Figure 1. A map of the zones within the African horse sickness (AHS)
Controlled Area of South Africa.
AHS is transmitted by small (1-3mm in size) biting midges (Culicoides spp.),
which are most active at dawn and dusk. In endemic areas the most
significant vectors are Culicoides imicola and C. bolitinos. The midges
become infected by taking blood meals from viraemic animals. The incubation
period in the midge (time between biting an infected horse and being able to
transmit to another horse) is around 8 to 10 days at around 25°C, after which
the virus localizes in the salivary glands of the midge and can then be
transmitted to another horse. The incubation period can be prolonged in lower
temperatur es. As the ambient temperature drops, the midge lifespan is
extended, but this drop in temperature also will decrease infection rate as well
as viral multiplication. At temperatures below 15°C AHSV does not replicate,
however, it can resume if temperatures rise again within the life span of the
midge. The exact time limit on this process is still unknown.
Wind-borne spread of infected midges may play a role in local spread of AHS.
Long-distance spread of AHS is usually the result of inadvertent movement of
Equidae infected with AHSV.
The incubation period in horses following natural infection with AHSV is
between 5 and 9 days. In susceptible horses mortality is 70 to 95% and the
prognosis is extremely poor. In mules the mortality is approximately 50% and
in European and Asian donkeys it is 5-10%. Mortality is very low in African
donkeys and zebra.
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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