Haemorrhagic disease of lagomorphs: evidence for a calicivirus

The outbreak of rabbit hemorrhagic virus type 2 in the interior of China may be related to imported semen

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We identified one RHD case caused by a new RHDV variant (GI.2) in China through HA, TEM, and genome sequencing.

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This is the first study to demonstrate that GI.2 can replicate efficiently in the reproductive system.

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Our evidence suggests that GI.2 might be introduced into China by contaminated rabbit semen.

Immunity against Lagovirus europaeus and the Impact of the Immunological Studies on Vaccination

In the early 1980s, a highly contagious viral hemorrhagic fever in rabbits (Oryctolagus cuniculus) emerged, causing a very high rate of mortality in these animals. Since the initial occurrence of the rabbit hemorrhagic disease virus (RHDV), several hundred million rabbits have died after infection. The emergence of genetically-different virus variants (RHDV GI.1 and GI.2) indicated the very high variability of RHDV. Moreover, with these variants, the host range broadened to hare species (Lepus). The circulation of RHDV genotypes displays different virulences and a limited induction of cross-protective immunity. Interestingly, juvenile rabbits (<9 weeks of age) with an immature immune system display a general resistance to RHDV GI.1, and a limited resistance to RHDV GI.2 strains, whereas less than 3% of adult rabbits survive an infection by either RHDV GI.1. or GI.2. Several not-yet fully understood phenomena characterize the RHD. A very low infection dose followed by an extremely rapid viral replication could be simplified to the induction of a disseminated intravascular coagulopathy (DIC), a severe loss of lymphocytes—especially T-cells—and death within 36 to 72 h post infection. On the other hand, in animals surviving the infection or after vaccination, very high titers of RHDV-neutralizing antibodies were induced. Several studies have been conducted in order to deepen the knowledge about the virus’ genetics, epidemiology, RHDV-induced pathology, and the anti-RHDV immune responses of rabbits in order to understand the phenomenon of the juvenile resistance to this virus. Moreover, several approaches have been used to produce efficient vaccines in order to prevent an infection with RHDV. In this review, we discuss the current knowledge about anti-RHDV resistance and immunity, RHDV vaccination, and the further need to establish rationally-based RHDV vaccines.

Genotyping of rabbit hemorrhagic disease virus detected in diseased rabbits in Egyptian Provinces by VP60 sequencing

Background and Aim

Rabbit hemorrhagic disease (RHD) is an economically important disorder of rabbits, where infection results in severe losses to the meat and fur industries. Our goal was to characterize the RHD virus (RHDV) strains currently circulating in different regions of Egypt.

Materials and Methods

Fifty rabbits suspected of harboring RHDV from 15 Egyptian governorates were evaluated. Diseased rabbits were identified by clinical signs and postmortem lesions. RHDV was confirmed through hemagglutination assay (HA) and polymerase chain reaction (PCR). Partial sequencing of the VP60 gene was performed for genotyping.

Results

From 50 rabbits, we identified 16 cases of RHDV (32%) by HA and PCR, including seven males and nine females. We identified two distinct genotypes through sequencing of an amplified fragment of the virus VP60 gene. One group is composed of those circulating primarily in upper Egypt, which is closely related to the classical G3-G5 virus strains, and the second group, circulating predominantly in lower Egypt, was more closely related to the RHDV2 variant. The overall nucleotide sequence identity ranged from 78.4% to 100%, and identity with the vaccine strains ranged from 78.8% to 91.1%.

Conclusion

Our results constitute important documentation of RHDV strains currently circulating in Egypt. The findings suggest that there may be a limit to the effectiveness of currently applied vaccine strains as this formulation may not cover all circulating strains. A wider investigation that includes both domestic and wild rabbits will be needed to identify appropriate control measures for this disease.

Infection models of human norovirus: challenges and recent progress

Human norovirus (hNoV) infections cause acute gastroenteritis, accounting for millions of disease cases and more than 200,000 deaths annually. However, the lack of in vitro infection models and robust small-animal models has posed barriers to the development of virus-specific therapies and preventive vaccines. Promising recent progress in the development of a norovirus infection model is reviewed in this article, as well as attempts and efforts made since the discovery of hNoV more than 40 years ago. Because suitable experimental animal models for human norovirus are lacking, attractive alternatives are also discussed.

