Abstract:
Clinical, virological and serological responses were investigated in five pregnant donkey mares after
experimental exposure to the South African asinine-94 strain of equine arteritis virus (EAV), and the
duration of maternal immunity to EAV was studied in their foals.
In four intranasally inoculated mares, fever with maximum rectal temperatures of 39,1-40,7°C was
recorded 2-11 d after challenge. All the inoculated mares developed mild depression, and a serous
ocular and nasal discharge; in three mares mild conjunctivitis was observed. The virus was recovered
from the nasopharynx and from buffy-coat samples of all the mares 3-10 d, and 2-16 d post
inoculation (p.i.), respectively. Seroconversion to EAV was detected on days 8- 10 p.i. Peak serum-virus-
neutralizing antibody titres of log₁₀1,8-2,4, and lgG ELISA OD values of 0,85-2,15 were recorded
2-3 weeks p.i. The in-contact (p.c.) control mare developed fever on days 15-19 post exposure,
and showed mild clinical signs of equine viral arteritis similar to those observed in the inoculated
mares. Seroconversion to EAV was detected in the p.c. mare on day 20 post exposure, and virus
was isolated from nasal swabs and blood samples collected at the time of the febrile response and
1-3 d afterwards. None of the mares aborted. After they had given normal birth 45-128 d p.i. or after
p.c. exposure, no virus could be isolated from their placentas. The concentration of EAV-neutralizing
antibody in colostrum was two to eight times higher than in serum samples collected at the time
of parturition.
All the foals born to infected mares were clinically normal at the time of birth and throughout the
subsequent 1-2 months of observation. No EAV was recovered from the bully-coat fraction of
blood samples collected at birth nor from those collected on days 1, 2 and 7 after birth. Also, no virus-serum-
neutralizing or lgG ELISA antibody to EAV was detected in sera collected immediately after
birth before the foals started nursing. The colostrum-derived maternal antibodies against EAV gradually
declined and could not be detected by either the VN test or ELISA for 2-3 months after birth.
This study demonstrates that the asinine-94 strain of EAV does not cause abortion in pregnant
donkey mares. Furthermore, no carrier state could be demonstrated in foals born to mares infected
at the time of pregnancy.
