Development of a live attenuated duck hepatitis A virus type 3 vaccine (strain SD70)

Development of the first officially licensed live attenuated duck hepatitis A virus type 3 vaccine strain HB80 in China and its protective efficacy against DHAV-3 infection in ducks

Duck hepatitis A virus type 3 (DHAV-3) is an infectious virus that is highly fatal to ducklings and causes significant economic losses in the duck industry worldwide. Biosecurity and vaccination are required to control the pathogen. In the present study, we attenuated a lowly pathogenic DHAV-3 clinical isolate, named as HB, by serial passaging in duck embryos, and followed by several adaptive proliferations in specific-pathogen-free (SPF) chicken embryos. The virulence of DHAV-3 at different passages was assessed by infecting 3-day-old ducklings. We found that the HB strain lost pathogenicity to ducklings from the 55th passage onwards. The 80th passage strain (HB80), which achieved good growth capacity in duck embryos with a viral titer of 108.17 50% egg lethal dose per milliliter (ELD50/mL), was selected as a live attenuated vaccine candidate. The HB80 strain did not induce clinical symptoms or pathological lesions in 3-day-old ducklings and showed no virulence reversion after 5 rounds of in vivo back-passage. The minimum effective dose of HB80 was determined to be 104.5 ELD50 by hypodermic inoculation of the neck. Importantly, a single dose of HB80 elicited good immune responses and provided complete protection against challenge with the lethal DHAV-3 strain. Compared with the genomic sequence of the parental HB strain, HB80 had 7 amino acid substitutions, two of them are in the hypervariable region of the VP1 and polymerase-encoding 3D regions, which may play a role in virulence attenuation. Our data suggest that the attenuated HB80 strain is a promising vaccine candidate for the prevention of DHAV-3 infections in China. HB80 has been registered as a New Veterinary Drug Registration Certificate by the Chinese Ministry of Agriculture and Rural Affairs (MARA), and is the first live attenuated DHAV-3 vaccine strain to be officially licensed in China.

Overview of the recent advances in porcine epidemic diarrhea vaccines

Vaccination is the most effective means of preventing and controlling porcine epidemic diarrhea (PED). Conventional vaccines developed from porcine epidemic diarrhea virus (PEDV) GI-a subtypes (CV777 and SM98) have played a vital role in preventing classical PED. However, with the emergence of PEDV mutants in 2010, conventional PEDV GI-a subtype-targeting vaccines no longer provide adequate protection against PEDV GII mutants, thereby making novel-type PED vaccine development an urgent concern to be addressed. Novel vaccines, including nucleic acid vaccines, genetically engineered subunit vaccines, and live vector vaccines, are associated with several advantages, such as high safety and stability, clear targeting, high yield, low cost, and convenient usage. These vaccines can be combined with corresponding ELISA kits to differentiate infected from vaccinated animals, which is beneficial for disease confirmation. This review provides a detailed overview of the recent advancements in PED vaccines, emphasizing on the research and application evaluation of novel PED vaccines. It also considers the future directions and challenges in advancing these vaccines to widespread use in clinics.

Identification of the genetic characteristics of copy number variations in experimental specific pathogen-free ducks using whole-genome resequencing

BACKGROUND

Specific pathogen-free ducks are a valuable laboratory resource for waterfowl disease research and poultry vaccine development. High throughput sequencing allows the systematic identification of structural variants in genomes. Copy number variation (CNV) can explain the variation of important duck genetic traits. Herein, the genome-wide CNVs of the three experimental duck species in China (Jinding ducks (JD), Shaoxing ducks (SX), and Fujian Shanma ducks (SM)) were characterized using resequencing to determine their genetic characteristics and selection signatures.

