Recent advancements in our understanding of equid gammaherpesvirus infections

Abstract

The reported prevalence is usually higher for EHV-2 infections than EHV-5. Despite being widespread there is still little known about the role of the equine gammaherpesviruses in disease pathogenesis and modulation of the host's immune system. Interpreting the significance of EHV-2 and EHV-5 detection is further complicated by their discovery in immunocompetent horses that do not display associated clinical signs. [1][2][3][4][8][9][10][11][12] Equine gammaherpesviruses are associated with several disease processes but it is currently unclear whether they are the inciting cause of the disease, co-factors or innocent bystanders. Defining their pathogenesis and mechanisms of immune system evasion is central to determining their importance and in formulating suitable therapeutics. This review examines the key challenges currently facing equine gammaherpesvirus research, the recent advancements that have been made in our understanding of the significance and pathogenesis of these viruses and future research directions. | Virus and genome structureThe family Herpesviridae is subdivided into three subfamilies:Alphaherpesvirinae, Betaherpesvirinae and Gammaherpesvirinae.EHV-2 and EHV-5 are classified in the genus Percavirus within the Gammaherpesvirinae subfamily. 13 Herpesviruses usually have a narrow host range and are restricted to the order or family to which the natural host belongs. Currently, there are 12 herpesviruses that have the potential to infect equids (Figure 1). The horse is the natural host for five of these viruses (EHV-1, EHV-2, EHV-3, EHV-4 and EHV-5).

Detection of Equine Papillomaviruses and Gamma-Herpesviruses in Equine Squamous Cell Carcinoma

“…Similarly, AsHV5 has been found in symptomatic and asymptomatic equids [ 32 ]. Detection of EHV2, EHV5, and AsHV5 in clinically normal equids and individuals with various disease symptoms has seriously hampered the establishment of virus type-specific etiopathological associations for a long time [ 28 ]. Studies on a possible role of these or other herpesvirus types in SCC development and progression have not been conducted so far.…”

“…The rationale underlying the choice of control material was that EcPV2 can be detected in this material in horses bearing EcPV2-positive SCCs, related precursor lesions, and occasionally tumor-free individuals [ 20 , 24 , 25 , 26 ], and that herpesvirus DNA is commonly found in epithelial swabs and body fluids from healthy horses [ 5 , 27 , 28 , 29 , 30 , 31 , 32 ].…”

Macrodendritic ulcerative keratitis and conjunctival lymphoid hyperplasia in horses with equine herpesvirus‐2 and equine herpesvirus‐5 infections

“…1 Both viruses are frequently detected in healthy and diseased horses and, with the exception of the strong link between EHV-5 and the development of the severe condition equine multinodular pulmonary fibrosis in adult horses, their etiological role in most other clinical diseases is currently unclear. 2,3 Both EHV-2 and EHV-5 have been suggested as the cause of many clinical syndromes, including upper respiratory tract disease, poor performance, and ocular surface disease in foals and adult horses. [4][5][6][7][8] Clinical investigations describe the detection of EHV-2 and EHV-5 in horses with naturally acquired conjunctivitis and horses experimentally infected with EHV-2 are described to develop acute conjunctivitis.…”

“…Equine herpesvirus‐2 (EHV‐2) and equine herpesvirus‐5 (EHV‐5) are gammaherpesviruses that are ubiquitous in horse populations worldwide 1 . Both viruses are frequently detected in healthy and diseased horses and, with the exception of the strong link between EHV‐5 and the development of the severe condition equine multinodular pulmonary fibrosis in adult horses, their etiological role in most other clinical diseases is currently unclear 2,3 . Both EHV‐2 and EHV‐5 have been suggested as the cause of many clinical syndromes, including upper respiratory tract disease, poor performance, and ocular surface disease in foals and adult horses 4–8 …”

Colonic T-cell–rich, large B-cell lymphoma associated with equid herpesvirus 5 infection and secondary trans-colonic fistula in a horse

“…20 Pulmonary fibrosis has been reproduced by experimental infection of horses with EHV5, and it has been proposed that fibrosis is a consequence of EHV5 viral latency within the lungs. 6,23…”