Type‐specific antigenicity of avian reoviruses

Veterinary Autogenous Vaccines for Poultry in Europe-Many Ways to Crack an Egg

In the past decade, European animal farming has increasingly used autogenous vaccines for the prevention of nonnotifiable diseases. In Europe, these vaccines are exclusively inactivated bacterial and viral vaccines, with a set of specific regulations that differentiate them from conventional vaccines. The highest number of applications most likely occurs in poultry, as these animal species are farmed in the highest numbers compared with other types of food-producing animals. In 2019, autogenous vaccines came within the scope of harmonized European regulation for the first time, although many important aspects are still missing and need to be further developed. Consequently, several important legal provisions remain in national legislations and can vary tremendously between different member states of the European Union. The inclusion of autogenous vaccines in the management of certain diseases of poultry is justified by the nonavailability of licensed vaccines and the evolution and diversity of antigens in the field that are not covered by licensed vaccines. In addition, these vaccines aid in reducing the use of antibiotics. The methods for isolating and typing pathogenic isolates to obtain relevant antigens are pathogen specific and require a careful approach based on clinical evidence. Manufacturing processes are optimized according to regulatory standards, and they represent the most critical factor influencing the quality of autogenous vaccines and their placement on the market. This review presents the important requirements for manufacturing autogenous vaccines for poultry in addition to the relevant regulatory considerations. The results from a survey of several European Union member states regarding specific provisions within their national legislations are also presented.

Development of a multivalent adjuvanted inactivated vaccine against variant arthrotropic avian reoviruses

Variant avian reoviruses (ARVs) are economically important emerging pathogens of poultry, which mainly affect young broiler chickens and cause significant production losses. Currently, there are no effective commercial vaccines available for control and prevention of emerging variant ARVs. In this study, monovalent inactivated adjuvated (20% Emulsigen D) broiler breeder vaccines containing antigens from ARV genotype cluster (C) group -2, -4, -5, or -6, and a multivalent vaccine containing antigens from all the four indicated genotypic cluster groups were developed and evaluated for their efficacy in protecting broiler progenies against homologous or heterologous ARV challenge. The use of monovalent or multivalent inactivated vaccines in a prime-boost immunization strategy induced the production of ARV specific antibodies in broiler breeders. The maternal antibodies were effectively transferred to broiler progenies. Broiler progenies obtained from immunized breeders demonstrated milder clinical symptoms and reduced gross and histopathological lesions after homologous ARV challenge. More severe gross and histological lesions were observed in challenged progenies from unvaccinated broiler breeders. However, cross protection was not observed when either of the monovalent-vaccine groups were challenged with a heterologous virus. In addition, the progenies from the unvaccinated ARV challenged control or heterologous ARV challenged vaccinated groups had significantly reduced body weight gain (p < 0.01) than the unchallenged-control, challenged-multivalent, or homologous ARV-challenged monovalent vaccine groups. However, homologous ARV challenged progenies in the multivalent or monovalent vaccine groups had similar body weight gain as the control unchallenged group with significantly reduced viral load (p < 0.01) in the gastrocnemius tendon tissue. This study indicates that broad-spectrum protection of broiler progenies from variant ARV infections is feasible through the development of multivalent vaccines after proper characterization, selection and incorporation of multiple antigens based on circulating ARV genotypes in targeted regions.

