REASONS FOR PERFORMING STUDY : EHV-1 is one of the most common causes of
infectious abortion in mares. Analyzing the demography of outbreaks and detailing
subsequent reproductive performance of affected mares will assist in the
management of future (threatened) epizootics.
OBJECTIVES : To examine the epidemiology and reproductive outcomes of two EHV-1
abortion epizootics with very different patterns of morbidity. Study design: Epidemiological and reproductive data were analyzed retrospectively
following abortion epizootics associated with EHV-1, but initiated via different routes,
among unvaccinated mares on two Thoroughbred farms in South Africa.
METHODS : Aborting mares were assigned to either the EHV-1 abortion cohort via
positive immunostaining (farm 1 and 2) or qPCR (farm 2) on tissue samples, or to
the non-EHV abortion cohort.
RESULTS : During their respective epizootics, EHV-1 abortions affected 9/30 (30.0%)
and 18/316 (5.7%) of the pregnant mares on farms 1 and 2 respectively; there were
also 25 (7.9%) non-EHV abortions on farm 2. Epizootic differences included:
durations (farm 1 = 135 d; farm 2 = 34 d), intervals between first and subsequent
abortions (farm 1 = 39 d; farm 2 = 2 d), and intervals to confirmation of EHV-1 (farm
1 = 40 d; farm 2 = 2 d). The median age of EHV-1 abortion mares (8.0; 5-18 years)
in both epizootics was similar, but significantly younger (P= 0.004) than the 25 non-
EHV-1 abortion mares (11.0; 4-24 years) on farm 2. Gestation stage (median; range)
of EHV-1 (291.5; 277-313) and non-EHV-1 (211.9; 61-339 d) abortions were
significantly different (P=0.001). The post-abortion complications and subsequent
reproductive outcomes had no significant association with EHV-1 abortion.
CONCLUSIONS : The marked difference in morbidity between the two epizootics may
be associated with routes of introduction or intervention strategy dictated by
availability of molecular diagnostic techniques. Unexpectedly, EHV-1 was not more
commonly associated with post-abortion complications.