Integration of Reticuloendotheliosis Virus in Most of Tanzanian Fowl Pox Virus Isolates is not attributed to Imported Commercial Fowl Pox Vaccines

Abstract

Integration of Reticuloendotheliosis Virus in Most of Tanzanian Fowl Pox Virus Isolates is not attributed to Imported Commercial Fowl Pox Vaccines Aim: To investigate integration of reticuloendotheliosis virus (REV) in the Tanzanian fowlpox virus (FWPV) field isolates, and the imported commercial fowl pox vaccines currently used in the country. Study Design:  Experimental. Place and Duration of Study: Faculty of Veterinary Medicine, Sokoine University of Agriculture, Morogoro, Tanzania; between June 2012 and October 2013. Methodology: Fifty five samples of FWPV isolates from naturally infected chickens, and two isolates of FWPV from samples of the imported commercial fowl pox vaccines were analyzed for integration of REV envelope (env) gene and REV 5'long terminal repeat (5'LTR). The study involved polymerase chain reaction (PCR) amplification of FWPV P4b gene, REV env gene, and REV 5'LTR; agarose gel electrophoresis of PCR products, purification of PCR products, sequencing of the purified PCR products, and sequence analysis using standard procedures.  Results: Out of 55 analyzed field isolates 53 (96.36%) were found to have REV inserts. Most of them [38 (69.09%)] contained both REV env gene and REV 5'LTR inserts, 10 (18.18%) contained inserts of REV env gene only, and 5 (9.09%) contained inserts of REV 5'LTR only. Two isolates (3.64%) were found to be integrated with neither REV env gene nor REV 5'LTR. None of the screened FWPV isolates from the imported commercial vaccines was found to have REV inserts. Sequence analysis revealed that genomic fragments of REV integrated in the Tanzanian FWPV isolate were closely related (99–100% identity) to REV sequences integrated in FWPV isolates from other countries.      Conclusion: Currently there is a heterogeneous population of FWPV in Tanzania comprising of REV-integrated FWPV strains and REV-free FWPV strains. Since strain(s) of REV-integrated FWPV are more virulent than strain(s) of REV-free FWPV, further studies on the REV-integrated Tanzania FWPV isolates aiming at obtaining the appropriate isolate for development of autogenous fowl pox vaccine are highly recommended.