Simultaneous detection of duck hepatitis A virus types 1 and 3, and of duck astrovirus type 1, by multiplex RT-PCR

Establishment of duplex SYBR Green I-based real-time PCR assay for simultaneous detection of duck hepatitis a virus-1 and duck astrovirus-3

Duck viral hepatitis (DVH) mainly affects ducklings under 1 month of age, causes liver necrosis, enlargement, and hemorrhage, and is highly lethal, seriously jeopardizing the duck industry. The prevalence of serotypes DHAV-1 and DAstV-3 is increasing, and co-infection is common. Moreover, the similar clinical characteristics of the DHAV-1 and DAstV-3 infections and high frequency of co-infection make diagnosis difficult. In this study, to establish a method for the rapid simultaneous detection of DHAV-1 and DAstV-3 , two pairs of specific primers were designed according to their conserved gene regions. A SYBR Green I-based real-time PCR assay was successfully established that can quickly and differentially detect the two viruses. Moreover, the assay is highly specific and does not show cross-reaction with other common viruses. The detection limit of the method is 7.34 × 10 1 copies/μL and 3.78 × 10 1 copies/μL for DHAV-1 and DAstV-3, respectively, indicating high sensitivity. A total of 34 clinical samples were tested using the established method; the positive rates for DHAV-1 and DAstV-3 was 14.71% and 8.82%, respectively, and that for co-infection was 2.94% (1/34), which was better than that obtained with conventional PCR. In summary, the SYBR Green I-based real-time PCR assay established in this study has high specificity, good sensitivity and accuracy, high feasibility, and is rapid. Thus, it can be a powerful tool for the co-infection detection of DHAV-1 and DAstV-3 and for future epidemiological studies.

Dual Circulation of Duck Hepatitis A Virus Genotypes 1 and 3 in Egypt

Duck hepatitis A virus (DHAV) causes acute hepatitis and mortality, resulting in high economic losses in the duck farm industry. The current study describes the outbreak of DHAV in vaccinated duck farms in North Egypt during 2019 and molecular characterization of the 3' untranslated region (UTR) and viral protein VP1 genes. The 30 samples were collected from 7- to 28-day-old commercial Pekin ducks that showed a history of nervous signs and sudden deaths and were on farms in 6 governorates. DHAV was typed by reverse transcription-polymerase chain reaction (RT-PCR) for 3' UTR and VP1 genes and revealed 20 positive farms, with the first detection of DHAV genotype 3 (DHAV-3) in 18 samples and the classic DHAV-1 in 2 samples. The phylogenetic analysis of VP1 and 3' UTR genes of the nine selected strains representative of six governorates revealed that seven strains were clustered with DHAV-3 Chinese and Korean-Vietnamese strains within different subgroups with 92.4%-93.7% amino acid identity; such strains were distinguishable from the vaccine strain of DHAV-1 used in Egypt with 74.4% amino acid identity. The other strains were closely related to the DHAV-1 Asian strain and the vaccine strain used in Egypt with 98.7%-99.6% amino acid identity for the VP1 gene with different clustering than that of recently isolated DHAV-1 Egyptian strains. The VP1 gene of DHAV-3 had 1 hypervariable region (HVR) with 10 amino acid mutations compared with DHAV3/DN2/Vietnam/2011, but DHAV-1 had 3 HVRs with 1 amino acid mutation in HVRII compared with the DHAV-1 vaccine strain. In conclusion, a new introduction of DHAV-3 with the classical DHAV-1 was recorded in Pekin duck farms in North Egypt that is genetically distant from the vaccinal strain.

The pathogenicity of duck hepatitis A virus types 1 and 3 on ducklings

Duck hepatitis A virus (DHAV) is one of the pathogens that cause fatal duck viral hepatitis (DVH) in ducklings, which is an acute and contagious disease with a high mortality rate. Despite a continuing official duck vaccination program, DHAV infection remains a major threat to the duck industry. Considerable changes were observed in the epidemiology of DHAV-1/-3 in China over time. Therefore, comparing the pathogenicity of different DHAV serotypes can provide a theoretical basis for the diagnosis and prevention of DVH. In this study, we systematically investigated the effects of infection with DHAV-1/-3 field strains on clinical signs, gross lesions, histopathological changes, viral RNA detection, enzymatic systems, and metabolite concentrations. The results demonstrated that the major macroscopic and microscopic lesions in ducks infected with DHAV-1/-3 in the liver, brain, spleen, pancreas, and kidneys exhibited no significant differences. After 24 h of infection, DHAV quickly appeared in blood and major organs. Significant changes in clinical chemical markers together with histopathological lesions and viral RNA detection indicated that the liver is the major target organ for both viruses, resulting in impaired of liver integrity and function. In addition, we found that both viruses were able to invade both central and peripheral immune organs. Also lipase plasma activity was substantially affected by DHAV-1/-3, indicating that the integrity and function of the pancreas was compromised. However, there was no significant difference in pathogenicity between DHAV-1 and -3. The results of this study provide new insights into the pathogenesis of DHAV-1/3, two viruses that cause serious depression, metabolic disorders, and immunosuppression.

