Molecular Evolution And Recombination Analysis Of Marek’s Disease Viruses Prevalent In Chicken Flocks In Henan Province During 2011-2014

Marek’s disease virus(MDV) is one of the few oncogenic herpesviruses that can induce tumors in their natural hosts, namely Marek’s disease(MD), which is the first effective use of antiviral vaccines to prevent a naturally occurring cancer. To investigate the molecular characteristics of MDV prevalent in chicken flocks in Henan province, liver tissues were sampled from the suspecious cases in the flocks suffered from MD during the year 2012-2014. We amplified the MDV 132-bp repeat from these tissues by the polymerase chain reaction(PCR) and simultaneously, the meq, g E and g I genes were amplified, cloned, sequenced and then compared with the reference MDV strains and/or isolates. The main amplicons of the 132-bp repeat PCR products are the same size as 2 copies of the 132-bp repeats, similar to that of the positive GX0101 control. The sequences of meq, g E and g I genes cloned from clinical tissues are relatively conserved, with the homology among 98.5%~100%, 98.8%~100% and 98.0%~100% respectively compared to the reference MDV isolates and/or strains. Based on the sequences of meq, g E and g I genes, the phylogenetic analysis were performed and showed that compared to the strains or isolates from USA, Australia, Japan and India, the MDVs prevalent recently in Henan province were evolutionarily clearly more adjacent to the previously reported Henan MDV isolates. Together with the isolates from the other regions in China, the Chinese isolates form an independent branch in the phylogenetic tree. This study provides more detailed information regarding the field MDVs circulating in Henan province and may be meaningful for the further control of MD.Like MDV, reticuloendotheliosis virus(REV) is also one of the most important pathogens that cause the immunosuppressive and neoplastic disease of poultry. Sharing the similar tissue tropism, co-infections of both MDV and REV in chicken flocks have led huge economic losses for poultry industry. Previous studies have shown that the REV provirus can naturally or artificially integrate into the genome of MDV, which may significantly affect the pathogenic properties of MDV. In order to evaluate the status of the natural integrations of REV into the MDV field isolates prevalent in China, we presently investigated 17 MDV isolates obtained from the vaccinated chicken flocks distributed in different regions in Henan province. Our results showed that, among the 17 Henan isolates, two isolates, HNGS206 and HNXZ103, are recombinant MDVs containing the REV LTR inserts. Further studies showed that neither of the two isolates are natural recombinant viruses and the integrations of LTR into the viral genomes may result from the clinical co-infection and/or virus isolation procedure. Our study suggests that a wide-spread co-infection of the two viruses possibly exists in the chicken flocks in Henan province, but the prevalence of the naturally occurring MDV recombinants needs to be further monitored.