Malignant Catarrhal Fever (MCF) is an often fatal lymphoproliferative disease that primarily affects cattle and other ruminants. The causative agent of MCF is Ovine Herpesvirus-2 (OvHV-2), which is carried asymptomatically by most sheep(Smith et al., 2015; Baxter et al., 1993). Despite the lack of clinical symptoms in these reservoir hosts, OvHV-2 poses significant health risks to susceptible species, primarily cattle, wherein it can lead to the severe and often fatal condition known as Sheep Associated Malignant Catarrhal Fever (SA-MCF) (Powers et al., 2005; Reid et al., 2004). Transmission of OvHV-2 from sheep to susceptible species like cattle results in clinical MCF characterized by fever, oral ulcerations, ocular and nasal mucopurulent discharge, and lymphoid neoplasia (Taus et al., 2015).
OvHV-2 is a gamma-herpesvirus carried lifelong by sheep after initial infection. While sheep remain asymptomatic carriers, the virus can cross species barriers to cause MCF in cattle, bison, deer, and other ruminant species (Davison et al., 2009; Reid et al., 1989). The global distribution and economic impact of MCF in cattle operations makes understanding the molecular epidemiology and genetic diversity of circulating OvHV-2 strains crucial.
The glycoprotein B (gB) is a highly conserved envelope protein involved in virus entry and cell fusion, making it an important target for molecular characterization (Huang et al., 2017). Previous studies have reported genetic variations in the gB gene among OvHV-2 isolates from different geographic regions (Taus et al., 2015). However, limited information is available on the molecular characteristics of OvHV-2 strains circulating in sheep and cattle populations in the Jammu and Kashmir region of India.
Molecular detection techniques, such as Polymerase Chain Reaction (PCR), have proven invaluable in identifying and characterizing viral pathogens at the genetic level (Baxter et al., 1993; Crawford et al., 1999). These methods offer sensitivity and specificity, allowing for the detection of OvHV-2 in asymptomatic carriers, thus highlighting the virus's distribution and prevalence across different populations (Wiyono et al., 1994).
Furthermore, phylogenetic analysis plays a crucial role in understanding the evolutionary dynamics of OvHV-2, offering insights into the genetic diversity and potential transmission pathways of the virus (McGeoch et al., 1995; Kumar et al., 2016). By analyzing the sequences of the glycoprotein B (gB) gene, researchers can uncover the genetic relationships between OvHV-2 strains from various geographical locations and host species, shedding light on the virus's evolutionary history and mechanisms of host adaptation ( Doe et al., 2018).
Given the economic and health implications of OvHV-2 infections in livestock, particularly in regions where mixed farming practices are common, such as in the Kashmir valley, it is imperative to undertake comprehensive studies aimed at the molecular detection and phylogenetic characterization of OvHV-2 (Jones et al., 2017). This research not only contributes to the body of knowledge surrounding OvHV-2 but also aids in the development of targeted surveillance and control measures to mitigate the impact of SA-MCF on affected livestock populations.
The literature surrounding Ovine Herpesvirus-2 (OvHV-2) and Malignant Catarrhal Fever (MCF) is extensive, with studies spanning several decades (Cleaveland et al., 2001; Sood et al., 2017). These studies have provided a foundation for understanding the disease's epidemiology, pathogenesis, and molecular characteristics. However, the focus on sub-clinical infections in cattle and sheep, particularly in mixed farming systems, remains less explored (Reid et al., 2004; Smith et al., 2015).
In this study, we investigated the presence of OvHV-2 in sheep and cattle populations in Jammu and Kashmir by screening for the viral polymerase gene. We subsequently amplified, cloned, and sequenced the full-length gB gene and an inner fragment from positive samples. Comparative sequence and phylogenetic analyses were performed to characterize the genetic diversity of the circulating OvHV-2 strains in relation to previously reported strains from India and other countries.