MicroRNAs participate in the regulation of apoptosis and oxidative stress-related gene expression in rabbits infected with Lagovirus europaeus GI.1 and GI.2 genotypes

MicroRNAs (miRs) are a group of small, 17-25 nucleotide, non-coding RNA that regulate gene expression at the post-transcriptional level. To date, little is known about the molecular signatures of regulatory interactions between miRs and apoptosis and oxidative stress in viral diseases. Lagovirus europaeus is a virus that causes severe disease in rabbits (Oryctolagus cuniculus) called Rabbit Hemorrhagic Disease (RHD) and belongs to the Caliciviridae family, Lagovirus genus. Within Lagovirus europaeus associated with RHD, two genotypes (GI.1 and GI.2) have been distinguished, and the GI.1 genotype includes four variants (GI.1a, GI.1b, GI.1c, and GI.1d). The study aimed to assess the expression of miRs and their target genes involved in apoptosis and oxidative stress, as well as their potential impact on the pathways during Lagovirus europaeus-two genotypes (GI.1 and GI.2) infection of different virulences in four tissues (liver, lung, kidneys, and spleen). The expression of miRs and target genes related to apoptosis and oxidative stress was determined using quantitative real-time PCR (qPCR). In this study, we evaluated the expression of miR-21 (PTEN, PDCD4), miR-16b (Bcl-2, CXCL10), miR-34a (p53, SIRT1), and miRs-related to oxidative stress-miR-122 (Bach1) and miR-132 (Nfr-2). We also examined the biomarkers of both processes (Bax, Bax/Bcl-2 ratio, Caspase-3, PARP) and HO-I as biomarkers of oxidative stress. Our report is the first to present the regulatory effects of miRs on apoptosis and oxidative stress genes in rabbit infection with Lagovirus europaeus-two genotypes (GI.1 and GI.2) in four tissues (liver, lungs, kidneys, and spleen). The regulatory effect of miRs indicates that, on the one hand, miRs can intensify apoptosis (miR-16b, miR-34a) in the examined organs in response to a viral stimulus and, on the other hand, inhibit (miR-21), which in both cases may be a determinant of the pathogenesis of RHD and tissue damage. Biomarkers of the Bax and Bax/Bcl-2 ratio promote more intense apoptosis after infection with the Lagovirus europaeus GI.2 genotype. Our findings demonstrate that miR-122 and miR-132 regulate oxidative stress in the pathogenesis of RHD, which is associated with tissue damage. The HO-1 biomarker in the course of rabbit hemorrhagic disease indicates oxidative tissue damage. Our findings show that miR-21, miR-16b, and miR-34a regulate three apoptosis pathways. Meanwhile, miR-122 and miR-132 are involved in two oxidative stress pathways.

Biomarkers of the Complement System Activation (C3a, C5a, sC5b-9) in Serum of Patients before and after Liver Transplantation

The liver has a huge impact on the functioning of our body and the preservation of homeostasis. It is exposed to many serious diseases, which may lead to the chronic failure of this organ, which is becoming a global health problem today. Currently, the final form of treatment in patients with end-stage (acute and chronic) organ failure is transplantation. The proper function of transplanted organs depends on many cellular processes and immune and individual factors. An enormous role in the process of acceptance or rejection of a transplanted organ is attributed to, among others, the activation of the complement system. The aim of this study was the evaluation of the concentration of selected biomarkers' complement system activation (C3a, C5a, and sC5b-9 (terminal complement complex)) in the serum of patients before and after liver transplantation (24 h, two weeks). The study was conducted on a group of 100 patients undergoing liver transplantation. There were no complications during surgery and no transplant rejection in any of the patients. All patients were discharged home 2-3 weeks after the surgery. The levels of all analyzed components of the complement system were measured using the ELISA method. Additionally, the correlations of the basic laboratory parameters-C-reactive protein (CRP), hemoglobin (Hb), total bilirubin, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGTP), and albumin-with the parameters of the complement system (C3a, C5a, and sC5b-9) were determined. In our study, changes in the concentrations of all examined complement system components before and after liver transplantation were observed, with the lowest values before liver transplantation and the highest concentration two weeks after. The direct increase in components of the complement system (C3a, C5a, and sC5b-9) 24 h after transplantation likely affects liver damage after ischemia-reperfusion injury (IRI), while their increase two weeks after transplantation may contribute to transplant tolerance. Increasingly, attention is being paid to the role of C3a and CRP as biomarkers of damage and failure of various organs. From the point of view of liver transplantation, the most interesting correlation in our own research was found exactly between CRP and C3a, 24 h after the transplantation. This study shows that changes in complement activation biomarkers and the correlation with CRP in blood could be a prognostic signature of liver allograft survival or rejection.