RESULTS

We obtained 4,810 CNV regions (CNVRs) by merging 73,012 CNVs, covering 4.2% of the duck genome. Functional analysis revealed that the shared CNVR-harbored genes were significantly enriched for 31 gene ontology terms and 16 Kyoto Encyclopedia of Genes and Genomes pathways (e.g., olfactory transduction and immune system). Based on the genome-wide fixation index for each CNVR, growth (SPAG17 and PTH1R), disease resistance (CATHL3 and DMBT1), and thermoregulation (TRPC4 and SLIT3) candidate genes were identified in strongly selected signatures specific to JD, SM, and SX, respectively.

CONCLUSIONS

In conclusion, we investigated the genome-wide distribution of experimental duck CNVs, providing a reference to establish the genetic basis of different phenotypic traits, thus contributing to the management of experimental animal genetic resources.

A meta-analysis for vaccine protection rate of duck hepatitis a virus in mainland China in 2009-2021

BACKGROUND

Duck hepatitis A virus (DHAV) is a single-stranded, positive-strand small RNA virus that causes a very high mortality rate in ducklings. The DHAV-3 subtype incidence rate has recently increased in China, causing great economic losses to the waterfowl breeding industry. We analyzed the protection rate of DHAV vaccines used in mainland China from 2009 to 2021 and evaluated the effectiveness of vaccine prevention and control to reduce the economic losses caused by DHAV to the waterfowl breeding industry. We screened five electronic research databases and obtained 14 studies and patents on the protection efficiency of DHAV-1 and DHAV-3 vaccines.

RESULTS

Meta-analysis demonstrated that immunized ducklings produced higher antibody levels and had a significantly higher survival rate than non-immunized ducklings [relative risk (RR) = 12, 95% confidence interval (CI) 6-26, P < 0.01]. The age of the ducks and vaccine valence did not affect protection efficiency. Data source analysis of the vaccine protection rate demonstrated that the vaccines conferred immune protection for ducklings in both small-scale experiments and large-scale clinical conditions. The analysis results revealed that although the vaccines conferred protection, the immune protective effect differed between small-scale experimental conditions and large-scale clinical conditions. This might have been due to non-standard vaccination and environmental factors.

CONCLUSIONS

Domestic DHAV vaccines can protect ducklings effectively. The subjects immunized (breeding ducks or ducklings) and vaccine valence had no effect on the protective effect. Both small-scale experiments and large-scale clinical conditions conferred immune protection on ducklings, but vaccine immunization under small-scale experimental conditions had slightly better protective effects than large-scale clinical immunization.

Whole-genome resequencing to unveil genetic characteristics and selection signatures of specific pathogen-free ducks

Specific pathogen-free ducks are important high-grade laboratory animals, with a key role in research related to poultry biosecurity, production, and breeding. However, the genetic characteristics of experimental duck varieties remain poorly explored. Herein we performed whole-genome resequencing to construct a single nucleotide polymorphism genetic map of the genomes of 3 experimental duck varieties [Jinding ducks (JD), Shaoxing ducks (SX), and Fujian Shanma ducks (SM)] to determine their genetic characteristics and identify selection signatures. Subsequent analyses of population structure and genetic diversity revealed that each duck variety formed a monophyletic group, with SM showing richer genetic diversity than JD and SX. Further, on exploring shared selection signatures, we found 2 overlapping genomic regions on chromosome Z of all experimental ducks, which comprised immune response-related genes (IL7R and IL6ST). Moreover, growth and skeletal development (IGF1R and GDF5), meat quality (FoxO1), and stress resistance (HSP90B1 and Gpx8-b) candidate gene loci were identified in strongly selected signatures specific to JD, SM, and SX, respectively. Our results identified the population genetic basis of experimental ducks at the whole-genome level, providing a framework for future molecular investigations of genetic variations and phenotypic changes. We believe that such studies will eventually contribute to the management of experimental animal resources.