A Novel Variant of Avian Reovirus Is Pathogenic to Vaccinated Chickens

Avian reovirus (ARV) infections, characterized by severe arthritis, tenosynovitis, pericarditis, and poor weight gain, have become increasingly serious in recent years. The economic impact is significant as it causes growth inhibition and immunosuppression. Some commercial poultry in China have been widely vaccinated with available ARV vaccines; however, infections continue to occur even after vaccination. This study aimed to isolate a novel variant, ARV-SD19/11103, from the joint tissues of infected broiler chickens vaccinated with ARV vaccines in Shandong Province. Genetic evolution analysis of the major protective antigen σC gene in ARVs showed that ARV-SD19/11103 was located in the genotype cluster I but not in the same sub-cluster as the S1133 vaccine strain. The amino acid sequence similarity between SD19/11103 and vaccine strains S1133, 1733, and 2408 was <80%. After analyzing the amino acid sequences of the σC protein, 33 amino acid differences were found between the new variant isolate and the vaccine strains. This novel variant showed obvious pathogenicity in specific pathogen-free chicken embryos and chicks and could cause serious disease in chickens vaccinated with commercially available ARV vaccines. Cross-neutralization experiments further demonstrated a significant antigenic difference between the novel variant and genotype cluster I ARV strains. The novel variant strain isolated in this study provides an important theoretical basis for understanding the prevalence and genetic evolutionary characteristics of ARV variant strains in our country. This study identified the causes of ARVs circulating and emphasizes the needs for developing new vaccines against novel ARV variants.

First Seroprevalence Survey of Avian Reovirus in Broiler Breeders Chicken Flocks in Morocco

Avian reovirus (ARV) is a prevalent infectious agent that has the potential to cause respiratory and gastrointestinal illnesses in poultry, leading to substantial financial losses in the poultry sector. Until now, there have been no investigations conducted to examine the epidemiological status of ARV infections in Morocco. The aim of this study was to investigate the seroprevalence of ARV infections with respect to area, types of chickens (broiler breeder, and broiler), vaccination status, and age of chickens. A total of 826 serum samples were collected from 36 broiler and broiler breeder flocks, with 14 of them being unvaccinated, fromsix different regions of Morocco, namely Casablanca-Settat, Rabat-Salé-Kénitra, Tanger-Tétouan-Al Hoceïma, Oriental, Marrakech-Safi, and Fez-Meknès between 2021 and 2022.These serum samples were screened using a commercial indirect ELISA ARV antibody test kit (IDEXX REO). The study found that all tested flocks were positive for ARV-specific antibodies, indicating that the virus was present in these flocks. Out of the 826 serum samples tested, 782 were positive for ARV-specific antibodies. The overall prevalence of ARV infections in breeder and broiler flocks was calculated to be 94.6% ± 0.78. To summarize, the current study provides evidence of the widespread distribution of ARV infections in Morocco, suggesting that the poultry industry in the country is highly infected with ARV.

First report of seroprevalence and genetic characterization of avian orthoreovirus in Egypt

Recently, the Egyptian broiler industry has experienced an increased incidence of avian reovirus (ARV) infections. However, to date, no studies have been carried out to investigate the epidemiologic status of ARV infections as well as the genetic characteristics of the currently circulating ARV strains. The present study estimates the seroprevalence of ARV infections in Alexandria, El-Behera, Giza, Kafr El-Sheikh, and Gharbia governorates, Egypt, during the period 2017-2018. A total of 150 serum samples from 15 unvaccinated broiler flocks with suspicious ARV infection were screened using a commercial enzyme-linked immunosorbent assay kit. All the tested flocks were found to be positive for ARV-specific antibodies, and the overall seropositivity rate was 80.6%. Meanwhile, 5 (33.3%) flocks were confirmed for the presence of ARV through a reverse transcription-polymerase chain reaction (RT-PCR) assay based on the σA-encoding gene. Phylogenetic analysis based on the nucleotide sequences of the σA-encoding gene revealed that the obtained ARV isolate, designated EGY1, was grouped in the S1113-like cluster of ARV and displayed 100% and 98.7% nucleotide identity with the Chinese MSO1 isolate and the S1133 vaccine strain, respectively. In addition, amino acid alignments with the S1133 vaccine strain revealed that the σA protein of the EGY1 isolate carried the substitutions G81S and A118V. In conclusion, the present study provides the evidence for a ubiquitous distribution of ARV infection in Egypt as well as represents a starting point for genetic characterization of the currently circulating ARV strains.

