Abortions
Bacterial-related abortions
a) Nocardia spp.
A study performed by Erol et al. (2012) at the University of Kentucky Veterinary
Diagnostic Laboratory in the United States revealed a record number of abortions in
mares due to nocardioform placentitis in 2011 and provided direct evidence of the
significance of these organisms in equine abortions.
A total of 79 cases tested positive for nocardioform placentitis, of which most of the
nocardioforms were unknown species.
Amycolatopsis spp. were responsible for the highest number of abortions, while
Crossiella equi was abundant, and a small percentage of cases were associated with
both these microorganisms (nocardioforms).
Virus-related abortions
a) Equine Encephalosis Virus (EEV)
Equine Encephalosis Virus has also been associated with equine foetus abortions
within five to six months of the gestation period (Viljoen and Huismans, 1989).
Equine encephalosis virus may also be involved in early and/or undetected abortion
in mares, which may be misdiagnosed as infertility, for instance. However, there has
been no direct evidence of this until the year 2013.
The WDL and the Equine Research Centre described three cases in the Western
Cape (South Africa) where EEV was considered to be the primary cause of abortion
in thoroughbred mares that were mid-term in gestation. The presence of EEV was
detected by an EEV specific RT PCR technique that displayed the presence of EEV
in placental tissue as well as in organ necropsy samples of the aborted foetuses.
This is the first reported evidence of EEV-related abortions in horses and provides
insight in the mode of transmission of the virus from the mare to the unborn foetus.
Contrary to scientific publications describing EEV as a ‘mild’ disease in adult horses
for more than a century now, our r esearch demonstrated that EEV disease outbreaks
lead, directly and indirectly, to abortions in thoroughbred horses with a prevalence of
66.7% EEV positives by PCR testing in fifteen mares that aborted after displaying
symptoms of viraemia. None of the case study animals tested positive for African
Horse Sickness Virus, Equine Herpes Virus 1&4 or West Nile Virus (Table 3).
The case study mares sampled in this study displayed the symptoms of listlessness
and fever as previously described by Erasmus et al., 1970. Post mortem necropsy
samples of liver and kidney tissue of the aborted foetuses that were infected with
EEV, Foal B and Foal C (Table 2), also displayed autolysis and haemorrhage (Table
5), which is in accordance to the symptoms of venus congestion of liver and kidney
tissue described previously (Erasmus et al., 1970; and Viljoen and Huismans, 1989).
EEV serotype-specific or multiserotype vaccines effective against EEV strains
previously identified (Aharonson-Raz et al., 2011; Howell et al., 2008; Van Niekerk et
al., 2003) may prevent indirect and direct EEV-associated foetal death. Such a
multiple serotype vaccine-induced protective immunity may for instance ‘relieve’ the
EEV immune response or symptoms, such as fever and haemorrhage, in pregnant
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
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