Effect of the South African asinine-94 strain of equine arteritis virus (EAV) in pregnant donkey mares and duration of maternal immunity in foals

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 degrees 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 conjuctivitis was observed. The virus was recovered from the nasopharynx and from buffy-coat samples of all the mares 3-10 d, and 2-18 d post inoculation (p.i.), respectively. Seroconversion to EAV was detected on days 8-10 p.i. Peak serum-virus-neutralizing antibody titres of log10 1.8-2.4, and IgG 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 buffy-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 IgG 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.