Digital PCR (dPCR) Quantification of miR-155-5p as a Potential Candidate for a Tissue Biomarker of Inflammation in Rabbits Infected with Lagovirus europaeus/Rabbit Hemorrhagic Disease Virus (RHDV)

MicroRNAs (miRNAs, miRs) are a group of small, 17-25 nucleotide, non-coding RNA sequences that, in their mature form, regulate gene expression at the post-transcriptional level. They participate in many physiological and pathological processes in both humans and animals. One such process is viral infection, in which miR-155 participates in innate and adaptive immune responses to a broad range of inflammatory mediators. Recently, the study of microRNA has become an interesting field of research as a potential candidate for biomarkers for various processes and disease. To use miRNAs as potential biomarkers of inflammation in viral diseases of animals and humans, it is necessary to improve their detection and quantification. In a previous study, using reverse transcription real-time quantitative PCR (RT-qPCR), we showed that the expression of ocu-miR-155-5p in liver tissue was significantly higher in rabbits infected with Lagovirus europaeus/Rabbit Hemorrhagic Disease Virus (RHDV) compared to healthy rabbits. The results indicated a role for ocu-miR-155-5p in Lagovirus europaeus/RHDV infection and reflected hepatitis and the impairment/dysfunction of this organ during RHD. MiR-155-5p was, therefore, hypothesized as a potential candidate for a tissue biomarker of inflammation and examined in tissues in Lagovirus europaeus/RHDV infection by dPCR. The objective of the study is the absolute quantification of ocu-miR-155-5p in four tissues (liver, lung, kidney, and spleen) of rabbits infected with Lagovirus europaeus/RHDV by digital PCR, a robust technique for the precise and direct quantification of small amounts of nucleic acids, including miRNAs, without standard curves and external references. The average copy number/µL (copies/µL) of ocu-miRNA-155-5p in rabbits infected with Lagovirus europaeus GI.1a/Rossi in the liver tissue was 12.26 ± 0.14, that in the lung tissue was 48.90 ± 9.23, that in the kidney tissue was 16.92 ± 2.89, and that in the spleen was 25.10 ± 0.90. In contrast, in the tissues of healthy control rabbits, the average number of copies/µL of ocu-miRNA-155-5p was 5.07 ± 1.10 for the liver, 23.52 ± 2.77 for lungs, 8.10 ± 0.86 for kidneys, and 42.12 ± 3.68 for the spleen. The increased expression of ocu-miRNA-155-5p in infected rabbits was demonstrated in the liver (a fold-change of 2.4, p-value = 0.0003), lung (a fold-change of 2.1, p-value = 0.03), and kidneys (a fold-change of 2.1, p-value = 0.01), with a decrease in the spleen (a fold-change of 0.6, p-value = 0.002). In the study of Lagovirus europaeus/RHDV infection and in the context of viral infections, this is the first report that shows the potential use of dPCR for the sensitive and absolute quantification of microRNA-155-5p in tissues during viral infection. We think miR-155-5p may be a potential candidate for a tissue biomarker of inflammation with Lagovirus europaeus/RHDV infection. Our report presents a new path in discovering potential candidates for the tissue biomarkers of inflammation.

