DNA vaccination with a gene encoding VP60 elicited protective immunity against rabbit hemorrhagic disease virus

Co-circulation of GI.1 and GI.2 genotypes of rabbit hemorrhagic disease virus in Egypt

Recently, Egypt has experienced an increased incidence of rabbit hemorrhagic disease virus (RHDV) infection even among vaccinated rabbits. The present study estimates the emergence of RHDV in vaccinated (n = 10) and unvaccinated (n = 8) domestic rabbitries in Beheira and Kafr El-Sheikh provinces, Egypt, during the period 2018-2020. A total of 8 out of 18 (44.4%) liver extracts were able to agglutinate human type O RBCs with HA titers ranged from 8 to 12 log2, and then subsequently confirmed for the presence of RHDV RNA using a reverse transcriptase-polymerase chain reaction (RT-PCR). The VP60 gene sequences of three selected isolates, designated Beh-1, Beh-9 and kaf-14, were submitted to the GenBank database and the accession numbers MZ782083 to MZ782085 were assigned, respectively. Phylogenetic analysis revealed that the Kaf-14 isolate was placed into the GI.1 genotype, while the Beh-1 and Beh-9 isolates were grouped into the GI.2 genotype. Overall, the three isolates shared 78.6-98.7%.nucleotide identity with previously published Egyptian sequences. In comparison with the GI.1a Giza2006 vaccine strain, the three isolates exhibited divergence ranging from 4.5 to 17.4% at the amino acid level. Approximately 55.5-87.5% of the amino acid substitutions were located in the P2 subdomain of the VP60 capsid protein which contains the main determinants of antigenicity and cellular recognition. In conclusion, our results provide crucial evidence for the co-circulation of RHDV GI.1 and GI.2 genotypes in Egypt and highlight the antigenic diversity among vaccine and field strains. Therefore, new effective vaccines are urgently required to counter the spread of GI.1 and GI.2 genotypes in Egypt.

Thermostable Vaccines in Veterinary Medicine: State of the Art and Opportunities to Be Seized

The COVID-19 pandemic has highlighted the weakness of the vaccine supply chain, and the lack of thermostable formulations is one of its major limitations. This study presents evidence from peer-reviewed literature on the development of thermostable vaccines for veterinary use. A systematic review and meta-analysis were performed to evaluate the immunogenicity and/or the efficacy/effectiveness of thermostable vaccines against infectious diseases. The selected studies (n = 78) assessed the vaccine’s heat stability under different temperature conditions and over different periods. Only one study assessed the exposure of the vaccine to freezing temperatures. Two field studies provided robust evidence on the immunogenicity of commercial vaccines stored at temperatures far in excess of the manufacturer’s recommended cold-chain conditions. The drying process was the most-used method to improve the vaccine’s thermostability, along with the use of different stabilizers. The pooled vaccine efficacy was estimated to be high (VE = 69%), highlighting the importance of vaccination in reducing the economic losses due to the disease impact. These findings provide evidence on the needs and benefits of developing a portfolio of heat- and freeze-stable veterinary vaccines to unleash the true potential of immunization as an essential component of improved animal health and welfare, reduce the burden of certain zoonotic events and thus contribute to economic resilience worldwide.

A Review on the Methods Used for the Detection and Diagnosis of Rabbit Hemorrhagic Disease Virus (RHDV)

Since the early 1980s, the European rabbit (Oryctolagus cuniculus) has been threatened by the rabbit hemorrhagic disease (RHD). The disease is caused by a lagovirus of the family Caliciviridae, the rabbit hemorrhagic disease virus (RHDV). The need for detection, identification and further characterization of RHDV led to the development of several diagnostic tests. Owing to the lack of an appropriate cell culture system for in vitro propagation of the virus, much of the methods involved in these tests contributed to our current knowledge on RHD and RHDV and to the development of vaccines to contain the disease. Here, we provide a comprehensive review of the RHDV diagnostic tests used since the first RHD outbreak and that include molecular, histological and serological techniques, ranging from simpler tests initially used, such as the hemagglutination test, to the more recent and sophisticated high-throughput sequencing, along with an overview of their potential and their limitations.

