Recombinant avian leukosis viruses of subgroup J isolated from field infected commercial layer chickens with hemangioma and myeloid leukosis possess an insertion in the E element

Abstract

BackgroundFive isolates (JS09GY2, JS09GY3, JS09GY4, JS09GY5, and JS09GY6) of avian leukosis virus subgroup J (ALV-J) were isolated from six infected commercial layer flocks displaying both hemangioma and myeloid leukosis (ML), which shared the same parental line, in China in 2009.ResultsAll six of the commercial layer chickens examined showed hemangiomas on their body surface or feet. Some developed hemangiomas in their internal organs, causing hepatorrhexis and blood loss. Histopathologically different stages of hemangiomas with ML in the liver, heart, and spleen, were observed. Five viral isolates were obtained from infected DF1 cells incubated with the spleen tissue or serum of the birds from the six flocks. By full genome sequences analysis, a 19-nucleotide repeat sequence was identified in the primer binding site (PBS)-leader region of isolates JS09GY3 and JS09GY6, located between sites 249 and 250 according to the sequence of reference strain HPRS103, and also present in Rous sarcoma virus strain Schmidt–Ruppin B (RSV-SRB), Rous associated virus type 1 (RAV-1), and Rous associated virus type 2 (RAV-2). The predicted Gp85 proteins of isolates JS09GY2, JS09GY3, JS09GY5, and JS09GY6 were highly variable. Interestingly, the E elements of these four examined isolates showed a key deletion at site 30, which produced a new c-Ets-1 binding site. An 11-bp insertion was also found in the E element of isolate JS09GY3 located between bp 66 and 67 according to the sequence of reference strain HPRS103, while almost all previously reported Chinese strains showed an almost identical deletion of 127 bp in the same region.ConclusionsFive ALV-J isolates were obtained from six field infected commercial layer chickens. Coexistence of hemangioma and ML were observed in these infected cases both macro- and microscopically. Complete proviral genome sequences of two isolates (JS09GY3 and JS09GY6) and the partial sequences of the other two isolates (JS09GY2 and JS09GY5) were determined. The isolates were found to be recombinants of ALV-J with a PBS-leader sequence originating from other retroviruses. The Gp85 protein with an amino acid deletion, a contiguous 11-bp insertion mutation in the E element, and a novel binding site, were noted in the proviral genomes.

An avian leukosis virus subgroup J isolate with a Rous sarcoma virus-like 5′-LTR shows enhanced replication capability

“…In addition, sequence changes in the U3 region have been implicated in both the level of viral transcription and the oncogenic potential of ALVs (Cullen et al, 1985;Ryden et al, 1993). A comparison of the U3 sequences in ALV-J broiler strains and layer isolates indicated that the U3 region of ALV-J layer isolates has evolved rapidly (Hue et al, 2006;Gao et al, 2012;Wu et al, 2010). The results of this study suggested that the stronger enhancer activity of the U3 region that was substituted from RSV resulted in a faster replication rate of the recombinant ALV-J strain.…”

“…Recombination has been observed between exogenous viruses, between exogenous and endogenous viruses, and between exogenous virus and nonhomologous cellular genes, e.g. a strain of ALV-J with a primer-binding site leader sequence that originated from other retroviruses (Wu et al, 2010), a naturally occurring recombinant ALV-B strain with a subgroup J-like longterminal repeat (Gingerich et al, 2002;Lupiani et al, 2006), a recombinant that was composed of most of the ALV-J genome and part of the corresponding env sequence of ALV-E , and a recombinant ALV with ALV-A gp85 and the ALV-E LTR, which originated from contaminated Marek's disease vaccines (Barbosa et al, 2008).…”

Molecular Epidemiology of Avian Leukosis Virus Subgroup J in Layer Flocks in China

“…Although an intact E element was not a critical requirement for the ALV-J induction of tumors, the presence of the E element could be associated with a higher frequency of tumors in susceptible chickens (8). The ALV-Js isolated from layer flocks induced a high incidence of hemangioma in China (6,36). However, previous studies indicated that the dominant tumor induced by ALV-J infection in meat-type chickens was a myelocytoma (ML) (21).…”

“…However, field cases of ALV-J infection and tumors in commercial layer chickens emerged in 2004 (37). ALV-J has been found to induce various tumors and cause significant economic losses in parent and commercial layer flocks in recent years, especially from 2008 to 2010 (6,14,18,36). Many field cases of ALV-J infection and tumors occurred in 15-to 29-week-old egg-type chickens in several provinces.…”

“…Although several field cases and complete proviral genomic sequences for ALV-J strains isolated from layer chickens have been reported (6,18,36), little is known about the molecular epidemiology of ALV-J layer isolates in China. The first study conducted by our laboratory between 2007 and 2009 showed that ALV-J is predominantly responsible for layer avian leukosis in China (14).…”