A Novel Peptide Isolated from a Phage Display Peptide Library Modeling Antigenic Epitope of DHAV-1 and DHAV-3

Duck hepatitis A virus (DHAV), the major pathogen of duck virus hepatitis (DVH), causes severe diseases that threaten the duck industry worldwide. The VP1 protein, a major structural protein of DHAV, is able to induce neutralizing antibody in ducks. The purpose of this study was to identify the antigenic mimotope of DHAV by phage display technology. A monoclonal antibody (mAb) 4E6 against DHAV-1 and DHAV-3 was prepared, and a phage library prepared with the PhD-12 Phage Display Peptide Library Kit was screened with the mAb. A novel peptide, ¹GLTWKLPPSM¹⁰ was identified with high affinity to the mAb and could specifically block mAb 4E6 from binding DHAV-1 and DHAV-3. Animal tests confirmed that the immunization of ducklings with the mimotope could inhibit the virus proliferation and protect the ducklings from DVH. In summary, the neutralizing conformational mimotope ¹GLTWKLPPSM¹⁰ might be a promising vaccine candidate for the prevention of DHAV infection.

Identification of a Type-Specific Epitope in the ORF2 Protein of Duck Astrovirus Type 1

Simple Summary

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, using a monoclonal antibody (mAb) 3D2 against ORF2 protein of DAstV-1, a highly conserved linear B-cell epitope of ⁴⁵⁴ STTESA⁴⁵⁹ in DAstV-1 ORF2 was identified. The mAb 3D2 showed no neutralizing activity to DAstV-1 and had no cross-reactivity with other DAstV serotypes.

Abstract

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, a monoclonal antibody (mAb) 3D2 against open reading frame 2 (ORF2) protein of DAstV-1 was used to identify the possible epitope in the four serotypes of DAstV. The mAb 3D2 showed no neutralization activity to DAstV-1, and reacted with the conserved linear B-cell epitopes of ⁴⁵⁴STTESA⁴⁵⁹ in DAstV-1 ORF2 protein. Sequence analysis, dot blot assay, and cross-reactivity test indicated that the epitope peptide was highly conserved in DAstV-1 sequence and mAb 3D2 had no cross-reactivity with other DAstV serotypes. To the best of our knowledge, this is the first report about identification of the specific conserved linear B-cell epitope of DAstV-1, which will facilitate the serologic diagnosis of DAstV-1 infection.

Oral vaccine of recombinant Lactococcus lactis expressing the VP1 protein of duck hepatitis A virus type 3 induces mucosal and systemic immune responses

Duck hepatitis A virus (DHAV) is the major pathogen of duck viral hepatitis, which has caused great economic losses to duck breeding industry. As an effective delivery tool for protein antigens, Lactococcus lactis (L. lactis) has been successfully used to stimulate mucosal and systemic immune response. In this study, a recombinant L. lactis named NZ3900-VP1 was constructed, which could express VP1 protein of DHAV type 3 (DHAV-3) by using a nisin-controlled expression (NICE) system. The animal experiment in both mice and ducklings were performed to detect the immune response and protection effect of oral vaccination by the recombinant L. lactis. The results showed that oral vaccination with L. lactis NZ3900-VP1 significantly induced specific anti-VP1 IgG antibodies and mucosal secretory immunoglobulin A (sIgA) of DHAV-3 in mice and ducklings, and cytokines including interleukin-2 (IL-2), interferon gamma (IFN-γ), interleukin-10 (IL-10) and interleukin-4 (IL-4). Notably, the ducklings vaccinated with L. lactis NZ3900-VP1 were effectively protected when facing natural infestation of DHAV-3, which indicated that the recombinant L. lactis could serve as an effective vaccine to prevent DHAV-3 infection in ducklings.

Astrovirus Diagnostics

Various methods exist to detect an astrovirus infection. Current methods include electron microscopy (EM), cell culture, immunoassays, polymerase chain reaction (PCR) and various other molecular approaches that can be applied in the context of diagnostic or in surveillance studies. With the advent of metagenomics, novel human astrovirus (HAstV) strains have been found in immunocompromised individuals in association with central nervous system (CNS) infections. This work reviews the past and current methods for astrovirus detection and their uses in both research laboratories and for medical diagnostic purposes.

Live Attenuated Vaccine Based on Duck Enteritis Virus against Duck Hepatitis A Virus Types 1 and 3

As causative agents of duck viral hepatitis, duck hepatitis A virus type 1 (DHAV-1) and type 3 (DHAV-3) causes significant economic losses in the duck industry. However, a licensed commercial vaccine that simultaneously controls both pathogens is currently unavailable. Here, we generated duck enteritis virus recombinants (rC-KCE-2VP1) containing both VP1 from DHAV-1 (VP1/DHAV-1) and VP1 from DHAV-3 (VP1/DHAV-3) between UL27 and UL26. A self-cleaving 2A-element of FMDV was inserted between the two different types of VP1, allowing production of both proteins from a single open reading frame. Immunofluorescence and Western blot analysis results demonstrated that both VP1 proteins were robustly expressed in rC-KCE-2VP1-infected chicken embryo fibroblasts. Ducks that received a single dose of rC-KCE-2VP1 showed potent humoral and cellular immune responses and were completely protected against challenges of both pathogenic DHAV-1 and DHAV-3 strains. The protection was rapid, achieved as early as 3 days after vaccination. Moreover, viral replication was fully blocked in vaccinated ducks as early as 1 week post-vaccination. These results demonstrated, for the first time, that recombinant rC-KCE-2VP1 is potential fast-acting vaccine against DHAV-1 and DHAV-3.