Phylogenetic Analysis of Belgian Small Ruminant Lentiviruses Supports Cross Species Virus Transmission and Identifies New Subtype B5 Strains

Small ruminant lentiviruses (SRLV) are a group of highly divergent viruses responsible for global and fatal infections in sheep and goats. Since the current phylogenetic classification of these viruses was proposed in 2004, it nowadays consists out of 5 genotypes and 28 subtypes. In support of our national SRLV control program, we performed the genetic characterization of SRLV strains circulating in the Belgian sheep and goat population. Fourteen sheep and 9 goat strains were sequenced in the gag-pol and pol regions using the method described by Shah. Most SRLV strains from sheep and goats belonged to prototype A1 and B1 subtypes, respectively. We, however, also found indications for cross-species transmission of SRLV strains between sheep and goats and vice versa, and identified a new subtype designated as B5. An in-depth analysis of the current SRLV phylogeny revealed that many subtypes have been defined over the years based on limited sequence information. To keep phylogeny as a useful tool, we advocate to apply more rigorous sequencing standards to ensure the correct classification of current and new emerging strains. The genetic characterization of Belgian SRLV strains will help in the development of appropriate diagnostic tools to assist the national control program.