Etiology of viral induced acute liver failure and defensins as potential therapeutic agents in ALF treatment

Acute liver failure (ALF) is a rare and severe disease, which, despite continuous advances in medicine, is still characterized by high mortality (65-85%). Very often, a liver transplant is the only effective treatment for ALF. Despite the implementation of prophylactic vaccinations in the world, the viral background of ALF is still a problem and leads to many deaths. Depending on the cause of ALF, it is sometimes possible to reverse this condition with appropriate therapies, which is why the search for effective antiviral agents seems to be a very desirable direction of research. Defensins, which are our natural antimicrobial peptides, have a very high potential to be used as therapeutic agents for infectious liver diseases. Previous studies on the expression of human defensins have shown that increased expression of human α and β-defensins in HCV and HBV infections is associated with a better response to treatment. Unfortunately, conducting clinical trials for ALF is very difficult due to the severity of the disease and the low incidence, therefore animal models are important for the development of new therapeutic strategies. One of the best animal models that has real reference to research on acute liver failure (ALF) is rabbit hemorrhagic disease in rabbits caused by the Lagovirus europaeus virus. So far, there have been no studies on the potential of defensins in rabbits infected with Lagovirus europaeus virus.

Detection of Rabbit Hemorrhagic Disease Virus 2 in the Pygmy Rabbit (Brachylagus idahoensis) in Nevada, USA

Rabbit hemorrhagic disease virus 2 (RHDV2 or Lagovirus GI.2) began circulating in wild lagomorph populations in the US in March 2020. To date, RHDV2 has been confirmed in several species of cottontail rabbits (Sylvilagus spp.) and hares (Lepus spp.) throughout the US. In February 2022, RHDV2 was detected in a pygmy rabbit (Brachylagus idahoensis). Pygmy rabbits are sagebrush obligates that only occur in the US Intermountain West and are a species of special concern due to the continual degradation and fragmentation of sagebrush-steppe landscapes. The spread of RHDV2 into occupied pygmy rabbit sites may pose a significant threat to their populations because of already declining numbers associated with habitat loss and high mortality rates.

Case series: Four fatal rabbit hemorrhagic disease virus infections in urban pet rabbits

Four pet rabbits (Oryctolagus cuniculus cuniculus) diagnosed with a fatal infection by rabbit hemorrhagic disease virus (RHDV GI.2) were identified in the same week and further investigated. All animals lived in an urban environment (Lisbon, Portugal), were between 8 months and 2 years old and none had been vaccinated against RHDV2 (GI.2). Three animals arrived at the clinic and died shortly afterward and it was only possible to collect material for RT-qPCR (RHDV) test. These rabbits tested positive for RHDV2, with high viral loads. In the fourth case, additional clinical and post-mortem gross and histological evaluations were performed. This 8 month old intact female indoor pet rabbit was presented with apathy, tachypnea and tachycardia. Radiographic projections revealed no clinical revealed no clinical abnormalities. Serum biochemistry revealed a significant increase in AST and ALT with a small hypoglycemia. Abdominal ultrasound revealed an acute hepatitis. Despite hospitalization support, after 30 h of admission, the rabbit lost consciousness and developed anorexia and pyrexia in the last minutes before death. Post-mortem analysis and molecular testing by RT-qPCR, confirmed the diagnosis of RHDV2 (GI.2) infection also with high viral load. In conclusion, this paper reports a case series that demonstrates the severe infectious ability and the high mortality associated with RHDV even in rabbits from urban environments. Furthermore, it highlights the importance of always considering rabbit hemorrhagic disease (RHD) as a differential diagnosis in pet rabbits with non-specific clinical signs, and should warn veterinarians that pet rabbits living indoors can also be infected with a fatal outcome.

