Molecular Analysis of South African Ovine Herpesvirus 2 Strains Based on Selected Glycoprotein and Tegument Genes

Abstract

Ovine herpesvirus 2 (OvHV-2), is the causative agent of sheep-associated malignant catarrhal fever (SA-MCF), a generally fatal disease of cattle and other captive wild ruminants. Information on the OvHV-2 strains circulating in South Africa (SA) and other African countries with regard to genetic structure and diversity, and pattern of distribution is not available. This study aimed to characterize the OvHV-2 strains circulating in SA using selected genes encoding glycoproteins and tegument proteins. To establish the genetic diversity of OvHV-2 strains, four genes, Ov 7, Ov 8 ex2, ORF 27 and ORF 73 were selected for analysis by PCR and DNA sequencing. Nucleotide and amino acid multiple sequence analyses revealed two genotypes for ORF 27 and ORF 73, and three genotypes for Ov 7 and Ov 8 ex2, randomly distributed throughout the regions. Ov 7 and ORF 27 nucleotide sequence analysis revealed variations that distinguished SA genotypes from those of reference OvHV-2 strains. Epitope mapping analysis showed that mutations identified from the investigated genes are not likely to affect the functions of the gene products, particularly those responsible for antibody binding activities associated with B-cell epitopes. Knowledge of the extent of genetic diversity existing among OvHV-2 strains has provided an understanding on the distribution patterns of OvHV-2 strains or genotypes across the regions of South Africa. This can facilitate the management of SA-MCF in SA, in terms of introduction of control measures or safe practices to monitor and control OvHV-2 infection. The products encoded by the Ov 7, Ov 8 ex2 and ORF 27 genes are recommended for evaluation of their coded proteins as possible antigens in the development of an OvHV-2 specific serodiagnostic assay.

Field Observations and Genetic Characterization of Sheep-Associated Malignant Catarrhal Fever in Egypt, 2018

“…Four partial ORF27 coding sequences of 832 bp (missing 50 nucleotides at the 5′ end) were obtained from the PCR-positive samples. No sequence data were obtained with any of the other primer pairs described by Doboro et al [ 14 ]. All 4 ORF27 sequences were identical and distinct from the sequence of the OvHV-2 sample D35/07 used as a positive control for the PCR.…”

“…The OvHV-2 sequences were downloaded, aligned, and trimmed to match the Egyptian sequences. The ORF27 sequence data published by Doboro et al [ 14 ] (5 identical sequences) were extracted from the article and added manually. A maximum-likelihood phylogenetic tree of the 20 ORF27 nucleotide sequences included in this study is shown in Figure 2 .…”

“…Nucleic acid preparations that were positive in the OvHV-2 real-time PCR were used for sequencing using the primers described by Doboro et al [ 14 ]. A 999-bp fragment of the OvHV-2 genome partially overlapping the ORF27 and ORF29 genes [ 24 ] was amplified using the QuantiTect Multiplex PCR NoROX Kit (Qiagen, Hilden, Germany).…”

“…It is important to note that the mucosal lesions of MCF-affected animals are caused by immunopathological processes and not by virus replication [ 12 ]; therefore, the viral load in lesion material and secretions is generally very low [ 13 ]. The amplification of viral DNA from clinical samples by PCR is also necessary for the genetic characterization of circulating strains for epidemiological studies [ 14 ]. Despite reports to the contrary [ 15 ], there currently is no productive cell culture system for OvHV-2 [ 13 ].…”

“…In Europe and North America, MCF is considered to be of minor importance to the cattle industry, and it is a concern mostly in bison, farmed deer, and zoological collections [ 10 ]. Its impact in developing countries, on the other hand, is not well studied and may be considerable depending on herd structure and husbandry practices [ 14 ]. OvHV-2 was previously reported to cause sheep-associated MCF outbreaks in Egyptian cattle and buffalo in 2010 [ 16 ] and 2012/2013 [ 17 ].…”