Viral Genome-Linked Protein (VPg) Is Essential for Translation Initiation of Rabbit Hemorrhagic Disease Virus (RHDV)

Rabbit hemorrhagic disease virus (RHDV), the causative agent of rabbit hemorrhagic disease, is an important member of the caliciviridae family. Currently, no suitable tissue culture system is available for proliferating RHDV, limiting the study of the pathogenesis of RHDV. In addition, the mechanisms underlying RHDV translation and replication are largely unknown compared with other caliciviridae viruses. The RHDV replicon recently constructed in our laboratory provides an appropriate model to study the pathogenesis of RHDV without in vitro RHDV propagation and culture. Using this RHDV replicon, we demonstrated that the viral genome-linked protein (VPg) is essential for RHDV translation in RK-13 cells for the first time. In addition, we showed that VPg interacts with eukaryotic initiation factor 4E (eIF4E) in vivo and in vitro and that eIF4E silencing inhibits RHDV translation, suggesting the interaction between VPg and eIF4E is involved in RHDV translation. Our results support the hypothesis that VPg serves as a novel cap substitute during the initiation of RHDV translation.

Immunogenicity of different recombinant rabbit hemorrhagic disease virus-like particles carrying CD8+ T cell epitope from chicken ovalbumin (OVA)

To explore the capacity and immunogenicity of virus-like particles (VLPs) of rabbit hemorrhagic disease virus (RHDV) accommodating foreign amino acid sequences, integrations were performed at the following four locations of the structural protein VP60 of RHDV using the OVA257-264 CD8+ T cell epitope (SIINFEKL): (1) inserting at the N-terminus of the VP60 protein (N1); (2) replacing amino acid positions 2-14 of the VP60 protein (N2); (3) replacing amino acid positions 196-207 of the VP60 protein (I1); and (4) replacing amino acid positions 217-228 of the VP60 protein (I2). The recombinant proteins were expressed by baculovirus expression system. The ability to form RHDV-like particles was confirmed by electron microscopy. The immunogenicity of the four recombinant proteins (N1, N2, I1 and I2) was evaluated in mice without any adjuvants. The results indicated that the four recombinant proteins (N1, N2, I1 and I2) could assemble into VLPs. All of the recombinant proteins could induce a specific immune response. Recombinant proteins I1 and I2 were able to elicit both high levels of IFN-γ secretion and anti-VP60 specific immune responses in the murine model. The levels of the VP60-specific IgG antibody in groups I1 and I2 displayed higher optical density (OD) values than those of groups N1 and N2 (P<0.001, P<0.001). The number of IFN-γ-producing splenocytes in mice that were immunized with recombinant proteins I1 and I2 was also significantly greater compared with mice that were immunized with recombinant proteins N1 and N2 (P<0.01). All of these above mentioned results might be beneficial to the establishment of the RHDV-VLPs display system.

Emergence of a new lagovirus related to Rabbit Haemorrhagic Disease Virus

Since summer 2010, numerous cases of Rabbit Haemorrhagic Disease (RHD) have been reported in north-western France both in rabbitries, affecting RHD-vaccinated rabbits, and in wild populations. We demonstrate that the aetiological agent was a lagovirus phylogenetically distinct from other lagoviruses and which presents a unique antigenic profile. Experimental results show that the disease differs from RHD in terms of disease duration, mortality rates, higher occurrence of subacute/chronic forms and that partial cross-protection occurs between RHDV and the new RHDV variant, designated RHDV2. These data support the hypothesis that RHDV2 is a new member of the Lagovirus genus. A molecular epidemiology study detected RHDV2 in France a few months before the first recorded cases and revealed that one year after its discovery it had spread throughout the country and had almost replaced RHDV strains. RHDV2 was detected in continental Italy in June 2011, then four months later in Sardinia.