Occurrence of Lagovirus europaeus (Rabbit Hemorrhagic Disease Virus) in Domestic Rabbits in Southwestern Poland in 2019: Case Report

Lagovirus europaeus (rabbit hemorrhagic disease virus [RHDV]) is a small, nonenveloped, single-stranded RNA virus that causes a severe, highly infectious, and fatal disease in rabbits (Oryctolagus cuniculus) called rabbit hemorrhagic disease (RHD). Since its discovery in the 1980s, it has posed a very serious threat to the global rabbit industry and the rabbit population in the wild. According to data from 2005 to 2018, the occurrence of RHD has been reported or suspected in 50 countries, with more than one-half of the reports being recorded in European countries. The main aim of the study was to detect Lagovirus europaeus (RHDV) strains found in domestic rabbits that died suddenly in the city of Wrocław in southwest Poland. All animals (n = 14) tested in this study died naturally and showed macroscopic features at necropsy that indicated the possibility of death from RHD. As a result of the research, the presence of L. europaeus virus was confirmed in 8 samples of all 14 samples collected. All strains of Lagovirus europaeus isolated in the present study showed 100% nucleotide identity to L. europaeus GI.1 strain FRG and a strain isolated in New Zealand, as well as the L. europaeus GI.1a Erfurt strain. This suggests that it is likely that L. europaeus GI.2 strains have so far not displaced L. europaeus GI.1 strains from the environment in Poland. IMPORTANCE Lagovirus europaeus (RHDV) causes a severe, highly infectious, and fatal disease in rabbits called RHD. The disease is a very serious threat to the global rabbit industry and the rabbit population in the wild. The aim of the study was to detect Lagovirus europaeus (RHDV) strains in domestic rabbits that died suddenly in Poland. The presence of RHDV was confirmed in 8 samples of all 14 samples collected. This is one of the very few reports on the existence of this virus in pet rabbits in Poland.

Potent Protease Inhibitors of Highly Pathogenic Lagoviruses: Rabbit Hemorrhagic Disease Virus and European Brown Hare Syndrome Virus

Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are highly contagious diseases caused by lagoviruses in the Caliciviridae family. These infectious diseases are associated with high mortality and a serious threat to domesticated and wild rabbits and hares, including endangered species such as riparian brush rabbits (Sylvilagus bachmani riparius). In the United States (U.S.), only isolated cases of RHD had been reported until Spring 2020. However, RHD caused by GI.2/rabbit hemorrhagic disease virus (RHDV)2/b was unexpectedly reported in April 2020 in New Mexico and has subsequently spread to several U.S. states, infecting wild rabbits and hares and making it highly likely that RHD will become endemic in the U.S. Vaccines are available for RHD; however, there is no specific treatment for this disease. Lagoviruses encode a 3C-like protease (3CLpro), which is essential for virus replication and a promising target for antiviral drug development. We have previously generated focused small-molecule libraries of 3CLpro inhibitors and demonstrated the in vitro potency and in vivo efficacy of some protease inhibitors against viruses encoding 3CLpro, including caliciviruses and coronaviruses. Here, we report the development of the enzyme and cell-based assays for the 3CLpro of GI.1c/RHDV, recombinant GI.3P-GI.2 (RHDV2/b), and GII.1/European brown hare syndrome virus (EBHSV) as well as the identification of potent lagovirus 3CLpro inhibitors, including GC376, a protease inhibitor being developed for feline infectious peritonitis. In addition, structure-activity relationship study and homology modeling of the 3CLpro and inhibitors revealed that lagovirus 3CLpro share similar structural requirements for inhibition with other calicivirus 3CLpro. IMPORTANCE Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are viral diseases that affect lagomorphs with significant economic and ecological impacts. RHD vaccines are available, but specific antiviral treatment for these viral infections would be a valuable addition to the current control measures. Lagoviruses encode 3C-like protease (3CLpro), which is essential for virus replication and an attractive target for antiviral drug discovery. We have screened and identified potent small-molecule inhibitors that block lagovirus 3CLpro in the enzyme- and cell-based assays. Our results suggest that these compounds have the potential for further development as antiviral drugs for lagoviruses.

