Previous molecular analyses of small ruminant lentivirus (SRLV) populations in single species herds in
Quebec, Canada, have revealed a relatively simple structure where goats and sheep appeared exclusively
infected with B1 and A2 subtypes respectively. The present work aimed at extending these earlier findings
with the analysis of SRLVs in mixed flocks. Molecular analyses revealed a more complex picture of
SRLV population structure in mixed herds compared to single species herds. Notably, phylogenetic analyses
of long gag sequences strongly support transmission of A2 subtype from sheep to goats as well as
transmission of B1 subtype from goats to sheep. Hence, this work uncovered for the first time natural
transmission between sheep and goats of North American subtype A2. In addition, multiple evidences
of mixed infection of sheep and goats with A2 and B1 subtypes were found. The data reported in this
study reinforces the concept of a genetic continuum of SRLVs where strains are exchanged between sheep
and goats under favourable conditions and in the absence of specific species barriers. Most interestingly,
this study suggests that dual infection, which is a hallmark of the lentivirus paradigm HIV, may not be
such rare events in small ruminants but may simply be understudied and underreported. Overall, the
present data shows that sheep and goats in Canada can be infected with both SRLV A and B types, sometimes
simultaneously, and that mixed flocks may represent a breeding ground for their evolution.