An enhanced heterologous virus-like particle for human papillomavirus type 16 tumour immunotherapy

Cervical cancer is caused by high-risk, cancer-causing human papillomaviruses (HPV) and is the second highest cause of cancer deaths in women globally. The majority of cervical cancers express well-characterized HPV oncogenes, which are potential targets for immunotherapeutic vaccination. Here we develop a rabbit haemorrhagic disease virus (RHDV) virus-like particle (VLP)-based vaccine designed for immunotherapy against HPV16 positive tumours. An RHDV-VLP, modified to contain the universal helper T cell epitope PADRE and decorated with an MHC I-restricted peptide (aa 48–57) from the HPV16 E6, was tested for its immunotherapeutic efficacy against the TC-1 HPV16 E6 and E7-expressing tumour in mice. The E6-RHDV-VLP-PADRE was administered therapeutically for the treatment of a pre-existing TC-1 tumour and was delivered with antibodies either to deplete regulatory T cells (anti-CD25) or to block T cell suppression mediated through CTLA-4. As a result, the tumour burden was reduced by around 50% and the median survival time of mice to the humane endpoint was almost doubled the compared to controls. The incorporation of PADRE into the RHDV-VLP was necessary for an E6-specific enhancement of the anti-tumour response and the co-administration of the immune modifying antibodies contributed to the overall efficacy of the immunotherapy. The E6-RHDV-VLP-PADRE shows immunotherapeutic efficacy, prolonging survival for HPV tumour-bearing mice. This was enhanced by the systemic administration of immune-modifying antibodies that are commercially available for use in humans. There is potential to further modify these particles for even greater efficacy in the path to development of an immunotherapeutic treatment for HPV precancerous and cancer stages.

Virus-like particles and α-galactosylceramide form a self-adjuvanting composite particle that elicits anti-tumor responses

Virus-like particles (VLP) are effective vehicles for delivery of heterologous antigen to antigen-presenting cells. However VLP alone are insufficiently stimulatory to generate the signals required to facilitate effective priming of naïve T cells. We show that the VLP derived from rabbit hemorrhagic disease virus can bind the galactose-containing adjuvant α-galactosylceramide to form a composite particle for co-delivery of antigen and adjuvant to the same antigen-presenting cell. Vaccination with VLP and α-galactosylceramide activated splenic iNKT cells to produce IFN-γ and IL-4, led to the generation of antigen-specific T cells that protected prophylactically against subcutaneous tumor challenge, and was more effective at generating anti-tumor immune responses than either component individually. These data demonstrate a novel method for immunopotentiating VLP to increase their efficacy in the generation of anti-tumor responses via the innate ligand recognition properties of calicivirus-derived nanoparticles.

Rabbit haemorrhagic disease (RHD) and rabbit haemorrhagic disease virus (RHDV): a review

Rabbit haemorrhagic disease virus (RHDV) is a calicivirus of the genus Lagovirus that causes rabbit haemorrhagic disease (RHD) in adult European rabbits (Oryctolagus cuniculus). First described in China in 1984, the virus rapidly spread worldwide and is nowadays considered as endemic in several countries. In Australia and New Zealand where rabbits are pests, RHDV was purposely introduced for rabbit biocontrol. Factors that may have precipitated RHD emergence remain unclear, but non-pathogenic strains seem to pre-date the appearance of the pathogenic strains suggesting a key role for the comprehension of the virus origins. All pathogenic strains are classified within one single serotype, but two subtypes are recognised, RHDV and RHDVa. RHD causes high mortality in both domestic and wild adult animals, with individuals succumbing between 48-72 h post-infection. No other species has been reported to be fatally susceptible to RHD. The disease is characterised by acute necrotising hepatitis, but haemorrhages may also be found in other organs, in particular the lungs, heart, and kidneys due to disseminated intravascular coagulation. Resistance to the disease might be explained in part by genetically determined absence or weak expression of attachment factors, but humoral immunity is also important. Disease control in rabbitries relies mainly on vaccination and biosecurity measures. Such measures are difficult to be implemented in wild populations. More recent research has indicated that RHDV might be used as a molecular tool for therapeutic applications. Although the study of RHDV and RHD has been hampered by the lack of an appropriate cell culture system for the virus, several aspects of the replication, epizootology, epidemiology and evolution have been disclosed. This review provides a broad coverage and description of the current knowledge on the disease and the virus.