Monitoring of Rabbit Hemorrhagic Disease Virus in European Wild Rabbit (Oryctolagus cuniculus) Populations by PCR Analysis of Rabbit Fecal Pellets

European rabbits (Oryctolagus cuniculus) are affected by rabbit hemorrhagic disease (RHD), which is caused by a lagovirus responsible for significant mortality in European wild rabbit populations. Our study aimed to evaluate the potential for detecting viral RNA by duplex real-time PCR in rabbit fecal pellets collected in the field, as a noninvasive method to monitor RHD virus circulation in wild populations. To do this, monthly discoveries of rabbits that died from RHD and detection of viral RNA in fecal pellets were recorded in two enclosed populations of wild rabbits throughout a year. The results suggested a low performance of this procedure to monitor viral infection incidence and a weak concordance with monthly discoveries of rabbits that died from RHD. This poor association was probably due to the low amount of viral RNA in feces, the prolonged time of excretion after infection, and that the number of rabbits found dead from RHD does not necessarily correlate with RHD incidence. Nevertheless, this procedure may be a complementary noninvasive method to assist in determining the presence of RHD viruses in populations. Additional research is needed to determine the suitability of this methodology to perform epidemiologic surveys on wild populations of European rabbits and, especially, other European or North American lagomorph species affected by lagoviruses.

Outbreak of Rabbit Hemorrhagic Disease Virus 2 Infections, Ghana

In September 2019, high mortality in commercial rabbits was reported in the Greater Accra Region of Ghana. Rabbit hemorrhagic disease virus 2 phylogenetically related to isolates from 2015–2017 outbreaks in the Netherlands was confirmed as the causative agent. The virus has not yet been detected in native rabbits in Ghana.

Rabbit hemorrhagic disease virus type 2 epidemic in a rabbit colony in Japan

Twenty-three of 42 European rabbits (Oryctolagus cuniculus), belonging to the same rabbit colony, died in March 2020 (55% mortality) in Chiba prefecture, Japan. The disease course was extremely acute without indicators of death or hemorrhage. Necropsy revealed liver swelling, discoloration, cloudiness and fragility, and pulmonary edema. Histologically, severe hepatocellular necrosis (mainly peripheral) and intra-glomerular capillary hyalin thrombi were observed. On molecular-biological examination, reverse transcription polymerase chain reaction analysis of RNA from tissues detected a rabbit hemorrhagic disease virus, confirmed as a RHDV-2 VP60 fragment, which shared 99.42% nucleotide identity with the homologous fragment of RHDV-2 German isolate by nucleotide sequence analysis. This report shows the outbreak of rabbit hemorrhagic disease caused by RHDV-2, an emerging infectious disease, in Japan.

Myeloperoxidase and Lysozymes as a Pivotal Hallmark of Immunity Status in Rabbits

Simple Summary

Rabbit breeding is a very important element in the context of broadly understood industrial breeding, as rabbits are one of the main and most frequently chosen economic directions. Effective rabbit breeding, however, requires full control over the health of these animals, which is particularly related to the orientation regarding their immune status. There are many indicators that can be used to assess the immune system, but the greatest attention should be paid to those that change rapidly over time and reflect the body’s first line of defense. Peripheral blood granulocytes contain enzymes with strong antimicrobial properties, the level of which changes as a result of various external factors, e.g., viral infection, which was assessed in this study. The aim of the study was to evaluate the dynamics of myeloperoxidase (MPO) and lysozyme (LZM) in the experimental infection of rabbits with the Lagovirus europaeus/GI.1a virus, which is a pathogen causing high mortality, decimating rabbit farms all over the world in a short time. The results obtained in the dynamic system show that the levels of assessed enzymes significantly change in the blood during infection. Assessing the immune system using these indicators could therefore be a potential biomarker for the immune status of rabbits.

