Department of Virology, National Veterinary Research Institute, Al. Partyzantow 57, 24-100, Pulawy, Poland.
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
Virol J. 2018 Jul 11;15(1):106. doi: 10.1186/s12985-018-1018-3.
Equid herpesviruses (EHVs) are widespread in equine populations worldwide. While the infection with equine α-herpesviruses (EHV-1 and EHV-4) has been linked to several clinical outcomes, the pathogenic potential for equine γ-herpesviruses (EHV-2 and EHV-5) is still unclear. The objective of the current study was to determine the prevalence of infection with EHVs among Polish horses, to investigate factors associated with EHV infections among horses sampled, and to determine genetic variability within Polish EHV-2 isolates.
Virus-specific real-time PCR assays were used for detection of EHV-1, EHV-2, EHV-4 and EHV-5 in nasal swabs collected from 540 horses from 13 national horse studs located throughout Poland. A proportion of EHV-2/5 positive samples were subjected to virus isolation followed by amplification and analysis of partial glycoprotein B sequence.
Overall, 448/540 (83.0%) horses sampled were positive for at least one virus. The most prevalent was infection with EHV-2 (77.2%), followed by EHV-5 (47.0%), and EHV-4 (0.4%). None of the horses was positive for EHV-1. Approximately half of the virus-infected horses were positive for both EHV-2 and EHV-5. The proportion of EHV-2/5 positive horses varied by age, breed, and season. Only 8.0% of horses sampled, mostly Arabians, showed clinical signs of respiratory disease at the time of sampling. The viral load of both EHV-2 and EHV-5 DNA was highest in swabs from young horses, which was particularly evident for EHV-2 infected foals. Mean viral loads in nasal swabs collected from diseased horses were higher than in swabs from healthy horses. That was also true for EHV-2 when only diseased Arabian foals were considered, but the levels of EHV-5 DNA were lower in swabs from diseased than from healthy foals. In agreement with other studies, there was a considerable variability between Polish EHV-2 sequences, with no clustering of sequences from horses with different health status. The level of EHV-2 variability seemed to differ between different studs/breeds.
The presence of foals and yearlings on a property is likely to increase the risk of active EHV-2/5 infection among in-contact horses. The existence of breed-specific differences in susceptibility to EHV-2/5 infections should be further investigated, as it may provide one variable that needs to be considered in attempts to associate EHV-2/5 infections with disease. Overall, the data presented add to the existing knowledge of the epidemiology and biology of equine γ-herpesviruses, with the long-term goal of better understanding of the pathogenesis and the impact of infections with these viruses on the well-being of the horse.
马疱疹病毒（EHVs）在全球马群中广泛存在。虽然马α疱疹病毒（EHV-1 和 EHV-4）的感染与多种临床结果有关，但马γ疱疹病毒（EHV-2 和 EHV-5）的致病潜力仍不清楚。本研究的目的是确定波兰马中 EHV 感染的流行情况，调查与所采样马 EHV 感染相关的因素，并确定波兰 EHV-2 分离株的遗传变异。
使用针对 EHV-1、EHV-2、EHV-4 和 EHV-5 的病毒特异性实时 PCR 检测法，从来自波兰 13 个国家马种研究站的 540 匹马的鼻拭子中进行检测。对部分 EHV-2/5 阳性样本进行病毒分离，随后进行糖蛋白 B 部分序列的扩增和分析。
总体而言，540 匹采样马中，448/540（83.0%）至少感染了一种病毒。最常见的是 EHV-2 感染（77.2%），其次是 EHV-5（47.0%）和 EHV-4（0.4%）。没有马匹呈 EHV-1 阳性。约一半的病毒感染马同时呈 EHV-2 和 EHV-5 阳性。EHV-2/5 阳性马的比例随年龄、品种和季节而变化。采样时，只有 8.0%的马（主要是阿拉伯马）表现出呼吸道疾病的临床症状。EHV-2 和 EHV-5 DNA 的病毒载量在幼马的拭子中最高，这在 EHV-2 感染的幼驹中尤为明显。患病马的鼻拭子中的病毒载量高于健康马的病毒载量。对于只考虑患病阿拉伯幼驹的情况也是如此，但患病幼驹的 EHV-5 DNA 水平低于健康幼驹。与其他研究一致，波兰 EHV-2 序列之间存在相当大的差异，不同健康状况的马的序列没有聚类。EHV-2 变异的程度似乎在不同的马种/品种之间有所不同。
在马场内存在幼驹和幼龄马，可能会增加接触马群中 EHV-2/5 活跃感染的风险。需要进一步研究马对 EHV-2/5 感染的易感性是否存在品种特异性差异，因为这可能是将 EHV-2/5 感染与疾病相关联时需要考虑的一个变量。总的来说，所提供的数据增加了对马γ疱疹病毒的流行病学和生物学的现有认识，长期目标是更好地了解这些病毒的发病机制及其对马健康的影响。
