Detection of proviral DNA in horse cells infected with equine infectious anemia virus.

Equine infectious anemia virus (EIAV) recently has been shown to possess a high-molecular-weight RNA genome and a virion reverse transcriptase. We completed the demonstration that EIAV is a retrovirus by showing the presence of proviral DNA in equine cells infected in vitro, but not in normal horse DNA. These studies were performed by using a highly representative cDNA probe synthesized by the virion polymerase. It was found that this cDNA reassociated extensively, and with high thermal stability, with either viral RNA or DNA extracted from infected cells, but showed no detectable reassociation with DNA from uninfected horse cells. Similarly, sequences related to EIAV were neither found in the DNA of four other Equus species, nor in a variety of other mammals including sheep, cows, pigs- dogs, cats, and humans; nor did EIAV cDNA hybridize with a variety of other retrovirus RNAs. These experiments were performed under conditions of very low stringency to enable detection of distantly related sequences, with a sufficient ratio of DAN to cDNA to allow detection of less than one viral copy per haploid genome. We conclude that EIAV is not an endogenous virus of the horse or of the other species tested.