Response of pregnant mares to equine herpesvirus 1 (EHV1).

The research article focuses on studying the impact of the equine herpesvirus 1 (EHV1) on pregnant horses, with the findings showing that while most of them get infected, only a small fraction abort virus-infected fetuses.

Experimental Procedure and Findings

• Researchers exposed twenty-one pregnant mares to the EHV1 virus to evaluate the health impacts. The results showed that 19 out of 21 mares became infected as indicated by visible clinical signs and/or the presence of the virus in the blood.
• However, surprisingly, only one of the infected mares aborted a virus-infected fetus, suggesting that the virus does not directly lead to a high abortion rate amongst the infected mares.

Specific Characteristics of EHV1 Infection in Mares

• The infection was found to be leukocyte-associated, meaning it remained associated with the white blood cells in the horses’ bodies. This appeared to lead to non-productive, latent infections of these cells.
• The researchers found that the infectivity of the virus, which was detectable by a laboratory technique called cocultivation, remained persistently in the circulating leukocytes (white blood cells) for as much as nine days. However, it did not result in an abortion in these cases.

Challenges in Vaccine Efficacy Evaluation

• The results raise challenges for assessing the efficacy of vaccines intended to prevent EHV1-induced abortion, as it is hard to find non-exposed mares for a comparison group.
• The study also emphasized the lack of tests that measure the residual protection of a vaccine, making it more difficult to evaluate vaccine effectiveness against this virus.
• Moreover, the researchers pointed out the incomplete understanding of the pathogenic mechanisms involved in causing abortion due to this virus, which further complicates the issue of vaccine efficacy evaluation.