Genotyping of infectious bursal disease virus strains by restriction fragment length polymorphism analysis of the VP1, VP2, and VP3 genes

Assessing the antigenicity of different VP3 regions of infectious bursal disease virus in chickens from South Brazil

Background

Infectious bursal disease (IBD), also known as Gumboro disease, is a viral infection that causes mortality and immunosuppression in chickens (Gallus gallus). VP2 and VP3 are the major structural viral capsid components and are the most immunogenic proteins of IBD virus (IBDV). Reliable diagnostic tests using VP2 and VP3 produced in heterologous systems are important tools to control this infection. One advantage of an IBD diagnostic based on VP3, over those that use VP2, is that VP3 has linear epitopes, enabling its production in bacteria.

Results

We tested the suitability of recombinant VP3 (rVP3) as a diagnostic reagent in an enzyme-linked immunosorbent assay (ELISA). Compared with a commercial test, rVP3 ELISA showed high sensitivity and specificity as a diagnostic tool for vaccinated animals. In addition, rVP3, but not the commercial ELISA, was able to detect antibodies in nonvaccinated chickens, probably developed against circulating IBDV strains. It was possible the assessment of VP3 regions antigenicity using chicken antisera.

Conclusions

The full-length recombinant VP3 can be used to assess post vaccination immunological status of chickens and its production is feasible and inexpensive. The evaluation of VP3 regions as candidates for general use in the diagnosis of IBD in chickens should be conducted with caution. Our work was the first to identify several regions of VP3 recognized by chicken antibodies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02956-0.

Phylodynamic analyses of Brazilian antigenic variants of infectious bursal disease virus

Infectious bursal disease virus (IBDV) is a very important pathogen to poultry production and it is classified into three main groups: classical virulent (cvIBDV), very virulent (vvIBDV) and antigenic variants (avIBDV). This last group is composed by five different genetic lineages (recently classified in genogroups G2, G4, G5, G6, and G7) distributed in specific regions around the world. Brazil is one of the biggest poultry producers in the world and the present study aimed to investigate the evolutionary history of avIBDVs of the genogroup G4 in Brazil. A total of 5331 IBDV positive bursa samples, from different Brazilian poultry flocks, were genotyped in a period of ten years (2005 to 2014) and 1888 (35.42%) were identified as local avIBDVs. The highly variable region of the viral protein 2 (hvvp2) gene of 28 avIBDVs was sequenced and used in phylogenetic analyses and evaluation of local amino acid signatures. In addition, all complete and partial IBDV vp2 gene sequences, with local and year of collection information available on GenBank, were retrieved. Phylogenetic analyses were carried out based on a maximum likelihood method for the classification of genogroups occurring in Brazil. Based on a Maximum Likelihood (ML) phylogenetic tree, all Brazilian avIBDVs grouped into the genogroup 4. Bayesian phylodynamics analysis demonstrated the ancestor virus of this group was probably introduced in South America in 1968 (1960 to 1974, 95% HPD) and in Brazil in 1974 (1968 to 1977, 95% HPD) and the most likely source was East Europe (Hungary or Poland). All Brazilian avIBDV sequences, as well as the other genogroup 4 sequences, showed a specific pattern of amino acid: S222, T272, P289, I290, and F296. This report brings new insights about the IBDV epidemiology in Brazil and South America.

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

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.

Occurrence of Aviadenovirus in chickens from the poultry industry of Minas Gerais

The occurrence of Aviadenovirus (FAdV) was investigated in chickens from the poultry industry of Minas Gerais state, Brazil. The investigation was conducted due to the scarcity of recent data in the country and its description in neighboring countries. For this purpose, livers were collected from layer chicks (n=25), older layers (n=25), broilers (n=300), and livers (n=25) and stool (n=25) samples from broiler breeders, representing the major poultry regions of the state. FAdV DNA was demonstrated using a previously described PCR protocol for amplifying part of the hexon gene encoding sequence. FAdV was found in layer chicks (36%), widespread (100%) in older layers, and with regional differences in broilers (24-86%). Although all broiler breeder stools were negative, FAdV DNA was detected in livers (16%, 4/25) of stool-negative birds. In order to obtain additional information on the circulation of the infection, livers of subsistence chickens collected from one poultry intensive region, were evaluated (n = 12), with FAdV being detected in all samples. FAdV was found in young and old layers, broilers, broiler breeders and free-range chickens, and results suggest the circulation of FAdV among different types of chickens. The detection in older layer chickens may indicate an extended risk of horizontal transmission in regions of Minas Gerais with mixed activity of egg and meat type chickens and poor biosecurity strategies. The infection in breeders may indicate vertical transmission and the continuous production of infected progenies. The hexon-gene-targeted PCR amplicon sequences aligned with FAdV of species D of Aviadenovirus. Results indicate the necessity for biosecurity, especially for breeders, separating flocks according to origin, age and health status, which will be an advantage regarding any pathogen.