Review of companion animal viral diseases and immunoprophylaxis

In this article we review important established, newly emergent and potential viral diseases of cats, dogs and rabbits. Topics covered include virus epidemiology, disease pathogenesis, existing and prospective immunoprophylaxis against the viruses. For some feline viruses, notably the immunodeficiency virus, leukaemia virus and peritonitis virus, available vaccines are poorly efficacious but there are good prospects for this. A further challenge for the industry is likely to be due to viruses jumping species and the emergence of more virulent variants of established viruses resulting from mutations as has been the case for the canine parvovirus, coronaviruses and feline calicivirus.

Hyperlipidemia in rabbit hemorrhagic disease

Clinically healthy rabbits were inoculated with rabbit hemorrhagic disease virus (RHDV) and the kinetics of their serum lipid parameters and liver enzymes were monitored. After RHDV inoculation, hyperlipidemia was observed (P(triglyceride)<0.0001, P(cholesterol)=0.0003) along with significant increases in serum aspartate aminotransferase, alanine aminotransferase and gamma-glutamyltransferase (P<0.0001). An exponential increase in serum triglyceride was also seen. Thus, the presence of hyperlipidemia (from 30 h post-inoculation) in the infected rabbits points to impairment in lipid metabolism. This is the first demonstration that RHDV infection leads to hyperlipidemia, probably due to the disorder of liver enzymes associated with lipid metabolism.

Persistence of rabbit haemorrhagic disease virus genome in vaccinated rabbits after experimental infection

Rabbit haemorrhagic disease (RHD) is usually a fatal disease in rabbits which has spread rapidly across the continents. While previous studies suggested persistence in rabbits to be an important factor in the epidemiology, the relevance of field virus infection of immune rabbits has not been investigated in experimentally infected animals before. This report describes for the first time the persistence of rabbit haemorrhagic disease virus (RHDV) genome for at least 15 weeks in rabbits immunized with an inactivated vaccine as well as a subunit vaccine and subsequently challenged with virulent RHDV. The viral RNA loads were determined by real-time reverse transcription-polymerase chain reaction. No conspicuous association of the detectable amount of RHDV RNA with the type of vaccine, the time after infection and--with one exception--the level of RHDV-specific antibodies in the immunized animals was observed. The results presented in this study are an urgent evidence for the existence of carrier animals as an important factor in the epidemiology of RHD.

Severe leukopenia and liver biochemistry changes in adult rabbits after calicivirus infection

Calicivirus infection is the major cause of the severe decrease in the stocks of wild and farm rabbits that has occurred worldwide during the last two decades. Adult rabbits (10-weeks-old) were experimentally infected with a calicivirus inoculum that killed all animals by causing rabbit haemorrhagic disease (RHD) within 24-62 h of infection. The rabbits were used to evaluate blood cell numbers and serum biochemistry every 6h, starting 12h after the inoculation of the caliciviruses. No significant changes in blood parameters were observed in most of the rabbits up to 18 h of infection. Severe leukopenia was seen 6h before death of the infected rabbits; both heterophils and lymphocytes contributed to the decrease in circulating white blood cells. Platelets were also severely decreased in number. Marked enhancement in liver enzymes was seen 6-12 h before death of the infected rabbits. There was also evidence both for cholestasis, as expressed by the elevated levels of direct (conjugated) bilirubin, and for hypoglycemia, an alteration that it is likely to contribute for the seizures that rabbits show during the late stages of RHD. Liver ultrastructure of rabbits that died from RHD revealed extensive hepatocyte vacuolization, severe changes in mitochondrial structure, and depletion of glycogen granules. We conclude that: (i) severe leukopenia characterizes the final hours of calicivirus-induced RHD; (ii) hypoglycemia and cholestasis precede death of rabbits from RHD; (iii) the kinetics of liver enzymes allows an accurate prediction of the time of death of rabbits from calicivirus-induced RHD.

