Gammaherpesvirus infections in equids: a review

Abstract

Although the first equine gammaherpesvirus was identified over 50 years ago, the isolation and characterization of other members of this virus group has been relatively recent. Even so, numerous clinical syndromes have been identified in equid species in association with these viruses. Equid gammaherpesviruses are a genetically heterogeneous viral subfamily, the function of which in host immune modulation and disease pathogenesis has not yet been elucidated. While they share similarities with gammaherpesviruses in humans, the role they play in their relationship with the host is the subject of continued interest and research. Their widespread presence in horses and other equid species provides a considerable challenge in linking them with particular clinical and pathological conditions and in defining their significance from a diagnostic and therapeutic viewpoint. The present review provides an update on the taxonomy, epidemiology, and clinical syndromes, especially respiratory, reported in association with gammaherpesvirus infection in horses, donkeys, and other equid species.

Noninvasive Detection of Equid Herpesviruses in Fecal Samples

“…Alphaherpesvirinae subfamily are typically associated with more-severe outcomes (5,7,8). Acute EHV infection can cause clinical signs including pharyngitis, pneumonia, pyrexia, lymphadenopathy, abortion, and neuropathies due to acute myeloencephalopathy (3,5,9,10). Furthermore, it has been shown that EHVs can occasionally infect a range of nonequid species in captivity, with potentially fatal outcomes (11)(12)(13)(14)(15)(16).…”

“…However, herpesviruses can be reactivated (17), leading to shedding of infectious virus into the environment. In equids, nasal shedding is predominant and can be accompanied by viremia; thus, testing nasal swabs and invasive samples such as blood is considered the most reliable method for monitoring EHV shedding in horses (3,10). Sampling wild equids generally requires invasive procedures due to the necessity of physical restraint, which can cause severe stress or risk to animal health for large mammals (19,20).…”

First description of a herpesvirus infection in genus Lepus

“…On the other hand, animal experimentation is complicated by the absence of available specific pathogen free (SPF) specimens, and by the difficulties in keeping hares in captivity, limiting cause-effect experiments. Moreover, during latency, herpesviruses may not be detected by current methods as it is the case of gammaherpesvirus in horses, resulting in an underestimated prevalence in the populations [27] , [28]. Reports indicate that equine herpesvirus 2 (EHV-2) can be detected According to our study, based on viral DNA amplification, around half of animals tested (63% symptomatic and 37% asymptomatic) were positive for LeHV-5.…”

“…In addition, herpesviruses are frequently found either in the absence of clinical signs or in association with very diverse clinical signs [27].This fact muddles the understanding of the true role and relative contribution of many herpesviruses in the courses of certain diseases, especially with regards to wild species that are often exposed to, and infected by, many pathogens. On the other hand, animal experimentation is complicated by the absence of available specific pathogen free (SPF) specimens, and by the difficulties in keeping hares in captivity, limiting cause-effect experiments.…”

Potential Outbreak in Brazil by Equine Herpesvirus Type 2 (EHV-2): Detection, Clinical and Genetic Analysis of Equine Gammaherpesvirus 2

“…However, Marenzoni et al(19) detected EHV-1 and EHV-5 in 14% (9 animals) with different reproductive problems, including one co-infection with EHV-1 and EHV-2. The same authors detected the presence of EHV-5 in non-pregnant uterus, implying that it may have a role in reproductive dysfunction and have a negative consequence on the pregnant uterus.…”