Induction of a robust immunity response against novel duck reovirus in ducklings using a subunit vaccine of sigma C protein

Novel duck reovirus (NDRV) disease emerged in China in 2011 and continues to cause high morbidity and about 5.0 to 50% mortality in ducklings. Currently there are no approved vaccines for the virus. This study aimed to assess the efficacy of a new vaccine created from the baculovirus and sigma C gene against NDRV. In this study, a recombinant baculovirus containing the sigma C gene was constructed, and the purified protein was used as a vaccine candidate in ducklings. The efficacy of sigma C vaccine was estimated according to humoral immune responses, cellular immune response and protection against NDRV challenge. The results showed that sigma C was highly expressed in Sf9 cells. Robust humoral and cellular immune responses were induced in all ducklings immunized with the recombinant sigma C protein. Moreover, 100% protection against lethal challenge with NDRV TH11 strain was observed. Summary, the recombinant sigma C protein could be utilized as a good candidate against NDRV infection.

Current limitations in control of viral arthritis and tenosynovitis caused by avian reoviruses in commercial poultry

Avian reoviruses are the causative agent of viral arthritis/tenosynovitis in chickens and turkeys. Clinical signs of disease include swelling of the hock joints accompanied by lesions in the gastrocnemius and digital flexor tendons causing lameness in addition to hydropericardium. The economic impact is significant as it results in poor weight gain, increased feed conversion ratios and condemnations at the processing plant. Vaccination with both live attenuated and inactivated oil emulsion vaccines have been used successfully for decades to control the disease. Current commercial vaccine strains belong to the same serotype and are antigenically and serologically distinct from circulating variant field viruses isolated from clinical cases of tenosynovitis. Since 2012, there has been a dramatic increase in the number of clinical cases of tenosynovitis in commercial poultry and commercial vaccines are unable to provide adequate levels of protection against disease. Producers have elected to use custom inactivated vaccines in the absence of any commercially available homologous vaccines. Identification and selection of field isolates for use in autogenous vaccines can be difficult especially when multiple reoviruses are co-circulating among flocks. In addition, field data suggests that in some cases the custom vaccines are providing adequate protection against disease but as new genetic variants emerge, new vaccines are needed.

Characterization of monoclonal antibodies against Muscovy duck reovirus sigmaB protein

BACKGROUND

The sigmaB protein of Muscovy duck reovirus (DRV), one of the major structural proteins, is able to induce neutralizing antibody in ducks, but the monoclonal antibody (MAb) against sigmaB protein has never been characterized.

RESULTS

Four hybridoma cell lines secreting anti-DRV sigmaB MAbs were obtained, designated 1E5, 2F7, 4E3 and 5D8. Immunoglobulin subclass tests differentiated them as IgG2b (1E5 and 4E3) and IgM (2F7 and 5D8). Dot blot and western blotting assays showed that MAbs reacted with His-sigmaB protein in a conformation-independent manner. Competitive binding assay indicated that the MAbs delineated two epitopes, A and B of sigmaB. Immunofluorescence assay indicated that the four MAbs could specifically bind to Vero cells infected with DRV and sigmaB was distributed diffusely in the cytoplasma of infected cells. MAbs had universal reactivity to all DRVs tested in an antigen-capture enzyme-linked immunosorbent assay.

CONCLUSION

Results of this research provide important information about the four monoclonal antibodies and therefore the MAbs may be useful candidate for the development of a MAb capture ELISA for rapid detection of DRVs. In addition, it showed that the sigmaB protein was located in the cytoplasma of infected cells by immunofluorescence assay with MAbs. Virus isolation and RT-PCR are reliable way for detection of DRV infection, but these procedures are laborious, time consuming, and requiring instruments. These obvious diagnosis problems highlight the ongoing demand of rapid, reproducible, and automatic methods for the sensitive detection of DRV.