Improved RAPD Method for Candida parapsilosis Fingerprinting

Recently, methods based on the analysis of arbitrarily amplified target sites of genome microorganisms have been extensively applied in microbiological studies, and especially in epidemiological studies. The range of their application is limited by problems with discrimination and reproducibility resulting from a lack of standardized and reliable methods of optimization. The aim of this study was to obtain optimal parameters of the Random Amplified Polymorphic DNA (RAPD) reaction by using an orthogonal array as per the Taguchi and Wu protocol, modified by Cobb and Clark for Candida parapsilosis isolates. High Simpson’s index values and low Dice coefficients obtained in this study indicated a high level of interspecies DNA polymorphism between C. parapsilosis strains, and the optimized RAPD method proved useful in the microbiological and epidemiological study.

Evaluation of the Influence of Biological Factors during the Course of Treatment in Patients with Ovarian Cancer

The aim of this study was to evaluate the influence of β-endorphins and serotonin on the course of treatment, disease-free time, and overall survival of patients with ovarian cancer. This study may contribute to the identification of modifiable factors that may influence the treatment of ovarian cancer. The research was carried out in a group of 162 patients of which 139 respondents were included in the research; ovarian cancer was diagnosed in 78 of these patients. The study consisted of three stages. In the first stage of diagnostics, a survey among the patients was carried out. In the second stage-5 mL of blood was collected from each patient (n = 139) in the preoperative period to determine the concentration of β-endorphin and serotonin. In the third stage-blood samples were collected from those patients who had completed chemotherapy treatment or had surgery. Concentrations of β-endorphin and serotonin were measured by the Luminex method, using the commercial Luminex Human Discovery Assay kit. The average age of the patients was 62.99 years. The level of β-endorphin significantly differs among patients diagnosed with ovarian cancer and among patients in the control group (202.86; SD-15.78 vs. 302.00; SD-24.49). A lower level of β-endorphins was found in the patients with a recurrence of the neoplastic process compared to those without recurrence (178.84; SD-12.98 vs. 205.66; SD-13.37). On the other hand, the level of serotonin before chemotherapy was higher in the group of people with disease recurrence compared to those without recurrence (141.53; SD-15.33 vs. 134.99; SD-10.08). Statistically significantly positive correlations were found between the level of β-endorphin and both disease-free time (β-endorphin levels before chemotherapy: rho Spearman 0.379, p < 0.027; β-endorphin levels after chemotherapy: rho Spearman 0.734 p < 0.001) and survival time (β-endorphin levels before chemotherapy: rho Spearman 0.267, p < 0.018; β-endorphin levels after chemotherapy: rho Spearman 0.654 p < 0.001). 1. The levels of serotonin and β-endorphin levels are significantly related to ovarian cancer and change during treatment. 2. High mean preoperative concentrations of β-endorphins were significantly related to overall survival and disease-free time.

New Insights into the Role of the Complement System in Human Viral Diseases

The complement system (CS) is part of the human immune system, consisting of more than 30 proteins that play a vital role in the protection against various pathogens and diseases, including viral diseases. Activated via three pathways, the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP), the complement system leads to the formation of a membrane attack complex (MAC) that disrupts the membrane of target cells, leading to cell lysis and death. Due to the increasing number of reports on its role in viral diseases, which may have implications for research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this review aims to highlight significant progress in understanding and defining the role of the complement system in four groups of diseases of viral etiology: (1) respiratory diseases; (2) acute liver failure (ALF); (3) disseminated intravascular coagulation (DIC); and (4) vector-borne diseases (VBDs). Some of these diseases already present a serious global health problem, while others are a matter of concern and require the collaboration of relevant national services and scientists with the World Health Organization (WHO) to avoid their spread.

