Direct Evidence for Natural Transmission of Small-Ruminant Lentiviruses of Subtype A4 from Goats to Sheep and Vice Versa

Abstract

Small-ruminant lentiviruses (SRLV), which include the caprine arthritis-encephalitis and the maedi-visna virus, cause persistent inflammatory infections in goats and sheep. SRLV are mainly transmitted from mother to offspring through milk. Transmission after prolonged contact between adult animals has also been observed. The observation that certain SRLV subtypes are found in both goats and sheep suggests that interspecies transmission has occurred on several occasions in the past. We investigated seropositive goats and sheep that were kept together in small mixed herds. Phylogenetic analysis of long proviral sequences in gag and pol, combined with epidemiologic information, demonstrated natural sheep-to-goat transmission of the recently identified SRLV subtype A4 in two instances and goat-to-sheep transmission of the same subtype in one instance. In a further mixed cluster, the direction of the interspecies transmission could not be determined. These findings present for the first time direct evidence that natural interspecies transmission of SRLV is ongoing in both directions. The findings are of relevance to virus eradication programs in both species. (14,17,18,28). Earlier phylogenetic analysis, mostly based on short sequences, has suggested that these very diverse viruses can be divided into six different sequence clades, I to VI (12,21,22,32). Recent work based on long sequences in gag and pol of more than 100 new isolates from Switzerland and all available database sequences has, however, demonstrated that the SRLV should rather be divided into four principal sequence groups A to D, which differ by 25 to 37% in gag and pol sequences. Sequence groups A and B are further divided into different subtypes that differ from each other by 15 to 27%. Group A contains at least 7 subtypes, A1 to A7, and group B contains two subtypes, B1 and B2 (26). To date, subtypes A1 and A2 have been isolated only from sheep, and subtypes A5, A7, and B1 and groups C and D have been isolated only from goats. In contrast, subtypes A3, A4, A6, and B2 have been isolated from both sheep and goats. Caprine arthritis-encephalitis virus (CAEV) and maedivisna virus (MVV) are small-ruminant lentiviruses (SRLV) that infect goats and sheep

Demonstration of Coinfection with and Recombination by Caprine Arthritis-Encephalitis Virus and Maedi-Visna Virus in Naturally Infected Goats

“…Interspecies transmission occurs in the field, as suggested by the detection of some SRLV subtypes in both sheep and goats (16,28,29,38). Recently, direct evidence was found proving that, in mixed flocks of sheep and goats, the SRLV subtypes A4 (32) and B1 (26) do indeed jump the species barrier. In view of these results, we reasoned that double infection may also occur in SRLV-infected goats and sheep.…”

Genetic characterisation of small ruminant lentiviruses in sheep and goats from the Czech Republic

“…The MVV prototypical strains such as strain K1514, EV-1, and SA-OMVV from sheep and the CAEV strain Cork-CAEV isolated from goat (L'Homme et al 2011) were originally viewed as distinct viral species restricted to respective host animal species. As more SRLV sequences had become available for phylogenetic analyses, it became evident that SRLVs can cross the species barrier and can be transmitted from sheep to goats under favourable conditions (Shah et al 2004b;Pisoni et al 2005).…”

Diagnostic Assays Used to Control Small Ruminant Lentiviruses

“…5 In addition, viral strain typing has recently found that some goats contain ovine progressive pneumonia or maedi-like and visnalike viruses and that some sheep contain caprine arthritis encephalitis-like viruses. 12,62,63,66,68,73,74 Furthermore, because sheep and goats often cohabitate, eradication efforts have been focused on eliminating SRLVs in general. Persistently infected animals are a potential reservoir for transmission; therefore, highly specific and sensitive diagnostic tests are required for early detection and separation or culling of both infected sheep and goats.…”