Abstract

Infectious diseases, due to their massive scale, are the greatest pain for all rabbit breeders. Viral infections cause enormous economic losses in farms. Treating sick rabbits is very difficult and expensive, so it is very important to prevent disease by vaccinating. In order to successfully fight viral infections, it is important to know about the immune response of an infected animal. The aim of this study was to analyze the immune response mediated by antimicrobial peptides (myeloperoxidase (MPO) and lysozyme (LZM)) in peripheral blood neutrophils and rabbit serum by non-invasive immunological methods. The study was carried out on mixed breed rabbits that were experimentally infected with two strains (Erfurt and Rossi) of the Lagovirus europaeus/GI.1a virus. It has been observed that virus infection causes changes in the form of statistically significant increases in the activity of MPO and LZM concentration, while in the case of LZM activity only statistically significant decreases were noted. Additionally, clinical symptoms typical for the course of the disease were noted, and the probability of survival of the animals at 60 h p.i. (post infection) was 30% for the Erfurt strain, and −60% for the Rossi strain. The obtained results of MPO and LZMs suggest that these enzymes, especially MPO, may serve as a prognostic marker of the state of the immune system of rabbits.

Rabbit Hemorrhagic Disease Virus Non-structural Protein 6 Induces Apoptosis in Rabbit Kidney Cells

Rabbit hemorrhagic disease (RHD) is a highly contagious disease caused by rabbit hemorrhagic disease virus (RHDV). Previous research has shown that RHDV induces apoptosis in numerous cell types, although the molecular mechanisms underlying the apoptosis induced by RHDV are not well understood. One possible factor is non-structural protein 6 (NSP6), a 3C-like protease that plays an important role in processing viral polyprotein precursors into mature non-structural proteins. To fully establish a role for NSP6, the present study examined the effects of ectopic expression of the protein in rabbit (RK13) and human (HeLa and HepG2) cells. We found that NSP6 suppressed cell viability and promoted apoptosis in all three cell types in a dose-dependent manner. We also identified increased caspase-3, -8, and -9 activities in RK13 cell, and an increased Bax to Bcl2 mRNA ratio. Mechanistically, the ability of NSP6 to induce apoptosis was impaired by mutation of the catalytic His27 residue. Our study has shown that RHDV NSP6 can induce apoptosis in host cells and is likely an important contributor to RHDV-induced apoptosis and pathogenesis.

Detection of Rabbit Hemorrhagic Disease Virus GI.2/RHDV2/b in the Mediterranean Pine Vole ( Microtus duodecimcostatus) and White-Toothed Shrew ( Crocidura russula)

The European wild rabbit ( Oryctolagus cuniculus) is a key prey species on the Iberian Peninsula, and several predator species that are at risk of extinction are dependent on them as prey. A new rabbit hemorrhagic disease (RHD) virus genotype (GI.2/RHDV2/b) emerged in 2010 and posed a threat to wild rabbit populations. During a survey aimed at investigating RHD epidemiology in wild rabbits, GI.2/RHDV2/b was detected by duplex real-time PCR in carcasses of one Mediterranean pine vole ( Microtus duodecimcostatus) and two white-toothed shrews ( Crocidura russula). Laboratory New Zealand white rabbits that were challenged with inocula obtained from the liver of the small mammals died showing RHD lesions, confirming the infectiousness of the isolates. Phylogenetic analysis of the VP60 gene nucleotide sequences showed complete homology between the isolates from the two small mammal species and a high degree of similarity, but not complete homology, to GI.2/RHDV2/b sequences from wild rabbits. The GI.2/RHDV2/b genotype has not been reported in species outside the order Lagomorpha.

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.

An Outbreak of Rabbit Hemorrhagic Disease in Finland

Rabbit hemorrhagic disease (RHD) was detected in European rabbits ( Oryctolagus cuniculus) for the first time ever in Finland in 2016. Reports of dead feral rabbits in Helsinki started to accumulate from April 2016. The Finnish Food Safety Authority Evira received the first animals in late April, and the main necropsy finding was severe, acute necrotizing hepatitis. Genetic material from RHD virus (RHDV) was detected in the liver and was further characterized as RHDV2. The Finnish virus did not group with RHDV strains from a concurrent outbreak in neighboring Sweden, suggesting another origin. The outbreak peaked in May and lasted until August, after which sightings of both live and dead rabbits became rare. No major outbreaks in domestic rabbits were observed, although infection in one pet rabbit was confirmed.