Changes in MicroRNA Expression during Rabbit Hemorrhagic Disease Virus (RHDV) Infection

Current knowledge on the role of microRNAs (miRNAs) in rabbit hemorrhagic disease virus (RHDV) infection and the pathogenesis of rabbit hemorrhagic disease (RHD) is still limited. RHDV replicates in the liver, causing hepatic necrosis and liver failure. MiRNAs are a class of short RNA molecules, and their expression profiles vary over the course of diseases, both in the tissue environment and in the bloodstream. This paper evaluates the expression of miRNAs in the liver tissue (ocu-miR-122-5p, ocu-miR-155-5p, and ocu-miR-16b-5p) and serum (ocu-miR-122-5p) of rabbits experimentally infected with RHDV. The expression levels of ocu-miR-122-5p, ocu-miR-155-5p, and ocu-miR-16b-5p in liver tissue were determined using reverse transcription quantitative real-time PCR (RT-qPCR), and the expression level of circulating ocu-miR-122-5p was established using droplet digital PCR (ddPCR). The expression levels of ocu-miR-155-5p and ocu-miR-16b-5p were significantly higher in the infected rabbits compared to the healthy rabbits (a fold-change of 5.8 and 2.5, respectively). The expression of ocu-miR-122-5p was not significantly different in the liver tissue from the infected rabbits compared to the healthy rabbits (p = 0.990), while the absolute expression level of the circulating ocu-miR-122-5p was significantly higher in the infected rabbits than in the healthy rabbits (p < 0.0001). Furthermore, a functional analysis showed that ocu-miR-155-5p, ocu-miR-16b-5p, and ocu-miR-122-5p can regulate the expression of genes involved in processes correlated with acute liver failure (ALF) in rabbits. Search tool for the retrieval of interacting genes/proteins (STRING) analysis showed that the potential target genes of the three selected miRNAs may interact with each other in different pathways. The results indicate the roles of these miRNAs in RHDV infection and over the course of RHD and may reflect hepatic inflammation and impairment/dysfunction in RHD.

Genetic variability and phylogenetic analysis of Lagovirus europaeus strains GI.1 (RHDV) and GI.2 (RHDV2) based on the RNA-dependent RNA polymerase (RdRp) coding gene

Lagovirus europaeus GI.1 (RHDV-rabbit haemorrhagic disease virus) and GI.2 (RHDV2-rabbit haemorrhagic disease virus 2), family Caliciviridae, genus Lagovirus, are etiological factors of the rabbit haemorrhagic disease (RHD). This small RNA virus is a great model for tracking the variability and evolution of RNA viruses, because it uses an RNA-dependent RNA polymerase (RdRp) to replicate its own genetic material. This polymerase determines the fidelity and the rates of replication and mutation of the virus, conditioning its adaptation to the environment and even to a new host, and thus influencing evolution of the virus. The aim of this study was to determine the genetic variability and phylogenetic relationships of 105 Lagovirus europaeus strains with different genotypes based on the RdRp gene. The strains came from around the world in the years of 1987-2017. The aforementioned group of 105 strains included 14 strains whose RdRp sequences were obtained and analysed in this study, and the rest were retrieved from GenBank: 74 strains classified as genotype GI.1 (RHDV), 14 as GI.2 (RHDV2), 2 strains of Lagovirus europaeus not assigned to any genotype, and a MRCV strain, the sequences of which were collected from GenBank. Among the 14 strains whose RdRp sequences were obtained in this study, the highest variability was presented in the Austrian 237 strain from 2004. The genetic distance between the Austrian 237 strain and the remaining thirteen analysed strains ranged from 0.117 to 0.123 (from 11.7% to 12.3% nucleotide substitutions). The lowest variability, however, was recorded for Hungarian, Czech and Austrian strains. On the phylogenetic tree, the 14 analysed strains were allocated into GI.1c (G2), GI.1d (G3-G5) and GI.1a (RHDVa). Analysis of the genetic variability of the 105 strains of Lagovirus europaeus indicated a growing genetic distance between the strains, both in time and location. Phylogenetic analysis showed a division of the strains into seven groups, dictated by the chronology, geographical location and evolutionary events in the history of the virus, such as mutations and recombinations.

