Reticuloendotheliosis Virus Sequences within the Genomes of Field Strains of Fowlpox Virus Display Variability

Abstract

Nine field strains of fowlpox virus (FPV) isolated during a 24-year span from geographically diverse outbreaks of fowlpox in the United States were screened for the presence of reticuloendotheliosis virus (REV) sequences in their genomes by PCR. Each isolate appeared to be heterogeneous in that either a nearly intact provirus or just a 248-or 508-nucleotide fusion of portions of the integrated REV 5 and 3 long terminal repeats (LTRs) was exclusively present at the same genomic site. In contrast, four fowlpox vaccines of FPV origin and three originating from pigeonpox virus were genetically homogeneous in having retained only the 248-bp LTR fusion, whereas two other FPV-based vaccines had only the larger one. These remnants of integrated REV presumably arose during homologous recombination at one of the two regions common to both LTRs or during retroviral excision from the FPV genome. Loss of the provirus appeared to be a natural event because the tripartite population could be detected in a field sample (tracheal lesion). Moreover, the provirus was also readily deleted during propagation of FPV in cultured cells, as evidenced by the detection of truncated LTRs after one passage of a plaque-purified FPV recombinant having a "genetically marked" provirus. However, the deletion mutants did not appear to have a substantial replicative advantage in vitro because even after 55 serial passages the original recombinant FPV was still prevalent. As to the in vivo environment, retention of the REV provirus may confer some benefit to FPV for infection of poultry previously vaccinated against fowlpox.

Characterization of reticuloendotheliosis virus isolates obtained from broiler breeders, turkeys, and prairie chickens located in various geographical regions in the United States

“…Embryos and tissue cultures prepared from REV-contaminated embryos may serve as a source of REV contamination of poultry and other vaccines. Accidental contamination of live virus poultry vaccines such as Marek's disease virus and fowlpoxvirus (FPV) with REV (Cook, 1969;Kawamura et al, 1976;Koyama et al, 1976;Yuasa, et al, 1976;Jackson et al, 1977;Fadly et al, 1996b;Fadly & Witter, 1997;Hertig et al, 1997;Garcia et al, 2003;Singh et al, 2003) is an important source of virus infection and can cause runting disease as well as lymphomas in vaccinated chickens, resulting in significant economic consequences.…”

Serological and Virological Surveys of Reticuloendotheliosis in Chickens in Taiwan

“…The primer sequences used were 5'-ATG GAC TKT CTC ACC RAC CTC-3' (Env-F; designed within our laboratory) and 5'-CCT CGA GGC TTG ACC TAG GGT ATC CAT CTC-3' (Ren-R) [19]. The whole env gene was amplified and cloned into yT&A vector (Yeastern Biotech, Taipei, Taiwan).…”

Isolation of Avipoxvirus from Tongue of Canaries (Serinus canaria) Show Severe Localized Proliferative Glossitis

“…The mortality rate is higher in the diphtheritic form than in the cutaneous form, sometimes nearing 50% particularly in young birds. Integration of reticuloendotheliosis virus (REV) sequences has been observed in the genome of fowlpox virus 2003b). It is interesting that this insertion event occurred over 50 years ago (Kim & Tripathy, 2001).…”

“…It is interesting that this insertion event occurred over 50 years ago (Kim & Tripathy, 2001). While most field strains of fowlpox virus contain REV provirus, vaccine strains have only remnants of long terminal repeats (Singh et al, 2003b). Virulence is enhanced by the presence of REV provirus in the genome of field strains of fowlpox virus.…”