Characterization of field infectious bursal disease viruses in Zambia: evidence of co-circulation of multiple genotypes with predominance of very virulent strains

Abstract

Infectious bursal disease (IBD) is a highly contagious, immunosuppressive disease of chickens and causes substantial economic losses to the poultry industry globally. This study investigated the genetic characteristics and pathological lesions induced by IBD viruses (IBDVs) that were associated with 60 suspected outbreaks in chickens during 2015-2016 in Lusaka Province, Zambia. Nucleotide sequences of VP2 hypervariable region (VP2-HVR) (n = 38) and part of VP1 (n = 37) of Zambian IBDVs were phylogenetically analysed. Phylogenetic analysis of the VP2-HVR and VP1 revealed that most viruses (n = 31 of each genome segment) clustered with the very virulent (vv) strains. The rest of the viruses clustered with the classical strains, with two of the viruses being closely related to attenuated vaccine isolates. Two of the viruses that belonged to the vv genotype had a unique amino acid (aa) substitution Q324L whereas one virus had two unique changes, N280S and E300A in the VP2-HVR aa sequence. Although Zambian strains with a vv genotype possessed virulence marker aa within VP1 at 145T, 146D and 147N, two viruses showed unique substitutions, with one virus having 147T while the other had 147H. Pathologically, it was noted that only viruses with a vv genotype appeared to be associated with inducing pathological lesions in non-lymphoid organs (proventriculus and gizzard). Whilst documenting for the first time the presence of classical virulent IBDVs, this study demonstrates the involvement of multiple genotypes, with predominance of vvIBDVs in the epidemiology of IBD in Zambia.

Epidemiological Occurrence of the Infectious Bursal Disease Virus in Chickens’ Flocks that Had Received Various Vaccination Regimens

“…In the present study, the high stocking density increased the detection of IBDV as recorded before [33]. The common ages of the studied IBD flocks in most of the previous researches were ranged from 3-6 weeks [43,44]. Likewise, our results exhibited that 91.7% (11/12) of the investigated chicken flocks were from flocks aged >35 days.…”

Phylogenotyping of the Vietnamese infectious bursal disease viruses according to the newly unified genotypic classification scheme

“…The possibility of such reassortment to result in isolates with segment A from the "very virulent" (A3) and segment B derived from the classically attenuated IBDVs (B3) (or vaccines, i.e., from the 002-73 Australian strain) [54] has been well documented, and this co-evolution occurred due to the co-existence of the virulent and attenuated vaccine strains in the eld [20,37,[55][56][57]. Why the A3B3 reassortants have become so virulent and widely spread worldwide, and how the B3 (the early Australian-like B segment) was reassorted with the A3 segment, is a question for further investigation.…”

Outbreaks of acute infectious bursal disease of chickens in Maiduguri, Nigeria (2008-2018): retrospective survey

“…Presumptive or tentative postmortem diagnosis of acute IBD, based on clinical signs and postmortem lesions (Teshome and Admassu, 2015;Mwenda et al, 2018), is made by veterinarians after examination of dead or moribund chickens submitted during disease outbreak and the records of diagnosed diseases become useful in epidemiological monitoring of spatial and temporal trends during disease surveillance (Igbokwe, 1989). Lack of data on nationwide prevalence of IBD outbreaks in Nigeria has undermined evidence-based assessment of the disease burden and effectiveness of control measures adopted against the disease.…”

“…with subsequent positive laboratory diagnosis by molecular techniques in several reported clinical outbreaks; and the BF of chickens showing typical gross lesions yielded amplicons of IBDV in 100% of clinical outbreaks(Owolodun et al, 2015;Nwagbo et al, 2018;Arowolo et al, 2021;Omer et al, 2022).When the BF from a tentative clinical outbreak was not positive for IBDV in molecular diagnosis, it was presumed that the molecular technique was not sensitive to amplify the virus genome because of genomic mutation, reassortment and recombinations of the eld virus strain(Mwenda et al, 2018). Acute IBD is the only known disease of chickens that causes grossly visible acute exudative in ammatory swelling of the BF with hemorrhage.…”