Host-Specific Glycans Are Correlated with Susceptibility to Infection by Lagoviruses, but Not with Their Virulence

Rabbit hemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV) are two lagoviruses from the family Caliciviridae that cause fatal diseases in two leporid genera, Oryctolagus and Lepus, respectively. In the last few years, several examples of host jumps of lagoviruses among leporids were recorded. In addition, a new pathogenic genotype of RHDV emerged, and many nonpathogenic strains of lagoviruses have been described. The molecular mechanisms behind host shifts and the emergence of virulence are unknown. Since RHDV uses glycans of the histo-blood group antigen type as attachment factors to initiate infection, we studied if glycan specificities of the new pathogenic RHDV genotype, nonpathogenic lagoviruses, and EBHSV potentially play a role in determining the host range and virulence of lagoviruses. We observed binding to A, B, or H antigens of the histo-blood group family for all strains known to primarily infect European rabbits (Oryctolagus cuniculus), which have recently been classified as GI strains. However, we could not explain the emergence of virulence, since similar glycan specificities were found in several pathogenic and nonpathogenic strains. In contrast, EBHSV, recently classified as GII.1, bound to terminal β-linked N-acetylglucosamine residues of O-glycans. Expression of these attachment factors in the upper respiratory and digestive tracts in three lagomorph species (Oryctolagus cuniculus, Lepus europaeus, and Sylvilagus floridanus) showed species-specific patterns regarding susceptibility to infection by these viruses, indicating that species-specific glycan expression is likely a major contributor to lagovirus host specificity and range.IMPORTANCE Lagoviruses constitute a genus of the family Caliciviridae comprising highly pathogenic viruses, RHDV and EBHSV, that infect rabbits and hares, respectively. Recently, nonpathogenic strains were discovered and new pathogenic strains have emerged. In addition, host jumps between lagomorphs have been observed. The mechanisms responsible for the emergence of pathogenicity and host species range are unknown. Previous studies showed that RHDV strains attach to glycans expressed in the upper respiratory and digestive tracts of rabbits, the likely portals of virus entry. Here, we studied the glycan-binding properties of novel pathogenic and nonpathogenic strains looking for a link between glycan binding and virulence or between glycan specificity and host range. We found that glycan binding did not correlate with virulence. However, expression of glycan motifs in the upper respiratory and digestive tracts of lagomorphs revealed species-specific patterns associated with the host ranges of the virus strains, suggesting that glycan diversity contributes to lagovirus host ranges.

Melatonin modulates the autophagic response in acute liver failure induced by the rabbit hemorrhagic disease virus

Autophagy is an important survival pathway and participates in the host response to infection. Beneficial effects of melatonin have been previously reported in an animal model of acute liver failure (ALF) induced by the rabbit hemorrhagic disease virus (RHDV). This study was aimed to investigate whether melatonin protection against liver injury induced by the RHDV associates to modulation of autophagy. Rabbits were infected with 2 × 10(4) hemagglutination units of a RHDV isolate and received 20 mg/kg melatonin at 0, 12, and 24 hr postinfection. RHDV induced autophagy, with increased expression of beclin-1, ubiquitin-like autophagy-related (Atg)5, Atg12, Atg16L1 and sequestrosome 1 (p62/SQSTM1), protein 1 light chain 3 (LC3) staining, and conversion of LC3-I to autophagosome-associated LC3-II. These effects reached a maximum at 24 hr postinfection, in parallel to extensive colocalization of LC3 and lysosome-associated membrane protein (LAMP)-1. The autophagic response induced by RHDV infection was significantly inhibited by melatonin administration. Melatonin treatment also resulted in decreased immunoreactivity for RHDV viral VP60 antigen and a significantly reduction in RHDV VP60 mRNA levels, oxidized to reduced glutathione ratio (GSSG/GSH), caspase-3 activity, and immunoglobulin-heavy-chain-binding protein (BiP) and CCAAT/enhancer-binding protein homologous protein (CHOP) expression. Results indicate that, in addition to its antioxidant and antiapoptotic effects, and the suppression of ER stress, melatonin induces a decrease in autophagy associated with RHDV infection and inhibits RHDV RNA replication. Results obtained reveal novel molecular pathways accounting for the protective effect of melatonin in this animal model of ALF.

