engleski

An equine herpesvirus type 1 (EHV-1) abortion outbreak caused by a neuropathogenic strain in vaccinated mares

From February to July 2014 neuropathogenic strain of EHV-1 was confirmed as a cause of abortion on the same breeding farm were in 2009 EHV-1 abortion storme was described. All aborted mares with confirmed EHV-1 abortion 2014 were aged between 13 and 16 years and were resident on breeding farm during outbreak 2009. Since no entry of new animals and no transport of resident horses abortion outbreak is probably caused by viral reactivation of the same virus that is present on the breeding farm since 2009. This thesis is supported by 100% identically nucleotide sequences of neuropathogenic EHV-1 isolated from aborted foetus with isolates from outbreak 2009 on the same breeding farm. Absence of clinical signs other than abortion is in accordance with significant influence of breed on clinical manifestation of neuropathogenic EHV-1 infection described during outbreak 2009. Since outbreak in 2009 all horses on breeding farm were annually vaccinated and pregnant mares, including six that have aborted during 2014 outbreak, were vaccinated in months 5, 7 and 9 of gestation. Cases of abortion outbreaks as a consequence of EHV-1 infection in regularly vaccinated mares are described as well as abortion in single animals as a consequence of local reactivation of infection. In this outbreak, abortions were consequence of local reactivation of virus in six animals five years after primal infection despite regularly vaccination during this period. Reactivation of latent EHV-1 in six animals in the same season must include some other risk factors in pathogenesis of EHV-1 infection. Even though risk factors for reactivation of the EHV-1 infection are still not clarified little is known about the potential adverse effects of administering a potent vaccine too frequently, which may attenuate the immune response. Further studies must be done to validate existing vaccination recommendations and influence of frequent vaccination to reactivation of latent EHV-1 infection.

EHV-1; mares; abortion; reactivation; vaccinal failure

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