Current status and future direction of duck hepatitis A virus vaccines

Duck viral hepatitis (DVH), mainly caused by duck hepatitis A virus (DHAV), is a highly fatal and rapidly spreading infectious disease of young ducklings that seriously jeopardizes the duck industry worldwide. DHAV type 1 (DHAV-1) is the main genotype responsible for disease outbreaks since 1945, and the disease situation is complicated by the emergence and dissemination of a novel genotype (DHAV-3) in some countries in Asia and Africa. Live attenuated DHAV vaccines are widely used to induce a considerable degree of protection in ducklings. Breeder ducks are immunized with inactivated or/and live DHAV vaccines to achieve satisfactory levels of passive immunity in progeny. In addition, novel characteristics of virus transmission, pathogenicity and pathogenesis of DHAV were recently characterized, necessitating the development of new vaccines and effective vaccination programmes against DVH. Therefore, a systematic dissection of the profiles, strengths and shortcomings of the available DHAV vaccines is essential. Moreover, to further increase the efficiency of vaccine production and administration, the development of next-generation DHAV vaccines using cutting-edge technologies is also required. In this review, based on a comprehensive summary of the research advances in the epidemiology, pathogenicity, and genomic features of DHAV, we focus on reviewing and analysing the features of the commercial and experimental DHAV vaccines. We also propose perspectives for disease control based on the specific disease situations in different countries. This review provides essential information for vaccine development and disease control of DVH.

Optimization of Heat-Resistance Technology for a Duck Hepatitis Lyophilized Live Vaccine

In this study, to improve the quality of a live attenuated vaccine for duck viral hepatitis (DHV), the lyophilization of a heat-resistant duck hepatitis virus vaccine was optimized. The optimized heat protectors were made of 10% sucrose, 1.2% pullulan, 0.5% PVP, and 1% arginine, etc., with a titer freeze-drying loss of ≤0.50 Lg. The vaccine product’s valence measurements demonstrated the following: the vaccine could be stored at 2–8 °C for 18 months with a virus titer loss ≤0.91 Lg; at 37 °C for 10 days with a virus valence loss ≤0.89 Lg; and at 45 °C for 3 days with a virus titer loss ≤0.90 Lg. Regarding safety, no deaths occurred in two-day-old ducklings immunized with a 10 times dose vaccine; their energy, diet, and weight gain were all normal, demonstrating that the DHV heat-resistant vaccines were safe for ducklings and did not cause any immune side effects. Duck viral hepatitis freeze-dried vaccine began to produce antibodies at 7 d after immunization, reached above 5.0 on 14 d, and reached above 7.0 on 21 d, showing a continuous upward trend. This indicates that duck viral hepatitis vaccine has a good immunogen level. The optimization of the freeze-drying process saves costs and also improves the quality of the freeze-drying products, which provides important theoretical and technical support for the further study of vaccine products.

NOD1 Is Associated With the Susceptibility of Pekin Duck Flock to Duck Hepatitis A Virus Genotype 3

Duck viral hepatitis (DVH) is an acute, highly lethal infectious disease of ducklings that causes huge losses in the duck industry. Duck hepatitis A virus genotype 3 (DHAV-3) has been one of the most prevalent DVH pathogen in the Asian duck industry in recent years. Here, we investigated the genetic basis of the resistance and susceptibility of ducks to DVH by comparing the genomes and transcriptomes of a resistant Pekin duck flock (Z8) and a susceptible Pekin duck flock (SZ7). Our comparative genomic and transcriptomic analyses suggested that NOD1 showed a strong signal of association with DVH susceptibility in ducks. Then, we found that NOD1 showed a significant expression difference between the livers of susceptible and resistant individuals after infection with DHAV-3, with higher expression in the SZ7 flock. Furthermore, suppression and overexpression experiments showed that the number of DHAV-3 genomic copies in primary duck hepatocytes was influenced by the expression level of NOD1. In addition, in situ RNAscope analysis showed that the localization of NOD1 and DHAV-3 in liver cells was consistent. Altogether, our data suggested that NOD1 was likely associated with DHAV-3 susceptibility in ducks, which provides a target for future investigations of the pathogenesis of DVH.