Transient decrease in blood heterophils and sustained liver damage caused by calicivirus infection of young rabbits that are naturally resistant to rabbit haemorrhagic disease

Young rabbits are naturally resistant to rabbit haemorrhagic disease (RHD) caused by the same calicivirus that kills, within 3 days, nearly all adult animals. We have investigated changes in blood leukocytes, and in the morphology and biochemistry of the liver (the organ where caliciviruses replicate) of young rabbits undergoing benign infection by the RHD virus. Four-week-old rabbits were infected with a calicivirus inoculum having a titre of 2(12) haemagglutination units either sacrificed 18, 24, 48 and 72 h later, or kept for follow-up studies up to 21 days after inoculation. The infection caused an acute and transient decrease in blood heterophils, and sustained enhancement in hepatic transaminases. Inflammatory infiltrates of the liver were seen in all animals after 24 h of infection; they had a predominant midlobular location. Hepatocytes could present different degrees of cell damage, including cell death; these lesions were limited to the liver cells located around the inflammatory infiltrates. Liver transaminases peaked 24-48 h after calicivirus infection; this was the same timing when liver infiltration and hepatocyte damage were more evident. No alterations of other parameters of liver biochemistry were observed. We conclude that calicivirus infection of young rabbits causes a subclinical disorder characterised by an acute and transient decrease in circulating heterophils, and focal liver damage that is expressed by intralobular infiltration by heterophils, initially, and, later on, by mononuclear cells. Our finding of persistence of increased values of liver transaminases suggests chronicity of the infection in young rabbits. We propose that, although resistant to RHD, young rabbits infected by calicivirus may be long-term carriers of the infectious agent and, thus, become a major source of transmission of the virus.

Binding of rabbit hemorrhagic disease virus to antigens of the ABH histo-blood group family

The ability of rabbit hemorrhagic disease virus to agglutinate human erythrocytes and to attach to rabbit epithelial cells of the upper respiratory and digestive tracts was shown to depend on the presence of ABH blood group antigens. Indeed, agglutination was inhibited by saliva from secretor individuals but not from nonsecretors, the latter being devoid of H antigen. In addition, erythrocytes of the rare Bombay phenotype, which completely lack ABH antigens, were not agglutinated. Native viral particles from extracts of infected rabbit liver as well as virus-like particles from the recombinant virus capsid protein specifically bound to synthetic A and H type 2 blood group oligosaccharides. Both types of particles could attach to adult rabbit epithelial cells of the upper respiratory and digestive tracts. This binding paralleled that of anti-H type 2 blood group reagents and was inhibited by the H type 2-specific lectin UEA-I and polyacrylamide-conjugated H type 2 trisaccharide. Young rabbit tissues were almost devoid of A and H type 2 antigens, and only very weak binding of virus particles could be obtained on these tissues.

Experimental infections of rabbits with rabbit haemorrhagic disease virus monitored by polymerase chain reaction

Adult and 4-5-week-old rabbits were inoculated subcutaneously with rabbit haemorrhagic disease virus (RHDV). Samples were prepared from various tissues at intervals postinoculation (PI) for the detection of viral RNA and antigens. Using a haemagglutination test (HAT), viral antigens were detected in the liver, bile and spleen of the adult rabbits at and after 36 h PI. The reverse transcription-polymerase chain reaction (RT - PCR) showed that RHDVRNA was present in the liver, bile and spleen as early as 18 hours PI, whereas lung, kidney, thymus, mesenteric lymph node and buffy coat were found to be positive after more than 26 hours PI. In addition, viral RNA in urine and faeces showed a variable positivity at and after 36 hours PI. In the young rabbits, RT - PCR showed that RHDVRNA was present as early as 1 day PI in the liver, bile, spleen and buffy coat; whereas lung, kidney, thymus, mesenteric lymph node and faeces were found to be positive at and after 2 days PI. Bile and spleen were the only samples in which viral RNA was detected throughout the length of the experiment. Virus was not reactivated in six recovered virus-inoculated rabbits treated with dexamethasone or a classical swine fever virus vaccine. Using a haemagglutination inhibition test and an ELISA, antibody titres increased rapidly from one week PI onwards, peaked at approximately three weeks of age, and were maintained throughout the length of the experiment.

