Objective data plead to suspend import-bans for seroreactors against equine arteritis virus except for breeder stallions

A seroepidemiological test survey by micro-serumneutralization test for equine arteritis virus (EAV) was conducted in 4 breeds of horses. The incentive for the present investigation was successful isolation of EAV virus from 3 aborted fetuses, one each from three different breeds during 1989–90 in Austria. Randomly sampled sera of 130 riding horses revealed 12.1% cases positive to EAV. Contrarily, 78.1% of Austrian- borne Lipizzan mares from the stud, in which one of the virologically proved EAV-abortion had occurred, were seroreactors. Moreover, 51.6% of Lipizzan mares imported from 5 European countries, were also seropositive. Results also revealed high seroreactor rates in Austrian state- owned stallions, i.e. 55.6% of the Haflinger, 73.3% of the Noriker, 84.6% of the Warmblood and 93.3% of the Lipizzan stallions were seropositive to EAV. The data revealed that stallions did not acquire EAV infection from mares during their 4 months' covering stay on field stations. As no artificial insemination was practised, they could also not have contracted EAV from the artificial vagina. Furthermore, Lipizzan stallions are never used for breeding up to 18 years old, nevertheless they showed the highest reactor rates. Thus genital aquisition of EAV, on which literature has focussed these last years, does not account for the extremely high seroreactor rates determined. Instead, horizontal infection must have taken the central position in EAV epidemiology. Infection by EAV through aerosols from the respiratory tract has been known for close to 40 years. It is postulated that under the crowded stabling conditions prevalent for 70 Lipizzan stallions as well as for the 270 stallions kept at the Austrian National Stud, semen-shedders contaminated their bedding by masturbation, as is practised by idle stallions, which spread the EAV infection horizontally to neighbour stallions. The high reactor rates of Austrian Haflinger, Noriker and Warmblood stallions was of minimal or probably no impact on breeding success as well as on overall health of the Austrian horse population. Conception rates and birth rates recorded for 5 years for over 7000 mares served by state-owned stallions were normal. Similar observations on smaller number of horses, have very recently been reported from Australia, Norway and Sweden. Accordingly, hygienic measures were recommended by these countries including Austria. Present findings revealed that the import-bans as imposed by some countries for all EAV- seroreactors are scientifically untenable for mares and geldings which are never persistently infected.