU.

The Thai authorities reported that out of 341 horses, 62 were infected and 42 died. Unofficial sources report these to be race horses.

The source of virus is not currently known, although epidemiological investigation is ongoing and samples have been taken for serotyping.

There are at least nine different strains of AHS, with different geographical distribution, therefore strain identification may point to the region where virus originated. All movements of equids within 150km of the outbreak have been restricted and guidance on improving biosecurity, is being communicated (HorseTalk, 2020).

Nearby countries are also improving awareness amongst equine owners and making recommendations for increased biosecurity and vigilance (NST, 2020).

African Horse Sickness (AHS) is a vector-borne viral disease, affecting all species of equidae; it has never occurred in the UK and the UK has OIE official free status. AHS is transmitted by certain species of midges, most commonly Culicoides imicola (which is usually restricted to the southern parts of Europe, but otherwise found throughout Africa and Asia).

Other possible vectors include C.brevitaris, C.sonorensis and C.obsoletus (present in the UK) (Mellor and Hamblin, 2004).

AHS is endemic in sub-Saharan Africa, but historically outbreaks of AHS have been reported outside this region, in the Iberian Peninsula, North Africa, the Middle East, Cyprus, Turkey, Pakistan, Afghanistan and India.

The disease, however, has not persisted in these areas.

The severity of clinical signs depends upon the virus strain and host species.

The fatality rate in horses can reach 90% in epidemics, but is less in mules and donkeys. Zebra usually do not show clinical signs, but act as reservoirs of infection.

Virus circulation is usually seasonal and associated with hot and humid weather and abundance of the arthropod vectors.

Commercial vaccines against AHS are available, but are not approved for use in the EU.

This is Thailand’s first reported case of AHS. Thailand has OIE official free status, and is approved to export registered and breeding horses to Europe as a Group C country and re-entry following temporary admission for competitions.

The export certificate requires that entry is only allowed from areas that are free of AHS. â– 

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