Proposal for a unified classification system and nomenclature of lagoviruses

Lagoviruses belong to the Caliciviridae family. They were first recognized as highly pathogenic viruses of the European rabbit (Oryctolagus cuniculus) and European brown hare (Lepus europaeus) that emerged in the 1970-1980s, namely, rabbit haemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV), according to the host species from which they had been first detected. However, the diversity of lagoviruses has recently expanded to include new related viruses with varying pathogenicity, geographic distribution and host ranges. Together with the frequent recombination observed amongst circulating viruses, there is a clear need to establish precise guidelines for classifying and naming lagovirus strains. Therefore, here we propose a new nomenclature based on phylogenetic relationships. In this new nomenclature, a single species of lagovirus would be recognized and called Lagovirus europaeus. The species would be divided into two genogroups that correspond to RHDV- and EBHSV-related viruses, respectively. Genogroups could be subdivided into genotypes, which could themselves be subdivided into phylogenetically well-supported variants. Based on available sequences, pairwise distance cutoffs have been defined, but with the accumulation of new sequences these cutoffs may need to be revised. We propose that an international working group could coordinate the nomenclature of lagoviruses and any proposals for revision.

Values of apoptosis of lymphocytes and granulocytes in peripheral blood of Polish mixed-breed rabbits in the annual cycle

The objective of the study was to determine values of apoptosis for peripheral blood lymphocytes and granulocytes, including dependency on the season of the year, in Polish mixed-breed rabbits and in mixed-breed rabbits with the addition of blood of meat-breed rabbits. The study was carried out in four seasons of the year (spring, summer, autumn, winter) involving 120 Polish mixed-breed rabbits - group I, and 120 Polish mixed-breed rabbits with addition of meat-breed rabbit blood - group II. Assessment of apoptosis of lymphocytes and granulocytes was performed using as FACScan cytometer by Becton Dickinson with FACSDiva software (USA), using as ApoFluor® Green Caspase reagent kit (MP Biomedicals, USA) to detect the activity of the total caspase pool 1, 3, 4, 5, 6, 7, 8, 9 in granulocytes and lymphocytes of rabbit peripheral blood. The results for apoptosis of lymphocytes and granulocytes in peripheral blood in the animals investigated (group I and II) were subjected to statistical analysis with the t'Student test at p=0.05. It was noted that, in rabbits from group I, the values for apoptosis of lymphocytes were the highest in winter and autumn (36.02% and 31.24%, respectively), and the lowest in spring and summer (26.73% and 22.72%, respectively), whereas in the case of granulocytes the highest values were in summer and spring (14.69% and 12.95%, respectively), and the lowest in winter and autumn (8.16% and 8.57%, respectively). In mixed-breed rabbits with the addition of meat-breed blood (group II), the values for apoptosis of lympocytes were the highest in spring (29.13%), and the lowest in summer (25.43%); whereas in the case of granulocytes the highest values were in summer and spring (14.0% and 11.15%, respectively), and the lowest in autumn and winter (7.46% and 7.64%, respectively).

Hematological parameters in Polish mixed breed rabbits with addition of meat breed blood in the annual cycle

In the paper we studied haematologic values, such as haemoglobin concentration, haematocrit value, thrombocytes, leucocytes: lymphocytes, neutrophils, basophils, eosinophils and monocytes in the pheral blood in Polish mixed-breeds with addition of meat breed blood in order to obtain the reference values which are until now not available for this animals. In studying this indices we took into consideration the impact of the season (spring, summer, autumn, winter), and sex of the animals. The studies have shown a high impact of the season of the year on those rabbits, but only in spring and summer. Moreover we observed that the sex has mean impact on the studied values of haematological parameters in those rabbits. According to our knowledge, this is the first paper on haematologic values in this widely used group of rabbits, so they may serve as reference values.

