In the present study, Hemi-nested PCR was used to detect the OvHV-2 POL and ORF75 tegument protein genes in healthy sheep and goats. The prevalence of OvHV-2 positive samples was 16.7% and 13.5% in sheep and goats, respectively, with an overall prevalence of 15%.
There have been several published reports regarding the prevalence of OvHV-2 in Iran and neighboring countries. for the first time, Ramyar. H and Hesami. M reported MCF in the Cattel in 1973 by clinical signs and virus neutralization test in Iran [22]. According to the Momtaz et al. and Seyfi Abad Shapouri et al. researches, the prevalence of OvHV-2 in healthy sheep in central and western Iran was 100% and 82%, respectively, as determined using PCR [17, 23]. In a study on wild ruminants in Iran, Hemmatzadeh et al. reported that 31% of the samples were positive for OvHV-2 using PCR [16]. The prevalence of OvHV − 2 in Pakistan was 48% and 44% in sheep and goats, respectively, as determined by PCR [19]. Pekmez et al. reported a 34% prevalence of OvHV-2 in sheep using PCR on blood, organs, and aborted fetuses in Turkey [24]. Additionally, Khudhair et al. reported 100% and 86.6% prevalence of the virus in sheep and goats, respectively, from Al-Qadisiyah province in Iraq [14].
Goats are natural hosts of caprine herpesvirus 2 (CpHV-2) [2, 25]. However, as we detected OvHV-2 in this study, some evidence indicates that goats are reservoir hosts for OvHV-2 [17, 19, 26, 27], because mixed farming is common in this region, OvHV-2 may be transmitted between sheep and goats without any specific clinical signs. However, some studies have suggested that OvHV-2 can lead to subclinical infection in goats as well as exhibit clinical signs, such as fever and central nervous system disorders, such as ataxia and head tremors [28, 29].
The Detection of positive samples in the lambs by amplifying the POL and ORF75 tegument protein gene of OvHV-2 in this study corroborates the findings of Li et al. (1998), who reported that OvHV-2 could be transmitted horizontally to lambs in the herd and shed the virus at–5–6 months old [30]. Additionally, Li et al. (2001) indicated that OvHV-2 can infect fetuses during pregnancy [27], as reported by Pekmez et al. [24]. The findings for the virus in different age groups suggest that the virus is endemic to the area, as reported by Mananguit et al. in Philippines [31] and Khudhair in Iraq [14].
Our study indicated a lower prevalence of OvHV-2 in small ruminants than in other reports from Iran and neighboring countries. This discrepancy may be attributed to regional differences, including variations in the climate and husbandry practices. Most livestock farms in Sistan are traditional, with small herd sizes, and mixed farming is prevalent in this area [32]. As a result, susceptible and reservoir hosts of OvHV-2 were kept together in the same husbandry settings. In addition, climate change in the region has led to a decrease in the size of livestock herds [33]. It is important to consider these factors when interpreting our findings as they may contribute to the observed lower prevalence of OvHV-2 in the area. In addition, it should be noted that the sampling area in our study was limited compared to other reports, which may influence our results. In addition, the time interval compared with previous reports in Iran should be noted.
Based on the results of BLAST and phylogenetic analysis, the sequences obtained in this study showed approximately 98–100% similarity to other published sequences of the ORF75 tegument protein gene internationally. These findings support other researchers' findings that there is no major difference between OvHV-2 sequences globally [14, 19, 31].
According to the high similarity with the sequences derived from this study compared to sequences from neighboring countries, specially Pakistan, on the border of the study area, the consequences of legal and illegal movement of livestock within international borders should be considered by authorities. Because of the difference in OvHV-2 prevalence according to reports in different locations, these movements could potentially affect virus circulation.
Sheep-associated malignant catarrhal fever (SA-MCF) is a fatal disease in susceptible hosts such as cattle, buffalo, and deer [6, 34]. The disease causes considerable economic losses owing to the fatality rate and reduction in livestock production [35]. As carrier hosts are considered as dead ends, reservoir hosts, such as sheep and goats, are important for virus circulation [36, 37].
Our study demonstrated OvHV-2 prevalence in sheep and goats, known as the carrier species of the virus, in Sistan in southeast Iran. To the best of our knowledge, this is the first report to indicate OvHV-2 prevalence in sheep and goats and to confirm the presence of the disease in the area by molecular tests. For a better understanding of the disease situation, an investigation of virus prevalence in healthy susceptible animals is required because previous reports have demonstrated that susceptible animals can be infected inappropriately by the virus and play a role as hidden carriers, such as sheep and goats, in the virus circulation.