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African Horse Sickness

AHS was first described by Theiler in 1921, when he related seven major epizootics of AHS in South Africa between 1780-1918. Currently the disease is endemic in sub-Saharan Africa occurring annually or seasonally wherever susceptible Equidae are present. About every 20 years, major outbreaks occur in southern Africa and occasionally northern Africa. In 1959-61, the first documented outbreak of AHS out of its traditional enzootic region of Africa occurred in the Middle East (Israel, Iran, Pakistan, Afghanistan, India, Turkey, Iraq, Syria, Lebanon, Jordan, and Cyprus). During this outbreak, as many as 300,000 animals died or were destroyed. India reported a 90% mortality in Equidae involved. Another outbreak of AHS occurred in 1965-66 in the North African countries of Morocco and Algeria and also in Spain. Spain had another outbreak of AHS in 1987 (which later spread to Portugal). It is suspected that the disease reached the country via zebras imported from Namibia, Africa, which were subclinically infected with the virus. [Zebras show no clinical signs when infected with the virus but can have viremia (and therefore be infectious for the vector) for as long as 6 weeks!]. During this outbreak, the disease was also effectively spread by a non-traditional Culicoides species. This led to an increase in the list of potential vectors capable of transmitting the disease. Recent outbreaks of AHS have occurred in Algeria (1989) and Morocco (1989-91). However the disease has not occurred in these countries since 1991.

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