Abstract
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.
Highlights
Maedi-Visna virus (MVV) and caprine arthritis encephalitis virus (CAEV), referred to as small ruminant lentiviruses (SRLV), are two related retroviruses infecting sheep and goats [1,2].They are both responsible for a persistent and lifelong infection by targeting the monocytes of the host and the stem cells located in the bone marrow [2]
The basis of the current classification of SRLV strains was proposed in 2004 by Shah et al using the genetic sequence of a 1.8 kb fragment in the gag-pol region, a 1.2 kb fragment in the pol region, and a smaller fragment (279 bp) within the reverse transcriptase (RT) region
The current SRLV phylogeny consisting of 5 genotypes, which are further divided in multiple subtypes, emphasizes the high genetic variation that exists among SRLV strains
Summary
Maedi-Visna virus (MVV) and caprine arthritis encephalitis virus (CAEV), referred to as small ruminant lentiviruses (SRLV), are two related retroviruses infecting sheep and goats [1,2].They are both responsible for a persistent and lifelong infection by targeting the monocytes of the host and the stem cells located in the bone marrow [2]. SRLV are mainly transmitted vertically to newborns via the ingestion of infected milk and colostrum and horizontal transmission can occur at any age via the inhalation of viral particles between animals housed in close contact [5,6]. The incidence of these infections causes considerable economical losses in animal production and no therapy or vaccine is currently available [7]
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