Natural immunity factors in Polish mixed breed rabbits

Mixed-breed rabbits in Poland are widely used for diagnostic and scientific research and as utility animals, therefore there is a need to know their immunological status, as well as their haematological status. In this study natural immunity factors were analyzed in Polish mixed-breed rabbits and Polish mixed-breed rabbits with addition of blood of meet-breed, considering the impact of sex and season of the year (spring, summer, autumn, winter) using measurement of non-specific cellular and humoral immunity parameters in peripheral blood. The study has revealed that there is a variety between the two commonly used mixed-breed types of rabbits, especially when sex and season is concerned, which is crucial for using these animals in experiments.

Apoptosis of peripheral blood leucocytes in rabbits infected with different strains of rabbit haemorrhagic disease virus

The pathogenicity of RHDV (rabbit haemorrhagic disease virus) is mainly associated with its affinity to blood vessels, with causing disseminated intravascular coagulations (DIC), and with the stimulation of the host immune system. Moreover, there are implications suggesting that apoptosis may be a pivotal process in understanding the basis of viral haemorrhagic disease in rabbits - a serious infectious disease causing mortality to wild and domestic rabbits. The aim of this study is to evaluate, by means of flow cytometry, the dynamics of apoptosis in peripheral blood granulocytes and lymphocytes in rabbits experimentally infected with seven different strains of RHDV and so-called antigenic variants of RHDV denominated as RHDVa, i.e.: Hungarian 24V/89, 1447V/96, 72V/2003; Austrian 01-04, 237/04, V-412 and French 05-01. The results showed that all of the RHDV and RHDVa strains cause an increase in the number of apoptotic cells throughout the infection, which might indicate the need for further analysis of the importance of this process.

Apoptosis of peripheral blood leucocytes in rabbits infected with different strains of rabbit haemorrhagic disease virus

The pathogenicity of RHDV (rabbit haemorrhagic disease virus) is mainly associated with its affinity to blood vessels, with causing disseminated intravascular coagulations (DIC), and with the stimulation of the host immune system. Moreover, there are implications suggesting that apoptosis may be a pivotal process in understanding the basis of viral haemorrhagic disease in rabbits - a serious infectious disease causing mortality to wild and domestic rabbits. The aim of this study is to evaluate, by means of flow cytometry, the dynamics of apoptosis in peripheral blood granulocytes and lymphocytes in rabbits experimentally infected with seven different strains of RHDV and so-called antigenic variants of RHDV denominated as RHDVa, i.e.: Hungarian 24V/89, 1447V/96, 72V/2003; Austrian 01-04, 237/04, V-412 and French 05-01. The results showed that all of the RHDV and RHDVa strains cause an increase in the number of apoptotic cells throughout the infection, which might indicate the need for further analysis of the importance of this process.

Analysis of genetic variability and phylogenetic analysis of selected Czech and French strains of rabbit haemorrhagic disease virus (RHDV)

The objective of this study was to analyse the genetic variability and phylogenetic analysis of six strains of rabbit haemorrhagic disease virus (RHDV), including four Czech strains (CAMPV-351, CAMPV-561, CAMPV-562, CAMPV-558) and two French strains (Fr-1, Fr-2), on the basis of a fragment of the VP60 capsid structural protein-coding gene N-terminal region. The results of our own studies were compared to 26 RHDV strains obtained from GenBank. The analysis of the genetic variability of six RHDV strains indicated that the CAMPV-561 strain is the most genetically variable. Less variable were the Fr-1 and Fr-2 strains, while the least variable was CAMPV-351. In turn, the genetic distance among the six analysed strains and 26 strains obtained from GenBank was the greatest for CAMPV-351 and Whn/China [11.3 % according to the observed divergence (OD) method and 12.2 % according to the maximum likelihood (ML) method], while it was the lowest for CAMPV-351 and FRG (0.8 % in both the OD and ML methods). In turn, the scale of the genetic distances among the six analysed strains and five RHDVa strains (99-05, NY-01, Whn/China, Triptis, Iowa2000) ranged from 9.3–10.3 % in the OD method to 10.3–13.7 % in the ML method. The image of phylogenetic dependencies generated for the strains analysed and those obtained from GenBank revealed their distribution to be in five genetic groups (G1–G5), whereas the analysed strains were included in genetic groups 2 and 3.

