Very virulent infectious bursal disease virus: reduced pathogenicity in a rare natural segment-B-reassorted isolate.
The purpose of this study was to compare the molecular epidemiology of infectious bursal disease virus (IBDV) segments A and B of 50 natural or vaccine IBDV strains that were isolated or produced between 1972 and 2002 in 17 countries from four continents, with phenotypes ranging from attenuated to very virulent (vv). These strains were subjected to sequence and phylogenetic analysis based on partial sequences of genome segments A and B. Although there is co-evolution of the two genome segments (70 % of strains kept the same genetic relatives in the segment A- and B-defined consensus trees), several strains (26 %) were identified with the incongruence length difference test as exhibiting a significantly different phylogenetic relationship depending on which segment was analysed. This suggested that natural reassortment could have occurred. One of the possible naturally occurring reassortant strains, which exhibited a segment A related to the vvIBDV cluster whereas its segment B was not, was thoroughly sequenced (coding sequence of both segments) and submitted to a standardized experimental characterization of its acute pathogenicity. This strain induced significantly less mortality than typical vvIBDVs; however, the mechanisms for this reduced pathogenicity remain unknown, as no significant difference in the bursal lesions, post-infectious antibody response or virus production in the bursa was observed in challenged chickens.
Nouën
Cyril Le
CL
French Agency for Food Safety (AFSSA), Avian and Rabbit Virology, Immunology and Parasitology Unit, OIE Reference Laboratory for Infectious Bursal Disease, BP 53, 22440 Ploufragan, France.
Rivallan
Gaëlle
G
French Agency for Food Safety (AFSSA), Avian and Rabbit Virology, Immunology and Parasitology Unit, OIE Reference Laboratory for Infectious Bursal Disease, BP 53, 22440 Ploufragan, France.
Toquin
Didier
D
French Agency for Food Safety (AFSSA), Avian and Rabbit Virology, Immunology and Parasitology Unit, OIE Reference Laboratory for Infectious Bursal Disease, BP 53, 22440 Ploufragan, France.
Darlu
Pierre
P
INSERM U535 Genetic Epidemiology and Structure of Human Populations, 94817 Villejuif Cedex, France.
Morin
Yannick
Y
Experimental Services for Avian Pathology (SEEPA), BP 53, 22440 Ploufragan, France.
Beven
Véronique
V
Virus Genetics and Biosecurity Unit, BP 53, 22440 Ploufragan, France.
de Boisseson
Claire
C
Virus Genetics and Biosecurity Unit, BP 53, 22440 Ploufragan, France.
Cazaban
Christophe
C
CEVA-santé animale, BP 126, 33501 Libourne Cedex, France.
Comte
Sylvain
S
CEVA-santé animale, BP 126, 33501 Libourne Cedex, France.
Gardin
Yannick
Y
CEVA-santé animale, BP 126, 33501 Libourne Cedex, France.
Eterradossi
Nicolas
N
French Agency for Food Safety (AFSSA), Avian and Rabbit Virology, Immunology and Parasitology Unit, OIE Reference Laboratory for Infectious Bursal Disease, BP 53, 22440 Ploufragan, France.
D000818:Animals; D018175:Birnaviridae Infections / Q000662:veterinary* / Q000821:virology; D002645:Chickens; D016679:Genome, Viral; D007243:Infectious bursal disease virus / Q000145:classification / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D008969:Molecular Sequence Data; D010802:Phylogeny; D011201:Poultry Diseases / Q000453:epidemiology / Q000821:virology*; D016865:Reassortant Viruses / Q000235:genetics / Q000472:pathogenicity*; D017422:Sequence Analysis, DNA; D014774:Virulence / Q000235:genetics*