Detection and preliminary characterization of a new rabbit calicivirus related to rabbit hemorrhagic disease virus but nonpathogenic

A new rabbit calicivirus related to the rabbit hemorrhagic disease virus (RHDV) was identified. The new virus contains significant differences from the previously characterized RHDV isolates in terms of pathogenicity, viral titer, tropism, and primary sequence of the structural protein. Cross-protection experiments, antigenic data, and sequence comparisons demonstrate that the new virus is more closely related to RHDV than to the European brown hare syndrome virus, another member of the caliciviruses of the lagomorph group. The existence of a nonpathogenic calicivirus, which we propose to name rabbit calicivirus (RCV), provides an explanation for the early discrepancies found in the course of serological surveys of the rabbit population in European countries.

Sensitive detection of human Caliciviridae by RT-PCR

A semi-nested reverse transcriptase-polymerase chain reaction (RT-PCR) was developed for the detection of human Caliciviridae. The method was evaluated on faecal samples from patients with gastroenteritis sent to the Norwegian National Institute of Public Health for routine diagnosis by direct electron microscopy (EM). Of 166 samples, 49 were found to contain Caliciviridae by EM, while 7 samples contained other viruses. A total of 74 samples was positive by PCR, including all the samples with EM detectable Caliciviridae, while specimens containing other agents were negative. Phylogenetic analysis of RNA sequences from 14 Norwegian samples indicated that the viruses present in Norway are evenly distributed when compared to sequences of human Caliciviridae from other countries. The PCR primers should therefore be useful for samples from other regions. The phylogenetic analysis did not cluster viruses with a calici-like morphology, but mingled them with sequences from Norwalk-like viruses, indicating that the two morphological types do not represent separate genogroups.

Diagnosis of rabbit haemorrhagic disease (RHD) and European brown hare syndrome (EBHS) by indirect sandwich polyclonal ELISA

The establishment of two indirect sandwich polyclonal ELISAs for the virological diagnosis of rabbit haemorrhagic disease (RHD) and European brown hare syndrome (EBHS) is described. Each assay uses rabbit and guinea pig antisera raised to RHD or EBHS purified virus particles. The tests are sensitive and specific, but cross-reactions between rabbit haemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV) are observed. Most rabbit liver homogenates identified as RHDV-positive by ELISA do not haemagglutinate human red blood cells at room temperature.

Early stages of rabbit haemorrhagic disease virus infection monitored by polymerase chain reaction

In order to define more accurately the initial events that take place during rabbit haemorrhagic disease virus (RHDV) infection, different organs of experimentally infected rabbits were analysed for the presence of the virus and correlated with histopathological observations. A total of 24 rabbits were intranasally inoculated with a viral suspension, and tissue samples were taken from the liver, spleen, kidney, lung, thymus, lymph node and tonsil at different intervals post-inoculation (2, 4, 6, 12, 18, 24, 30, 36, 48, 50, 51, 70 and 72 h). Histopathological observations revealed the presence of the first significant lesions at 30 h post-inoculation (p.i.) in the liver. Using an ELISA and a haemagglutination test (HAT), the virus was detected in the liver at 36 h p.i. The reverse transcriptase-polymerase chain reaction (RT-PCR) showed that the RHDV RNA was present as early as 18 h p.i. in the liver and spleen, whereas thymus, kidney, tonsil and lymph node were found to be positive after more than 36 h p.i. The lungs presented a variable positivity between 0 and 36 h p.i., but remained positive after this time.

