Abstract
African horse sickness (AHS) is a vector‐borne disease transmitted by Culicoides spp., endemic to sub‐Saharan Africa. There have been many examples of historic and recent outbreaks in the Middle East, Asia and Europe. However, not much is known about infection dynamics and outbreak potential in these naive populations. In order to better inform a previously published ordinary differential equation model, we performed a systematic literature search to identify studies documenting experimental infection of naive (control) equids in vaccination trials. Data on the time until the onset of viraemia, clinical signs and death after experimental infection of a naive equid and duration of viraemia were extracted. The time to viraemia was 4.6 days and the time to clinical signs was 4.9 days, longer than the previously estimated latent period of 3.7 days. The infectious periods of animals that died/were euthanized or survived were found to be 3.9 and 8.7 days, whereas previous estimations were 4.4 and 6 days, respectively. The case fatality was also found to be higher than previous estimations. The updated parameter values (along with other more recently published estimates from literature) resulted in an increase in the number of host deaths, decrease in the duration of the outbreak and greater prevalence in vectors.
Highlights
African horse sickness (AHS) is caused by African horse sickness virus (AHSV) of the genus Orbivirus in the family Reoviridae
None of these tests gave a significant result (p < .05); we conclude that there is no evidence that the time until viraemia, the onset of clinical signs or death varies between serotypes or inoculation method
A paired t-test showed that there was no significant difference between the start of viraemia between polymerase chain reaction (PCR) and virus isolation methods in the six equids for which both were compared (t = −1.55, df = 6, p = .17)
Summary
African horse sickness (AHS) is caused by African horse sickness virus (AHSV) of the genus Orbivirus in the family Reoviridae. Endemic to subSaharan Africa, it often emerges when periods of heavy rain follow hot and dry conditions. This favours its principle vector, Culicoides spp., with Culicoides imicola usually considered to be the most important vector species in Africa (Mellor & Hamblin, 2004). Outbreaks in central and East Africa have occasionally spread to Egypt, the Middle East and southern Arabia (Mirchamsy & Hazrati, 1973). A further epidemic of AHSV in northwest Africa (Morocco, Algeria and Tunisia) in 1965−1966 spread briefly to southern Spain but was eliminated by vaccination and by killing infected equids (Hazrati, 1967). The first occurrence of an outbreak outside Africa not caused by serotype 9 was Transbound Emerg Dis. 2021;1–11
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