Restricted Host Specificity of Rabbit Hemorrhagic Disease Virus Is Supported by Challenge Experiments in Immune-compromised Mice ( Mus musculus)

Rabbit hemorrhagic disease virus (RHDV) is a highly contagious calicivirus that causes peracute hemorrhagic fever and frequently kills rabbits before an effective adaptive immune response can be developed. In Australia and New Zealand, RHDV is employed to manage wild European rabbit ( Oryctolagus cuniculus) populations. Although there is no evidence that RHDV replicates in animals other than lagomorphs, the detection of RHDV-specific antibodies and RHDV RNA in mice and other species has raised concerns about the host specificity of the virus. To investigate the replication potential of RHDV in mice ( Mus musculus), standard laboratory mice and knockout animals that lack a functional interferon type I receptor were challenged with high doses of RHDV. None of the animals developed clinical signs of illness, and temporal quantification of the viral RNA by real-time PCR did not reveal signs of virus amplification. These data suggest that RHDV cannot replicate in mice-not even in animals with a severely compromised innate immune system.

Efficacy of a commercial vaccine against different strains of rabbit haemorrhagic disease virus

BACKGROUND

This study investigated the ability of a commercial rabbit haemorrhagic disease virus (RHDV) vaccine (Cylap®) to protect rabbits from disease caused by two different strains of the virus (v351 and K5) that are used or proposed to be used for wild rabbit control in Australia. These strains of the RHDV1 genotype belong to the 'classical RHDV' and 'antigenic variant RHDVa' subtypes, respectively.

METHODS

Vaccinated rabbits were exposed to very high doses of the virus either by direct oral dosing or by exposure to infected rabbit livers.

RESULTS & CONCLUSION

All vaccinated rabbits were protected against rabbit haemorrhagic disease, indicating that the Cylap® vaccine is effective against both strains of the virus under experimental conditions.

Recombinant canine adenovirus type 2 expressing rabbit hemorrhagic disease virus VP60 protein provided protection against RHD in rabbits

Rabbit hemorrhagic disease virus (RHDV) is responsible for rabbit hemorrhagic disease (RHD), which is an acute, lethal and highly contagious disease in both wild and domestic rabbits. Although current vaccines are highly effective for controlling RHD, they are derived from infected rabbit livers and their use is thus associated with safety and animal-welfare concerns. In this study, we generated a recombinant lentogenic canine adenovirus type 2 (CAV2) vector expressing the RHDV vp60 gene, named rCAV2-VP60. rCAV2-VP60 expressed VP60 protein in Madin-Darby canine kidney cells as demonstrated by western blot and immunofluorescence assay. Polymerase chain reaction confirmed that the vp60 gene was successfully inserted into rCAV2-VP60 and was still detectable after 20 passages, indicating its stable genetic character. We evaluated the feasibility of rCAV2-VP60 as a live-virus-vectored RHD vaccine in rabbits. rCAV2-VP60 significantly induced specific antibodies to RHDV and provided effective protection against RHDV lethal challenge. These results suggest that rCAV2 expressing RHDV VP60 could be a safe and efficient candidate vaccine against RHDV in rabbits.

Self-assembly of virus-like particles of rabbit hemorrhagic disease virus capsid protein expressed in Escherichia coli and their immunogenicity in rabbits

In this study, virus-like particles (VLPs) derived from rabbit hemorrhagic disease virus (RHDV) were evaluated for the development of a vaccine against RHDV infection. The VP60 gene was cloned and inserted into a pSMK expression vector containing a small ubiquitin-like modifier (SUMO) tag that can promote the soluble expression of heterologous proteins in Escherichia coli cells. After expression and purification of His-SUMO-VP60 and cleavage of the SUMO tag, we found that the RHDV VP60 protein had self-assembled into VLPs with a similar shape and smaller size compared with authentic RHDV capsid. Next, the antigenicity and immunogenicity of the VLPs were examined. The results showed that RHDV-specific responses were clearly induced in rabbits and that all rabbits in the VLP group survived while those in the negative control group died within 72 h post-infection. These results suggest that VLP-based RHDV could be a promising RHDV vaccine candidate.