In the Kruger National Park 75% of zebra foals are born in October-March and they lose their passive immunity against African horsesickness virus (AHSV) when they are 5-6 months old. One month later
infection with different serotypes of AHSV amounts to 31% and thereafter infections increase rapidly to
almost 100% before the foals are 12 months old. The capability of zebra to maintain AHSV is clearly
illustrated by the continuing infections during every month of the year with a peak period in winter. This
peak is ascribed to the presence of large numbers of susceptible foals in the presence of active Culicoides
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