title: Phylogenetic analysis reveals a correlation between the expansion of very virulent infectious bursal disease virus and reassortment of its genome segment B.
abstract: Infectious bursal disease virus (IBDV) is a birnavirus causing immunosuppressive disease in chickens. Emergence of the very virulent form of IBDV (vvIBDV) in the late 1980s dramatically changed the epidemiology of the disease. In this study, we investigated the phylogenetic origins of its genome segments and estimated the time of emergence of their most recent common ancestors. Moreover, with recently developed coalescence techniques, we reconstructed the past population dynamics of vvIBDV and timed the onset of its expansion to the late 1980s. Our analysis suggests that genome segment A of vvIBDV emerged at least 20 years before its expansion, which argues against the hypothesis that mutation of genome segment A is the major contributing factor in the emergence and expansion of vvIBDV. Alternatively, the phylogeny of genome segment B suggests a possible reassortment event estimated to have taken place around the mid-1980s, which seems to coincide with its expansion within approximately 5 years. We therefore hypothesize that the reassortment of genome segment B initiated vvIBDV expansion in the late 1980s, possibly by enhancing the virulence of the virus synergistically with its existing genome segment A. This report reveals the possible mechanisms leading to the emergence and expansion of vvIBDV, which would certainly provide insights into the scope of surveillance and prevention efforts regarding the disease.
authors.affiliation: Department of Zoology, The University of Hong Kong, China.
authors.forename: Chung-Chau
authors.initials: CC
authors.lastname: Hon
authors.forename: Tsan-Yuk
authors.initials: TY
authors.lastname: Lam
authors.forename: Alexei
authors.initials: A
authors.lastname: Drummond
authors.forename: Andrew
authors.initials: A
authors.lastname: Rambaut
authors.forename: Yiu-Fai
authors.initials: YF
authors.lastname: Lee
authors.forename: Chi-Wai
authors.initials: CW
authors.lastname: Yip
authors.forename: Fanya
authors.initials: F
authors.lastname: Zeng
authors.forename: Pui-Yi
authors.initials: PY
authors.lastname: Lam
authors.forename: Patrick T W
authors.initials: PT
authors.lastname: Ng
authors.forename: Frederick C C
authors.initials: FC
authors.lastname: Leung
mesh_terms: D000818:Animals; D018175:Birnaviridae Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D002645:Chickens; D019143:Evolution, Molecular; D016679:Genome, Viral; D007243:Infectious bursal disease virus / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D010802:Phylogeny; D011201:Poultry Diseases / Q000453:epidemiology / Q000821:virology; D016865:Reassortant Viruses / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D013997:Time Factors; D014774:Virulence