Analysis of integrated sequence in an American vaccine of fowl poxvirus

A pair of primers was designed to amplify the integrated sequence of reticuloendotheliosis virus (REV) in the genome of fowl poxvirus (FPV). A 1 478 bp PCR fragment derived from an American poxvirus vaccine was sequenced. The PCR product contained an integrated 193 bp LTR sequence from REV. This integrated sequence that shared 99.6 %, 98.0 %, 87.3 %sequence identity with REV strains APC566, 713, SNV, respectively, but only 83.6 % homology with Chinese strain HA9901. It was exactly same as those identified in other FPV strains AJ581527, AY255633, AF198100, AF006064 and AF246698 including the integ- ration site. This result indicated that the REV sequence integration may have existed in the poxvirus vaccine for a long time.