EXPERIMENTAL EXPOSURE OF PREGNANT MARES TO THE ASININE-94 STRAIN OF EQUINE ARTERITIS VIRUS

Clinical, virological and serological responses were evaluated in 10 p regnant mares after different challenge exposures to the asinine-94 st rain of equine arteritis virus (EAV). The outcome of maternal infectio n on the progeny was also investigated. Mares were inoculated intranas ally (n = 4), intramuscularly (n = 2), intravenously (n = 1), or conta ct-exposed (n = 3). All inoculated mares developed pyrexia, 5 showed m ild clinical signs related to EAV infection and 2 remained asymptomati c. Viraemia was detected in all the inoculated animals and shedding of virus from the respiratory tract occurred in 6. Five mares were re-ch allenged intranasally 7 and 15 weeks after inoculation. Clinical signs of the disease in these mares were limited to mild conjunctivitis. Af ter re-challenge, virus was recovered from buffy coat cultures of 2 ma res 2-6 days after re-infection. EAV was not recovered from colostrum and milk samples during the Ist week post partum. All inoculated mares seroconverted to EAV 8-12 days post inoculation and also seroconverte d after re-challenge. No clinical signs of EAV infection were observed in the 3 mares kept in close contact during the post-inoculation and re-challenge periods. Serum neutralising antibody to the virus was det ected in 1 in-contact mare only, while a detectable concentration of s pecific IgG was found by ELISA in the colostrum of 1 of the other in-c ontact mares. Eight of the mares gave birth to clinically normal foals , although 1 was born prematurely. Shortly after birth, 7 foals develo ped fever and variable clinical signs; 5 foals became septicaemic and 3 of them died 2-5 days after birth, while the remaining 2 were euthan ased at 1 month of age. EAV was not recovered from the placenta, from buffy coat fractions of blood collected from foals immediately after b irth and 1-3 days later, or from a range of tissues taken from the 3 f oals that died and 2 that were euthanased. Virus was not isolated from tissues collected from 1 mate and her foetus 3 weeks after this mare was re-challenged.