Pathogenicity, tissue distribution, shedding and environmental detection of two strains of IBDV following infection of chickens at 0 and 14 days of age

Abstract

Infectious bursal disease virus (IBDV) is endemic to most poultry-producing countries worldwide. Immunosuppressive classical and variant IBDV strains endemic to Australia are genetically distinct from other international strains. We report the results of infection experiments with Australian classical strain 06/95 and variant strain 02/95 in SPF chickens. We tested the effects of strain and age of infection on bursal atrophy, viral RNA (vRNA) load in bursa of Fabricius (bursa), spleen, thymus, caecal tonsils, faeces, litter and exhaust dust as determined by real-time reverse transcriptase polymerase chain reaction. The two IBDV strains did not differ in the degree of bursal atrophy induced, lymphoid organ distribution and faecal shedding but variant strain 02/95 induced a greater antibody response to the infection than classical strain 06/95 which was associated with a more rapid decline in IBDV vRNA genome copy number (VCN) in lymphoid organs and faeces. Infection at 14 days of age induced greater bursal atrophy and higher vRNA copy number in lymphoid tissues than infection on the day of hatching, indicating true age susceptibility independent of maternal antibody (Mab) status. The direction of the association between rankings for IBDV vRNA load in bursa and relative bursal weight changed from positive at 3 and 6 days post-infection to negative at 28 days post-infection. Intra-tracheal administration of dust collected from chickens infected with IBDV resulted in successful transmission of IBDV. IBDV vRNA was detected successfully at high levels in the environmental litter and dust samples.

Comparative in vivo pathogenicity study of an ITA genotype isolate (G6) of infectious bursal disease virus

“…Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA-IBDV inoculation. This feature has previously been described for 'variant' IBDV, which has been reported to cause earlier and more severe bursal atrophy than 'classical' strains (Hassan, Al-Natour, Ward, & Saif, 1996;Jayasundara et al, 2017;Sharma et al, 1989).…”

“…Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA‐IBDV inoculation. This feature has previously been described for ‘variant’ IBDV, which has been reported to cause earlier and more severe bursal atrophy than ‘classical’ strains (Hassan, Al‐Natour, Ward, & Saif, ; Jayasundara et al, ; Sharma et al, ). The histopathology scores of the bursa confirmed the aggressiveness of the ITA‐IBDV strain tested in this organ, with scores indicating severe lymphoid depletion, as previously reported by Sharma et al () for the American ‘variant’ strain.…”

“…A significantly earlier antibody response was detected in the ITA‐IBDV group compared with the G1a‐IBDV group. This characteristic was previously considered to be an indicator of high pathogenicity, in the acute phase of IBDV infection, for an Australian variant strain (Jayasundara et al, ). During IBDV infection, it is known that the immune response against the virus itself is not affected; this seems to be a paradox as there is immunosuppression with respect to other antigens.…”

“…in the acute phase of IBDV infection, for an Australian variant strain (Jayasundara et al, 2017). During IBDV infection, it is known that the F I G U R E 3 Histopathology of the bursa of Fabricius and thymus of specific-pathogen-free chickens (×40 magnification, a-c, g-l; ×100 magnification d-f).…”

Tissue distribution, shedding and environmental detection of infectious bursal disease virus genome following infection of meat chickens at two ages

“…These strains are endemic and genetically distinct from overseas classical, variant and vvIBDV strains . In vivo studies have confirmed the immunosuppressive effects of infection with the Australian classical and variant strains …”