Identification of the virus of rabbit haemorrhagic disease in Tunisia

During 1992 and 1993, outbreaks of an acute, highly fatal disease mainly affecting adult rabbits were observed in Tunisia. The clinical and pathological findings were consistent with rabbit haemorrhagic disease. A monoclonal antibody designated PG4G3 specific for surface determinants of the rabbit haemorrhagic disease virus was used to identify the aetiological agent by ELISA and by colloidal gold immunoelectron microscopy; a haemagglutination test and conventional immunoelectron microscopy were also used. The results confirmed the first recorded cases of the disease in Tunisia.

Antigenicity of the rabbit hemorrhagic disease virus studied by its reactivity with monoclonal antibodies

A panel of anti-rabbit hemorrhagic disease virus (anti-RHDV) monoclonal antibodies was produced and characterized. The ability of the MAbs to recognize epitopes present on RHDV capsids, European brown hare syndrome virus capsids and RHDV subunits was determined. Preliminary results on the neutralizing capacity of the MAbs were obtained by in vivo protection experiments. The antigenic map of RHDV obtained by this study is consistent with the current models of the calicivirus structure.

Detection of antibodies to rabbit haemorrhagic disease virus: an immunoblotting method using virus-coated human erythrocyte membranes

The virus of rabbit haemorrhagic disease (RHDV) was purified from infected rabbit liver homogenate by using its property to bind to human red blood cells. Lysates from virus coated cells contained a 60 kDa protein identified as the major viral protein. Immunoblots prepared with that preparation were proved to be useful for immunochemical analysis since the 60 kDa component was intensively stained by subsequent incubation with rabbit sera from infected rabbits and with a secondary labelled antibody. The sera from 114 rabbits were analysed with this test and the data were compared with those obtained by using the haemagglutination inhibition test (HIT). Among the 114 field sera tested by Western blot, 86 contained antibodies to the 60 kDa RHDV antigen whereas only 76 showed positive reaction by HIT. The sensitivity and the specificity of the Western blot were 0.85 and 0.45, respectively, with a concordance between the two techniques of 0.72. Additionally, the European brown hare syndrome virus antibodies reacted with the 60 kDa RHDV protein on immunoblots.

Sequence similarity of human caliciviruses and small round structured viruses

The application of reverse transcription-polymerase chain reaction (RT-PCR) using primers directed to the RNA dependent RNA polymerase region within ORF1 of Norwalk virus (NV) showed that 31 percent of morphologically typical human caliciviruses (HuCV) and 57% of small round structured viruses (SRSVs) produced a product of 470 bp similar to the NV control, NV 8FIIa/68/US. Alignment of the amino acid sequences of morphologically typical HuCVs with previously published sequences for SRSVs, NV, and Snow Mountain agent (SMA) showed a high degree of homology (90-92%) with SMA and a lesser extent of homology with NV (60-61%). The amino acid sequence of two strains of HuCV, HuCV/3C/92/UK, and HuCV/5C/92/UK differed by only one or two amino acids respectively in the RNA dependent RNA polymerase region from that of two strains of SRSV obtained from children in the United Kingdom, SRSV/4S/90/UK and Japan, SRSV/OTH-25/89/J which were found to have identical amino acid sequences. The use of an EIA for detection of NV antigen employing antisera raised to recombinant NV protein indicated that HuCVs and SRSVs obtained from children and adults in the United Kingdom were antigenically distinct from the prototype Norwalk virus, NV/8fIIa/68/US.

Morphologic and immunohistochemical characterization of the hepatic lesions associated with European brown hare syndrome

Liver lesions were studied in 40 free-living adult European brown hares (Lepus europaeus) and varying hares (Lepus timidus) of both sexes that had died in Sweden with the viral infection European brown hare syndrome (EBHS). The lesions were characterized by their histopathologic, immunohistochemical, and electron microscopic findings. Periportal to massive coagulation necrosis was a distinctive feature of EBHS. Lytic necrosis, inflammation, fatty degeneration, and cholangitis occurred variably. Accumulation of basophilic granules in the cytoplasm of hepatocytes was commonly observed; these lesions corresponded ultrastructurally to mitochondrial calcification. Viral antigen was revealed in the cytoplasm and nucleus of hepatocytes and in the cytoplasm of macrophages.