Conserved sequence motifs involving the tat reading frame of Brazilian caprine lentiviruses indicate affiliations to both caprine arthritis-encephalitis virus and visna-maedi virus

The sequence variation in small ruminant lentiviruses from Brazilian herds of milking goats was sampled in a representative region of the pol gene and in a region including the entire tot open reading frame. Clones were amplified from cDNA derived from virus produced in vitro using primers targetting conserved sequences of the pol gene. Iterative sequencing of clones indicated that animals from two herds in the Minas Gerais area were infected by a caprine arthritis-encephalitis virus (CAEV)-like virus and that individual animals carried variant virus populations. Sequences derived from an infected goat from a herd in Pernambuco showed no nucleic acid variation and were distant from the CAEV-type sequence but marginally closer to ovine visna-maedi virus (VMV) sequences. Sequences amplified from a region including the tot gene, amplified with a common upstream primer within the vif coding region and different downstream primers because of the local divergence between CAEV- and VMV-type sequences, confirmed the affiliation of the Minas Gerais sequences to CAEV and indicated that the Pernambuco isolate was indeed related to VMV, which had not previously been reported to cause natural caprine infection. The overlap between the vif and tot open reading frames clearly distinguished between CAEV-like small ruminant lentiviruses, which shared eight common nucleotides, and the VMV group, where the overlap was reduced to a single base; the final adenine of the vif terminator (TAA) is the initial adenine of the presumptive tot initiator codon. This may be useful for epizoological tracing of the origin of outbreaks.