Field and Vaccine Strains of Fowlpox Virus Carry Integrated Sequences from the Avian Retrovirus, Reticuloendotheliosis Virus

Abstract

For baculoviruses and herpesviruses, integration of transposons or retroviruses into the virus genome has been documented. We report here that field and vaccine strains of fowlpox virus (FPV) carry integrated sequences from the avian retrovirus, reticuloendotheliosis virus (REV). Using PCR and hybridization analysis we observed that vaccine and field strains of FPV carry REV sequences integrated into a previously uncharacterized region of the right 1/3 of the FPV genome. Long-range PCR, hybridization, and nucleotide sequence determination demonstrated that one vaccine strain (FPV S) and recently isolated field strains carry a near-full-length REV provirus. For another vaccine strain (FPV M) a rearranged remnant of the LTR was found at the same insertion site. By Western blotting and reverse transcriptase assays we were unable to demonstrate free REV in supernatants of FPV S cultures. The near-full-length REV provirus integrated into the FPV genome is infectious since FPV S DNA gave rise to REV upon transfection into chicken embryo fibroblasts. Upon infection of chickens with FPV S, all chickens developed high-titered antibodies to REV, and REV was isolated from the blood of half of the inoculated chickens. Our observations add to the list of targets for retrovirus integration into DNA virus genomes. The integration of a near-full-length, and apparently infectious, REV provirus into FPV provides additional transmission routes for the retrovirus by way of the infectious cycle of FPV, including the possibility of mechanical transmission by biting insects since FPV is believed to be transmitted by this route. For large DNA viruses, including the poxviruses, retrovirus integration with attendant possibilities of gene transduction may be an important mechanism for virus evolution, including the acquisition of cellular genes with the potential to modify virus virulence and pathogenicity.

Insertion of reticuloendotheliosis virus long terminal repeat into a bacterial artificial chromosome clone of a very virulent Marek's disease virus alters its pathogenicity

“…Previously published reports indicate dual or coinfections of herpesvirus and retrovirus can occur within a single host (Pietroboni et al, 1988;Heng et al, 1994;Davidson et al, 2002), resulting in insertion of retrovirus sequences into the genome of herpesvirus (Isfort et al, 1992(Isfort et al, , 1994bKost et al, 1993;Sakaguchi et al, 1997). Recombination occurs both in vitro following co-infection of cell culture and naturally in vivo following mixed infection of avian species with DNA and RNA viruses.…”

“…Recombination occurs both in vitro following co-infection of cell culture and naturally in vivo following mixed infection of avian species with DNA and RNA viruses. Integration of a REV long terminal repeat (LTR) into fowlpoxvirus in avian species demonstrated that natural recombination occurs in nature and can lead to unexpected changes in the retroviral spread pattern and pathogenicity of the resultant recombinant virus (Hertig et al, 1997). Furthermore, beginning in 1993, an extensive survey of Israeli commercial flocks evaluated the incidence and the prevalence of flocks and birds with multiple viral infections (Davidson et al, 1995;Davidson & Borenshtain, 2001).…”

“…REV readily integrates into the genome of virulent type I MDV following both long-term and short-term co-infection of chicken or duck embryo fibroblasts (Isfort et al, 1992;Jones et al, 1993). A complete LTR was inserted into the MDV IR s region of the MDV strain, JM/102 W, upon co-cultivation with the REV strain, chick syncytial virus, in duck embryo fibroblast (DEF) cultures.…”

“…A complete LTR was inserted into the MDV IR s region of the MDV strain, JM/102 W, upon co-cultivation with the REV strain, chick syncytial virus, in duck embryo fibroblast (DEF) cultures. The original LTR-containing virus, RM1, was isolated from a 15I 5 )7 1 chicken inoculated with a suspension of DEF co-infected with MDV JM/ 102W (JM) and the chick syncytial virus and was passed a total of 14 times (Isfort et al, 1992). Cell-free virus was isolated from feather follicles following inoculation of chickens with passed RM1 virus and the clone, RM1, was selected for further analysis and characterization following plaque purification (Jones et al, 1996).…”

Reticuloendotheliosis in Hungarian Partridge

“…Transmission of REV via contaminated fowlpox vaccines has been documented in turkeys and chickens (Fadly et al, 1996;Fadley and Witter, 1997). Field and vaccine strains of fowlpox viruses from Australia, Europe, and the United States have been shown to carry sequences of the REV genome integrated into the fowlpox virus DNA (Hertig et al, 1997). Some pox viruses carry near full-length REV provirus sequences which can generate fully infectious virions when the contaminated pox virus is injected into susceptible chickens.…”