GENETIC-CHARACTERIZATION OF 2 PHENOTYPICALLY DISTINCT NORTH-AMERICAN OVINE LENTIVIRUSES AND THEIR POSSIBLE ORIGIN FROM CAPRINE ARTHRITIS-ENCEPHALITIS VIRUS

Ovine and caprine lentiviruses are closely related genetically and ant igenically although the diseases that these viruses cause in their res pective host animals can vary greatly. In sheep, syndromes consist pri marily of interstitial pneumonia with rare occurrences of arthritis an d encephalitis, whereas in goats, the disease expresses mainly as arth ritis in adult animals with rare cases of encephalitis in newborns. Ex perimentally, viruses from either sheep or goats can infect animals of the reciprocal species and many field strains of ovine lentivirus hav e biological properties similar to those of caprine viruses. However, a molecular correlation for the phenotypic differences between ovine a nd caprine lentivirus strains is unknown. To investigate this, we exam ined genetic characteristics of two phenotypically distinct North Amer ican ovine lentiviruses. Nucleotide sequence analysis of the envelope regions from virus strains 85/34 and 84/28 showed that despite signifi cant biological differences, these viruses are closely related to each other and are genotypically more homologous to caprine arthritis-ence phalitis virus (CAEV) than to visna virus of sheep. Furthermore, analy sis of the nucleotide substitutions in their env regions indicated tha t when differences between the two ovine viruses and CAEV were found, the changes often resulted in nucleotides homologous with visna virus. These results suggest that the two field strains of ovine lentivirus may have originated from a cross-species infection of sheep by a CAEV- like virus and, evolution of their genomes toward that of ovine lentiv irus may be reflective of adaptation of these viruses to the new ovine host. (C) 1996 Academic Press, Inc.