In vivo replicative status and envelope heterogeneity of equine infectious anemia virus in an inapparent carrier

The distribution and replicative status of equine infectious anemia virus (EIAV) DNA in the tissues of a well-characterized inapparent carrier horse were established by using the PCR technique. The EIAV pol region could be amplified in all of the tissues tested, including the cerebellum and periventricular tissue, at concentrations approximately 10(5)-fold less than in the same tissue from an acutely infected horse. Further analysis of the EIAV genome, with primer pairs diagnostic for sequential stages of reverse transcription, suggests that EIAV DNA in the brain, liver, and lymph nodes was incompletely synthesized. The products of reverse transcription were found to diminish progressively during first-strand synthesis, while products indicative of second-strand synthesis were observed only in kidney and spleen DNA samples. Sequences specific for different regions of the envelope could not be amplified from any of the tissues of the inapparent carrier, suggesting that the envelope is highly variable and may be subject to extensive drift. Together, the data suggest that low levels of EIAV replication persist without causing clinical disease in an inapparent carrier.