Origin of the hemagglutinin on A/Equine/Johannesburg/86 (H3N8): the first known equine influenza outbreak in South Africa

Abstract

A severe influenza outbreak occurred in horses in South Africa in 1986. The causative agent was identified as an influenza virus [A/Equine/Johannesburg/86 (H3N8)]. Antigenic analyses of the hemagglutinin (HA) with ferret antisera and monoclonal antibodies showed that the Eq/Johannesburg/86 virus is similar to recent equine H3 viruses. The nucleotide sequence analysis on the HA genes of Eq/Johannesburg/86 and other equine H3 influenza viruses, together with the epidemiological data, clearly demonstrated that the Eq/Johannesburg/86 virus was derived from a virus that had been circulating in horses in the United States in 1986–87. The epidemiological information suggests that the unusually severe influenza outbreak in South Africa may be due to the lack of immunity to these viruses in the horse population.