African horse sickness (AHS), an OIE listed disease, has been reported in Thailand. It is a serious viral disease of horses and does not normally occur in countries other than sub-Saharan Africa. It has potential for serious and rapid spread and is important in the international trade of horses.

The virus is transmitted to horses by biting midges of the genus Culicoides. It is not spread by aerosol or direct contact between infected and noninfected animals and it does not infect humans. Wind can play an important role in dispersing infected insects and has been implicated in the international spread of previous AHS epidemics.

AHS commonly kills domestic horses and mules. Disease in donkeys is less severe. Zebras are recognised as the natural reservoir host.

The acute or ‘pulmonary’ form occurs in totally susceptible horses. It is characterised by high fever, excessive fluid in and around the lungs, difficult breathing and death of up to 95% of horses within 3–5 days.

Currently very few (if any) horses are moving internationally from anywhere. Grooms are unable to accompany and attend to the welfare of horses because of COVID-19 related travel bans on humans.

Control of AHS in Thailand may be challenging due to the climatic conditions and resource constraints given the concurrent existence of African swine fever and COVID-19 in the Asian region. Access to and advice from meteorological experts and entomologists would be useful to assess risks posed by windborne spread.

Thailand is receiving technical assistance from South African veterinary experts with experience in AHS control.

Dr Patricia Ellis
Consultant Technical Advisor
Asian Racing Federation

28 March 2020