The occurrence of Orthoreovirus, Rotavirus and chicken anemia virus in chickens of the poultry industry in Minas Gerais, Brazil

Fifty-four fecal samples taken from broiler chickens from 1 to 45 days of age, and of pullets from 10 to 13 weeks of age, original from eight different poultry regions in the state of Minas Gerais, Brazil, were collected from March 2008 to January 2010 for avian Orthoreovirus (ARV) and avian Rotavirus (AvRV) analyses. For the assay of ARV, RNA was immediately extracted (Trizolâ) and transcribed into cDNA for assaying in a nested-PCR with ARV-specific primers. For AvRV, polyacrylamide gel electrophoresis (PAGE) was performed with RNA extracts obtained by phenol-chloroform extraction. CAV was additionally investigated through a nested-PCR of thymus and spleen. Results found 5.55% positive for ARV and 9.25% for AvRV. Also, CAV and ARV genomes were detected in co-infection, in a highly prostrated and claudicating chicken flock. No ARV or AvRV infections were detected in pullets. Material of a clinically affected flock was inoculated into SPF embryos, resulting in embryonic hemorrhage, whitish foci in the chorio-allantoic membrane and death. Sequencing of ARV amplicons and isolate cDNA grouped local strains with the ARV S1133 strain, historically used in live vaccines, suggesting the continued circulation of this vaccine virus strain in intensive poultry regions. Detection rates for ARV and AvRV, as well as the presence of CAV, were additionally indicative of failing biosecurity strategies for the intensive poultry regions examined.

Tracking the molecular epidemiology of Brazilian Infectious bursal disease virus (IBDV) isolates

Infectious bursal disease is a highly contagious disease of young chickens caused by Infectious bursal disease virus (IBDV). Genome segment A encodes the capsid protein (VP2), while segment B encodes the RNA-dependent RNA polymerase (VP1). In the present study, we trace the molecular epidemiology of IBDV in Brazil by analyzing 29 isolates collected in the major regions of poultry production. To genetically characterize the isolates, phylogenetic and population dynamic analyses were conducted using 68 VP1 (2634 nt) and 102 VP2 (1356 nt) coding sequences from IBDV isolates from different regions of the world. Furthermore, the evolution of IBDV was analyzed by characterizing the selective forces that operated during the diversification of viral isolates. We show that IBDV isolates were introduced into Brazil mainly from the Netherlands and the USA. These introductions were associated with all Brazilian poultry production regions analyzed in this work. In addition, we show that the evolution of IBDV has been shaped by a combination of very low recombination rates and relatively high rates of nucleotide substitution (2.988×10(-4) for VP1 and 3.2937×10(-4) for VP2), which themselves are a function of purifying selection operating on VP1 and VP2. Furthermore, our extended Bayesian skyline plot suggests that the increase in the effective population size of isolates of IBDV is consistent with its epidemiological history, with a large increase during the emergence of acute outbreaks of IBD in the 1980s.

Molecular characterisation of infectious bursal disease viruses isolated in recent acute outbreaks in Slovenia

In 2004 and then in 2006 several outbreaks of infectious bursal disease (IBD) were reported in broiler and broiler breeder flocks in Slovenia. In this report ten recently emerged IBD viruses (IBDV) were characterised by sequence analysis of the VP2 hypervariable region and compared to previous Slovene IBDV strains from 1995/1996 and to some representative serotype 1 IBDV strains of different pathotypes. On the basis of nucleotide and amino acid identities, phylogenetic analyses and the presence of very virulent IBDV (vvIBDV) conserved amino acid substitutions, all Slovene isolates from recent outbreaks were identified as vvIBDV. Although some unique nucleotide exchanges and amino acid substitutions have been observed, the results of this study indicated that recent vvIBDV isolates are closely related with those from outbreaks in the 1990s. However, acute IBD has not been reported in commercial flocks in Slovenia for some years. This could lead to the conclusion that poor biosecurity and relaxed vaccination could be responsible for the re-emergence of vvIBDV.