Experimental Implantation Trials of Xenopsylla cunicularis Smit (Siphonaptera: Pulicidae) in Northern France with the Objective to Use it as Vaccine Vector

To combat animal diseases, we propose that Xenopsylla cunicularis Smit (Siphonaptera: Pulicidae), a specific flea of the European wild rabbit Oryctolagus cuniculus L. (Lagomorpha), can be used to carry a vaccine into wild rabbit populations to protect them against lethal diseases. Oryctolagus cuniculus is widespread throughout Europe, but X. cunicularis occurs naturally only in drier areas of Morocco, Spain, and southwestern France, raising questions about the flea's general use and the subsequent risk of uncontrolled proliferation outside its natural distribution. To evaluate this risk, fleas were released in five experimental enclosures containing rabbits (four in northern France and one in southwestern France as a control). Approximately one year later, adult and immature fleas were recovered from rabbits and warrens. The climate during the experiments was recorded and warren substrate granulometry was defined. Our results showed that northern France is not suitable for persistence of X. cunicularis because low temperatures reduce flea development and high rainfall all over the year keeps the soil damp, which is asphyxic for fleas, even on a sandy substrate. These implantation trials suggest that uncontrolled proliferation and permanent establishment of fleas are unlikely in northern France.

Codon optimization of the rabbit hemorrhagic disease virus (RHDV) capsid gene leads to increased gene expression in Spodoptera frugiperda 9 (Sf9) cells

Rabbit hemorrhagic disease (RHD) is contagious and highly lethal. Commercial vaccines against RHD are produced from the livers of experimentally infected rabbits. Although several groups have reported that recombinant subunit vaccines against rabbit hemorrhagic disease virus (RHDV) are promising, application of the vaccines has been restricted due to high production costs or low yield. In the present study, we performed codon optimization of the capsid gene to increase the number of preference codons and eliminate rare codons in Spodoptera frugiperda 9 (Sf9) cells. The capsid gene was then subcloned into the pFastBac plasmid, and the recombinant baculoviruses were identified with a plaque assay. As expected, expression of the optimized capsid protein was markedly increased in the Sf9 cells, and the recombinant capsid proteins self-assembled into virus-like particles (VLPs) that were released into the cell supernatant. Rabbits inoculated with the supernatant and the purified VLPs were protected against RHDV challenge. A rapid, specific antibody response against RHDV was detected by an ELISA in all of the experimental groups. In conclusion, this strategy of producing a recombinant subunit vaccine antigen can be used to develop a low-cost, insect cell-derived recombinant subunit vaccine against RHDV.

Oral immunization using tuber extracts from transgenic potato plants expressing rabbit hemorrhagic disease virus capsid protein

Rabbit hemorrhagic disease, which is caused by a calicivirus, is a lethal infection of adult animals that is characterized by acute liver damage and disseminated intravascular coagulation. In this study, we report the production of the major structural protein VP60 of rabbit hemorrhagic disease virus in transgenic tubers of potato plants and its use as an oral immunogen in rabbits.

In vitro translation of a subgenomic mRNA from purified virions of the Spanish field isolate AST/89 of rabbit hemorrhagic disease virus (RHDV)

Purified preparations of the Spanish field isolate of rabbit hemorrhagic disease virus AST/89 were found to contain the plus-stranded genomic RNA of more than 7.4 kilobases (kb) and large amounts of a subgenomic mRNA of 2.4 kb. The smaller RNA was translated in vitro and shown to code for a 60 kDa protein which was immunoprecipitated using anti-RHDV as well as anti-VP60 sera.