Characterization of the σB-encoding genes of muscovy duck reovirus: σC–σB-ELISA for antibodies against duck reovirus in ducks

The sigmaB/sigmaC-encoding genes of muscovy duck reovirus (DRV) S12 strain were cloned, sequenced, and expressed in Escherichia coli. The sigmaC-encoding gene of DRV showed only 21-22% identity to that of avian reovirus (ARV) at both nucleotide and amino acid level. The sigmaB-encoding gene of DRV comprised 1163bp with one open reading frame (ORF). The ORF comprised 1104bp and encoded 367 amino acids with a predicted molecular mass of 40.44 kDa. A zinc-binding motif and a basic amino acid motif were found within the predicted amino acid sequence of sigmaB. The identities between the S12 and ARV were 59.3-64.0% and 60.9-62.5%, respectively, at the nucleotide and deduced amino acid levels. Phylogenetic analysis of the sigmaB-encoding gene sequence indicated that S12 separated as a distinct virus relative to other avian strains. The expressed sigmaB/sigmaC fusion proteins in E. coli could be detected, approximately 45 and 50kDa, respectively, by duck anti-reovirus polyclonal serum. In addition, an ELISA (sigmaB-sigmaC-ELISA) using the expressed sigmaB-sigmaC proteins as coating antigen for detection of antibodies to DRV in ducks was developed. In comparison with the virus neutralization test and agar gel immuno-diffusion test (AGID), the sigmaB-sigmaC-ELISA showed perfect specificity and sensitivity. The sigmaB-sigmaC-ELISA did not react with the antisera to other duck pathogens, implying that these two proteins were specific in recognition of DRV antibodies. Taken together, the results demonstrated that sigmaB-sigmaC-ELISA was a sensitive and accurate method for detecting antibodies to DRV.

Development and characterization of monoclonal antibodies against avian reovirus σC protein and their application in detection of avian reovirus isolates

Avian reovirus (ARV) is a non-enveloped virus with a segmented double-stranded RNA genome surrounded by a double icosahedral capsid shell. ARVs are associated with viral arthritis, immunosuppression, and enteric diseases in poultry. The sigma C protein was involved in induction of apoptosis and neutralization antibody. In the present study, sigma C-His protein was expressed in Sf9 insect cells and purified by immobilized metal affinity chromatography. Eight monoclonal antibodies (mAbs) against sigma C-His and three mAbs against His were screened from hybridoma cells produced by fusion of splenocytes from immunized mice with NS1 myeloma cells. Among the eight mAbs against sigma C protein, all belonged to the IgG isotype except three for IgM. It was discovered that all anti-His mAbs were mixtures of IgG and IgM isotypes. mAbs reacted with sigma C-His protein in a conformation-independent manner based on dot blot and western blotting assays. The competitive binding assay indicated that all mAbs recognized the same epitope on sigma C protein that was conserved in different isolates. Compared with the commercial anti-ARV S1133 polyclonal antibody, mAb (D15) had universal reactivity to all serotypes or genotypes of ARVs tested. This monoclonal antibody may therefore be useful for the development of an antigen-capture enzyme-linked immunosorbent assay for rapid detection of field isolates.

A monoclonal antibody-based competitive enzyme-linked immunosorbent assay for detecting antibody production against avian reovirus protein sigmaA

An assay protocol based on a monoclonal antibody-based competitive enzyme-linked immunosorbent assay (MAb-based c-ELISA) for detection of antibody against avian reovirus protein sigmaA in chicken is described. After the conditions for MAb-based c-ELISA had been optimized, sera collected from birds that received live and inactivated avian reovirus vaccines in different combinations were tested for antibody response against virus protein sigmaA. The results show a high level of antibody against sigmaA was in both vaccinated specific pathogenic free (SPF) and vaccinated commercially reared birds as long as one of the vaccines administered was in an inactivated form. The high level of antibody production is indicated by a high percentage inhibition (PI) values in the sera of the birds; but no antibody production was found in birds which received live vaccine only, as indicated by the low PI values. In serum samples from SPF birds receiving vaccines that include an inactivated form of the vaccine, there is a good correlation between the PI values and serum neutralizing antibody (SN) titers. Again, this correlation was not observed in birds that received only live vaccine. The PI values of commercially reared birds receiving inactivated vaccine were significantly different from those of the mock-treated birds, but this was not the case when the birds received only live vaccine. Taken together, the results suggest that MAb-based c-ELISA may provide an alternative choice for determining the immune status of a vaccinated chicken flock as long as one of the vaccines used was inactivated, and thus would allow a more precise way to predict the appropriate time for vaccination.

