African horse sickness at a glance
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African horse sickness (AHS) is an infectious but non-contagious viral disease, transmitted by Culicoides, affecting all species of equidae. Rates of fatality in naive horse populations can reach 80-90%,which ranks AHS as among the most lethal of viral infections known in horses.
The disease is caused by an Orbivirus of family Reoviridae. Nine virus serotypes of AHSV are known. The clinical disease caused by AHSV is usually classified into four forms according to characteristic pathology and varies according to host species as well as prior exposure to the specific serotype of AHSV.
The horse is the soliped most susceptible to the disease and species of zebra and the African donkey are primary maintenance reservoirs of AHSV. It is not known to affect humans.
AHS is endemic in Sub-Saharan African countries, specially in southern countries where all nine serotypes occurs. Serotypes 9, 4 and 2 have been found in North and West Africa from where they occasionally spread into countries surrounding the Mediterranean. Examples of outbreaks that have occurred outside Africa are: in the Middle East (1959–1963), in Spain (serotype 9, 1966, serotype 4, 1987–1990) and in Portugal (serotype 4, 1989). Recently, in the early months of 2020, an unexpected outbreak of AHS appeared in Thailand, affecting to Malaysia too, and threatens the equine industry worldwide.
Vaccination with live attenuated strains of AHSV is the primary means of controlling AHS in both endemic and epidemic scenarios. Due to the disadvantages of live attenuated vaccines, a wide range of other vaccine candidates have been trialed, but none have been used in the field to date, primarily owing to a lack of commercial viability.
