Comparative analysis of rabbit hemorrhagic disease virus strains originating from outbreaks in the Russian Federation

[Antigenic and immunogenic activity of virus-like particles based on rabbit hemorrhagic disease virus (Caliciviridae: Lagovirus) genotypes GI1 and GI2 recombinant major capsid proteins]

INTRODUCTION

Rabbit hemorrhagic disease is an acute highly contagious infection associated with two genotypes of pathogenic Lagovirus. Antibodies to major capsid protein (Vp60) are protective. The aim of the work ‒ is an evaluation of antigenic and immunogenic activity of virus-like particles (VLPs) based on recombinant major capsid proteins of both genotypes of rabbit hemorrhagic disease virus (RHDV) (recVP60-GI1 and recVP60-GI2).

MATERIALS AND METHODS

Baculovirus-expressed VLPs were evaluated using electron microscopy and administered to clinically healthy 1.53 month old rabbits in a dose of 50 g. Rabbits were challenged with 103 LD50 of virulent strains Voronezhsky-87 and Tula 21 days post immunization. Serum samples were tested for the presence of RHDV-specific antibodies.

RESULTS

VLPs with hemagglutination activity forming VLP 3040 nm in size were obtained in Hi-5 cell culture. Specific antibody titers in rabbits measured by ELISA were 1 : 200 to 1 : 800 on 21th day post immunization with VLPs. Immunogenic activity of recVP60-GI1 VLPs was 90 and 40%, while it was 30 and 100% for recVP60-GI2 VLPs after the challenge with RHDV genotypes 1 and 2 respectively. The immunogenicity of two VLPs in mixture reached 100%.

DISCUSSION

VLPs possess hemagglutinating, antigenic and immunogenic activity, suggesting their use as components in substances designed for RHDV specific prophylaxis in rabbits. Results of the control challenge experiment demonstrated the need to include the antigens from both RHDV genotypes in the vaccine.

CONCLUSION

Recombinant proteins recVP60-GI1 and recVP60-GI2 form VLPs that possess hemagglutinating an antigenic activity, and provide 90100% level of protection for animals challenged with RHDV GI1 and GI2 virulent strains.

Immune response in the recombinant strain of Lagovirus europaeus GI.1a

Lagovirus europaeus/GI.1 is the virus that causes severe and dangerous rabbit haemorrhagic disease (RHD) in rabbits. Recombination formation in RHD viruses is common. Recombination is thought to play a key role in the evolution of lagoviruses and therefore most likely influences the pathogenicity of L. europaeus/GI strains. Immunological events also play a key role in the control of RHD, and an in-depth knowledge of these phenomena provides insights into the characteristics of the infection, which can help implement appropriate infection control measures. To obtain a more complete picture of RHD caused by different GI.1 strains, it is necessary to correlate the genetic diversity within L. europaeus/GI.1 strains and the immune picture in response to infection. We performed a phylogenetic analysis of the L. europaeus/GI strains and compared the recombinant L. europaeus/GI.1 strain with the GI.1a strain on the basis of a thorough statistical analysis of immunological traits performed previously. Our phylogenetic analysis based on the sequence of the gene encoding the VP60 capsid protein of 34 strains of Lagovirus europaeus showed that the Hartmannsdorf strain forms a separate clade from the other GI.1a strains and is separate from the GI.1b-d strains. Next, we showed significant differences in the levels of individual parameters for non-specific cellular and humoral immunity in infection with the GI.1a strain and the Hartmannsdorf recombinant strain. Against the background of this study, our results indicate that the characteristics of each recombinant should be considered individually.

Detection and characterisation of rabbit haemorrhagic disease virus strains circulating in Egypt

Rabbit haemorrhagic disease (RHD) is a highly virulent viral disease of Oryctolagus cuniculus which threatens the rabbit population in Egypt and worldwide. The etiological agent is the rabbit haemorrhagic disease virus (RHDV), a member of the family Caliciviridae. The aim of this study was to identify the possible evolutionary changes of the currently circulating RHDV in Egypt. Twenty suspected cases were collected from outbreaks that occurred in non-vaccinated rabbit flocks during 2015 and 2016. Liver homogenate samples were investigated for detection and identification of circulating RHDV using haemagglutination (HA) and reverse transcriptase polymerase chain reaction. Further characterisation of selected five viral strains was performed by nucleotide sequencing of VP60 gene. All twenty tested samples were haemagglutinin positive and VP60 gene was amplified. Based on nucleotide sequence analysis, four isolates were identified as classical RHDV strains, while one isolate was assigned as RHDVa variant strain but with the same HA pattern. The new RHDVb variant was not identified.

Detection and Circulation of a Novel Rabbit Hemorrhagic Disease Virus in Australia

The highly virulent rabbit hemorrhagic disease virus (RHDV) has been widely used in Australia and New Zealand since the mid-1990s to control wild rabbits, an invasive vertebrate pest in these countries. In January 2014, an exotic RHDV was detected in Australia, and 8 additional outbreaks were reported in both domestic and wild rabbits in the 15 months following its detection. Full-length genomic analysis revealed that this virus is a recombinant containing an RHDVa capsid gene and nonstructural genes most closely related to nonpathogenic rabbit caliciviruses. Nationwide monitoring efforts need to be expanded to assess if the increasing number of different RHDV variants circulating in the Australian environment will affect biological control of rabbits. At the same time, updated vaccines and vaccination protocols are urgently needed to protect pet and farmed rabbits from these novel rabbit caliciviruses.