Molecular detection and characterization of malignant catarrhal fever viruses in Namibia: insights into OvHV-2 and AlHV-1 presence at the wildlife–livestock interface

Abstract Malignant catarrhal fever (MCF) is a severe lymphoproliferative disease of domestic and wild ruminants caused by macaviruses, mainly ovine gammaherpesvirus 2 (OvHV-2) and alcelaphine gammaherpesvirus 1 (AlHV-1). Although relevant in sub-Saharan Africa, molecular epidemiological data remain limited, particularly in Namibia. This study investigated the occurrence and diversity of MCF viruses in Namibian livestock and contextualised local strains globally. Fifteen samples from cattle and sheep suspected of MCF were collected across five Namibian regions in 2023. Viral DNA was screened by duplex nested PCR, followed by amplification and sequencing of selected OvHV-2 (ORF50, ORF75, Ov9.5) and AlHV-1 (ORF50, A9.5) genomic regions. Phylogenetic and genetic distance analyses assessed viral diversity. OvHV-2 was the most commonly reported, being detected in 13/15 samples from both symptomatic cattle and asymptomatic sheep, whereas AlHV-1 was identified in two bovine cases. OvHV-2 sequences showed limited diversity and clustered into two main clades, without clear geographic structuring and with intermixing between host species. Several Namibian strains were closely related to sequences from Africa, Europe, Asia, and North America, depending on the genomic region analysed. AlHV-1 sequences were related to strains from southern and eastern Africa. These findings support widespread OvHV-2 circulation and indicate sheep as a likely infection source for cattle. The lack of spatial structure and presence of multiple clades suggest complex transmission dynamics, potentially influenced by animal movements, although the role of livestock trade and wildlife-mediated transmission remains unclear. Enhanced molecular surveillance, biosecurity, and control of animal translocations are needed to mitigate MCF impact in the region.