Lateral and sexual transmission of EAV among horses and lateral transmission between donkeys and
horses were attempted by experimental infection with the South African asinine strain. Clinical, immunological
and virological responses were evaluated.
All intramuscularly inoculated horses developed very mild clinical signs, were viraemic, shed virus
from nasopharynx, and seroconverted. Lateral infection was demonstrated in one in-contact mare. Reinfection
of two stallions by intranasal instillation was shown by virus recovery from bully-coat cultures.
After nasal instillation of virus, one stallion which did not become infected by in-contact exposure,
showed slight serous nasal and ocular discharge, contained virus in a blood and nasopharynx
and seroconverted. Attempts to transmit the virus from seropositive stallions to seronegative mares
by breeding, were not successful; no virus was isolated from semen.
All inoculated donkeys and three in-contact horses showed clinical signs consistent with an EAV infection.
Although virus was isolated from donkey buffy-coat preparations and the nasopharynx, and
they seroconverted, no virus was isolated from the horses, and they failed to seroconvert; it was assumed
that their clinical signs were due to factors unrelated to EAV.
The South African strain of EAV appears to be poorly transmissible to horses, supporting the findings
of other field studies which indicate a widespread distribution and long-standing presence of the virus
among South African donkeys, but a very restricted prevalence of seropositive horses.