Antibody responses against avian reovirus nonstructural protein σNS in experimentally virus-infected chickens monitored by a monoclonal antibody capture enzyme-linked immunosorbent assay

Crude antigen preparations from avian reovirus (ARV)-infected chicken embryo fibroblasts (sigmaNS) or from bacterially expressed protein sigmaNS (esigmaNS) were captured by monoclonal antibody 1E1(MAb 1E1) against ARV nonstructural protein sigmaNS immobilized on the ELISA plates and were used as the MAb capture ELISA for antibody detection. Sixty one-week-old specific pathogenic free (SPF) chickens were divided into six groups and were vaccinated with live or inactivated ARV vaccine preparations in different combinations or inoculated with a virulent ARV strain. Sera collected from the birds were tested for their antibody responses to ARV nonstructural protein sigmaNS. Using the MAb capture ELISAs, the level of nonspecific binding reactions was tested on the serum samples obtained weekly from mock-infected SPF chickens from 1 to 25 weeks and compared to the results tested by the conventional ELISA. The results indicated that both MAb capture ELISAs had lower nonspecific bindings than those in the conventional ELISA, even in older birds. Antibody responses against ARV sigmaNS of the birds which received the inactivated vaccine twice (group I), inactivated vaccine followed by a live vaccine (group II), or a live vaccine followed by boosting with an inactivated vaccine (group III) were detected by MAb captured ELISA with sigmaNS crude antigens. The absorbance values increased rapidly at 1-2 weeks after boosting, approximated a peak at 5-6 weeks of age, and maintained this throughout the length of the experiment. The absorbance values of the MAb capture ELISA showed a good correlation to the SN titers ( r value > 0.85). On the other hand, serum samples from the birds which received the live vaccine twice (group IV) or were inoculated with a virulent ARV (group V) did not show antibody responses to sigmaNS, similar to those from the mock-infected birds (group VI), as the absorbance values maintained at a low level (below 0.5) throughout the length of the experiment. Similar results were obtained in the sera detected by MAb capture ELISA with crude esigmaNS antigens, except that the absorbance values in the sera from the birds in group III were gradually increased and later approximated a peak at 11 weeks of age and maintained this throughout the length of the experiments. The results suggest that MAb capture ELISAs can be readily used to detect antibody responses of the birds against ARV nonstructural protein sigmaNS which may reflect an immune status of a chicken flock, receiving ARV vaccine as long as including an inactivated vaccine.

Immune response to avian reovirus in chickens and protection against experimental infection

OBJECTIVES

To assess the efficacy of the vaccination procedure and the effect of the transfer of maternal antibodies to progeny chickens on reovirus pathogenicity.

DESIGN

To vaccinate chickens and challenge progeny chickens with high doses of homologous and heterologous viruses.

PROCEDURE

High doses of reovirus strains RAM-1, 1091 and 724 were used to induce tenosynovitis lesions. High doses were produced by concentration of viruses grown in cell culture. Then similar doses of viruses were used to challenge immunised chickens progeny.

RESULT

Vaccination of breeding hens with the RAM-1 strain of avian reovirus, which resulted in the passive transfer of neutralising antibody to progeny chickens, completely prevented the development of tenosynovitis in 80% of progeny chickens infected with the homologous virus. Even though multiple injections of hens resulted in broadening of the normal type-specificity of the neutralising antibody response against heterologous serotypes of avian reovirus, only marginal protection against strains of two heterologous serotypes of avian reovirus was obtained.

CONCLUSIONS

A model for assessing the efficacy of vaccination against avian reovirus strains on clinical sign such as tenosynovitis was developed that overcome the normal low virulence of Australian strains of avian reovirus. Breeding hens can be immunised with Australian strain of avian reovirus with passive transfer of antibody via the yolk to the progeny chickens. Although the neutralising antibody response to three injections of inactivated virus decreased the specificity of the neutralising antibody response against antigenically heterologous strains of avian reovirus, the protective immunity appeared to retain type-specificity.