Genetic variation and phylogenetic analysis of rabbit haemorrhagic disease virus (RHDV) strains

Rabbit haemorrhagic disease virus (RHDV) belongs to the family Caliciviridae and is the etiological agent of the haemorrhagic disease, also known as rabbit plague. Its genome is a linear single-stranded (ss) RNA of 7437 nucleotides and the capsid is built from a single structural protein VP60. In connection with the discovery of new RHDV strains, there is a constant need to investigate the genetic variation of this virus and perform phylogenetic analyses which may show the evolutionary relationships among the RHDV strains. Studies on the divergence of RHDV have shown that it is genetically quite stable, although recent observations indicate that some new RHDV strains, significantly different from the original RHDV subtype and the new RHDVa subtype, are appearing. These latest findings suggest that a new group of RHDV strains has evolved. The present review summarizes the current knowledge on the genetic variation and the latest achievements in phylogenetic analyses of RHDV strains isolated in various countries.

Genetic variation and phylogenetic analysis of rabbit haemorrhagic disease virus (RHDV) strains

Rabbit haemorrhagic disease virus (RHDV) belongs to the family Caliciviridae and is the etiological agent of the haemorrhagic disease, also known as rabbit plague. Its genome is a linear single-stranded (ss) RNA of 7437 nucleotides and the capsid is built from a single structural protein VP60. In connection with the discovery of new RHDV strains, there is a constant need to investigate the genetic variation of this virus and perform phylogenetic analyses which may show the evolutionary relationships among the RHDV strains. Studies on the divergence of RHDV have shown that it is genetically quite stable, although recent observations indicate that some new RHDV strains, significantly different from the original RHDV subtype and the new RHDVa subtype, are appearing. These latest findings suggest that a new group of RHDV strains has evolved. The present review summarizes the current knowledge on the genetic variation and the latest achievements in phylogenetic analyses of RHDV strains isolated in various countries.

Genetic variability of Czech and German RHD virus strains

RHD (rabbit haemorrhagic disease) virus (RHDV) is the aetiological factor of the haemorrhagic disease of rabbits and is currently present on all continents. RHDV is a small, envelope-free virus containing genetic material in the form of a 7437-nucleotide long RNA strand. Studies indicate that genetic variability of RDHV strains originating from various parts of the world is approximately 14%, regardless the time and place of isolation. The aim of this study was to evaluate the genetic variability of 6 RHD virus strains from the Czech Republic (CAMPV-561, CAMPV-562, CAMPV-558) and Germany (Frankfurt, Wika, Rossi) based on analysis of fragment of a gene coding a nonstructural p30 protein. The largest variability of nucleotide sequences within the studied fragment was found for the Rossi strain and CAMPV-562 (13.5%) and CAMPV-558 (13.5%), Wika and Frankfurt (12.1%), and CAMPV-561 and Wika (11.2%). Among the Czech strains the largest genetic distance was noted for strains CAMPV-558 and Iowa (0.130/0.140), and in the case of the German strains, for Frankfurt and Iowa (0.123/0.132). A homology tree constructed based on a fragment of a p30 protein-coding gene divided the 14 analysed strains into IV groups of 88% homology. Phylogenetic relationships also divided the tested strains into 4 genetic groups (G1-G4). The larger genetic distance exists between the Czech and German strains and the American ones, and the smallest between them and the European strains.