Characteristics of a Very Virulent Infectious Bursal Disease Virus from California

Abstract

An outbreak of infectious bursal disease (IBD) in two California layer flocks resulted in the isolation of two infectious bursal disease viruses designated rA and rB. Increased mortality plus gross and histopathology in the layer flocks suggested rA and rB could be very virulent infectious bursal disease virus (vvIBDV). Preliminary studies indicated that high mortality resulted when bursa homogenates from the layer farms were used to inoculate specific-pathogen-free (SPF) chicks. In addition, rA and rB contained VP2 amino acid sequences typically seen in vvIBDV. Molecular and in vivo studies were conducted to more thoroughly identify and characterize the rA and rB viruses. Nucleotide sequence analysis demonstrated that rA and rB had identical sequences across the hypervariable VP2 (hvVP2) and segment B regions examined, and their amino acid sequences in the hvVP2 region were identical to the vvwIBDV type strains UK 661, OKYM, and Harbin. Furthermore, the genome segment B nucleotide sequences examined for rA and rB were a 98.1% match with vvIBDV and only an 88.0% match with classic IBDV strains. Phylogenetic analysis placed the rA and rB viruses with other vvIBDV and confirmed these viruses were close genetic descendants of vvIBDV seen around the world. Pathogenicity studies in 4-wk-old SPF chicks demonstrated that at a high dose (105.5 50% egg infective dose [EID50]) and a low dose (102.0 EID50) of rA and rB, mortality ranged from 91% to 100%. A pathogenic classic virus, standard challenge (STC), at similar doses did not cause mortality in the SPF chicks. In addition, mortality occurred in three out of four SPF birds exposed by direct contact to rA and rB inoculated chicks. Serum from convalescent birds inoculated with rA had high titers to IBDV but were negative for antibodies to infectious bronchitis virus, avian influenza virus, chicken anemia virus, Newcastle disease virus, Mycoplasma gallisepticum, and Mycoplasma synoviae. Virus isolation attempts on the rA and rB bursa homogenate inocula also indicated that no contaminating microorganisms contributed to the high mortality and pathology observed in the SPF chicks. In one experiment, broilers with maternal immunity to IBDV were protected from infection and disease when they were challenged with 10(2) EID50 and 10(5) EID50 of the STC virus. When challenged with 10(2) EID50 of the rA virus, the maternally immune broilers were protected from disease but not infection as evidenced by a positive reverse transcription-polymerase chain reaction (RT-PCR) assay for the virus. When the broilers were challenged with 10(5) EID50 of the rA virus, they had typical gross and histopathologic signs of IBD but no mortality by 7 days postinoculation. It was concluded that the rA and rB viruses meet the genotypic and phenotypic characteristics of a vvIBDV.

Molecular characterization of field infectious bursal disease virus isolates from Nigeria

“…The double-stranded RNA was denatured at 95°C for 5 min before RT-PCR was performed with an AgPath-ID™ One-Step RT-PCR kit (Ambion; Applied Biosystems, Foster City, CA) according to manufacturer’s instructions. Primers 743-F: 5´-GCCCAGAGTCTACACCAT-3´ and 743-R: 5´-CCCGGATTATGTCTTTGA-3´ [23] were used to amplify the hvVP2 region of genome segment A and primers B-168AF (5´-CATAAAGCCTACAGCTGGAC-3´) and B-889R (5´-GTCCACTTGATGACTTGAGG-3´) [24], were used to amplify a portion of VP1. For segment A, RT was performed at 48°C for 30 min and then inactivated at 95°C for 10 min followed by 35 cycles at 95°C for 30 s and 57°C for 90 s. After completion of the 35 cycles, a final extension at 72°C for 5 min was performed.…”

Pathogenicity associated with coinfection with very virulent infectious bursal disease and Infectious bursal disease virus strains endemic in the United States

“…17 The SPF chickens were divided into 5 challenge groups (1a-e) and 1 uninoculated negative control group, 1f (Table 1). Five birds were allotted to each group except for positive control group 1e, which consisted of 10 birds (Table 1).…”

Evaluation of the Protection against Infectious Bursal Disease (IBD) Challenge in Progeny Born to Parents Having Received a Vaccination Program Using a Herpesvirus of Turkey-Infectious Bursal Disease (HVT-IBD) Vector Vaccine

“…Vaccination strategy is dual: passive protection induced by the maternally-derived antibodies (MDA) and active immunization of the progeny by its vaccination [2,3], taking into account the interference between these MDAs and the live vaccine take. A very virulent form of the disease was described around twenty years ago [4,5] and is still considered as a major treat to the poultry industry everywhere in the world [6], and more recently in the United States of America [7]. Very virulent (vv) IBD infections lead to severe clinical signs of IBD and high mortality.…”