Are all lyssavirus genes equal for phylogenetic analyses?

Evaluation of Taxonomic Characteristics of Matlo and Phala Bat Rabies-Related Lyssaviruses Identified in South Africa

We report the genetic characterization of two potentially novel rabies-related lyssaviruses identified from bats in Limpopo province, South Africa. Matlo bat lyssavirus (MBLV) was identified in two Miniopterus natalensis (Natal long-fingered) bats in 2015 and 2016, and Phala bat lyssavirus (PBLV) was identified in a Nycticeinops schlieffeni (Schlieffen's) bat in 2021. The distribution of both of these bat species is largely confined to parts of Africa, with limited reports from the Arabian Peninsula. MBLV and PBLV were demonstrated to group with the unassigned and phylogroup I lyssaviruses, respectively. MBLV was most closely related to Lyssavirus caucasicus (WCBV), whereas PBLV was most closely related to Lyssavirus formosa (TWBLV-1) and Taiwan bat lyssavirus 2 (TWBLV-2), based on analysis of the N and G genes, the concatenated N + P + M + G + L coding sequence, and the complete genome sequence. Based on our analysis, MBLV and WCBV appeared to constitute a phylogroup separate from Lyssavirus lleida (LLEBV) and Lyssavirus ikoma (IKOV). Analysis of the antigenic sites suggests that PBLV will likely be serologically distinguishable from established lyssaviruses in virus-neutralization tests, whereas MBLV appeared to be antigenically highly similar to WCBV. Taken together, the findings suggested that, while PBLV is likely a new lyssavirus species, MBLV is likely related to WCBV.

Rabies Infection: An Overview of Lyssavirus-Host Protein Interactions

Viruses are obligatory intracellular parasites that use cell proteins to take the control of the cell functions in order to accomplish their life cycle. Studying the viral-host interactions would increase our knowledge of the viral biology and mechanisms of pathogenesis. Studies on pathogenesis mechanisms of lyssaviruses, which are the causative agents of rabies, have revealed some important host protein partners for viral proteins, especially for most studied species, i.e. RABV. In this review article, the key physical lyssavirus-host protein interactions, their contributions to rabies infection, and their exploitation are discussed to improve the knowledge about rabies pathogenesis.

Phylogenetic analysis of near full-length sequences of the Desmodus rotundus genetic lineage of rabies virus

The World Health Organization (WHO), reports that rabies causes tens of thousands of deaths every year killing humans, non-human primates and other animals. Rabies continues to be a public health issue, despite the existence of effective vaccines. The dogs remain the primary reservoir and transmitter of rabies to humans globally. In the Americas, bats are regarded as the second most common source of rabies virus to humans. The vampire bat Desmodus rotundus has been identified as a natural reservoir of rabies virus (RABV) in this region. The complete genome of the RABV variant maintained by populations of vampire bats D. rotundus has rarely been reported. In this study, we sequenced and analyzed the genome of a RABV variant detected in D. rotundus. The sample, collected from an endemic area in São Paulo State, was phylogenetically compared with the genome of the standard sample for species Rabies virus as well as other samples belonging to terrestrial and bat-associated cycles of rabies transmission, available in GenBank. Distinct patterns linked to the genetic lineage were identified. These data can aid in the understanding of the molecular epidemiology of this virus and the epidemiological importance of this species in the transmission of the RABV.

Evolutionary analysis of rabies virus isolates from Guangxi Province of southern China

Background

Rabies is a severe epidemic in Guangxi province, China, with hundreds of deaths occurring each year. In the past six decades, rabies has emerged three times in Guangxi, and the province has reported the largest number of rabies cases in China. The domestic dog is the principal vector for rabies, and 95% of human cases are associated with transmission from dogs.

Results

To understand the genetic relationship between street rabies virus (RABV) from Guangxi, genetic diversity analysis was performed using RABV isolates collected between 1999 and 2012. The N gene of 42 RABV isolates, and the P and M genes, as well as fragments of the 3′ terminus (L^1–680) and the polymerase activity module of the L gene (L^pam) of 36 RABV isolates were sequenced. In addition, whole genome sequencing was performed for 5 RABV isolates. There was evidence of topological discrepancy in the phylogenetic trees based on different genes of the RABV isolates. Amino acid variation of the deduced N protein exhibited different patterns to those obtained from the P and M proteins reported here, and the previously reported G protein (Tang H. et al., PLoS Negl Trop Dis, 8(10): e3114, 2014), and L^1–680 and L^pam. These RABV isolates were divided into three main branches against fixed strains.

Conclusion

RABV is prevalent in Guangxi province and strains collected over the last two decades belong mainly to three groups (I, II, III). These RABV isolates reveal genetic diversity. Individual RABV genes from Guangxi exhibit different evolutionary characteristics. The results will have benefits for continuing comprehensive rabies surveillance, prevention and control in China.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1514-0) contains supplementary material, which is available to authorized users.

Defining objective clusters for rabies virus sequences using affinity propagation clustering

Rabies is caused by lyssaviruses, and is one of the oldest known zoonoses. In recent years, more than 21,000 nucleotide sequences of rabies viruses (RABV), from the prototype species rabies lyssavirus, have been deposited in public databases. Subsequent phylogenetic analyses in combination with metadata suggest geographic distributions of RABV. However, these analyses somewhat experience technical difficulties in defining verifiable criteria for cluster allocations in phylogenetic trees inviting for a more rational approach. Therefore, we applied a relatively new mathematical clustering algorythm named ‘affinity propagation clustering’ (AP) to propose a standardized sub-species classification utilizing full-genome RABV sequences. Because AP has the advantage that it is computationally fast and works for any meaningful measure of similarity between data samples, it has previously been applied successfully in bioinformatics, for analysis of microarray and gene expression data, however, cluster analysis of sequences is still in its infancy. Existing (516) and original (46) full genome RABV sequences were used to demonstrate the application of AP for RABV clustering. On a global scale, AP proposed four clusters, i.e. New World cluster, Arctic/Arctic-like, Cosmopolitan, and Asian as previously assigned by phylogenetic studies. By combining AP with established phylogenetic analyses, it is possible to resolve phylogenetic relationships between verifiably determined clusters and sequences. This workflow will be useful in confirming cluster distributions in a uniform transparent manner, not only for RABV, but also for other comparative sequence analyses.

Rabies is one of the oldest known zoonoses, caused by lyssaviruses. In recent years, more than 21,000 nucleotide sequences for rabies viruses (RABV) have been deposited in public databases. In this study, a novel mathematical approach called affinity propagation (AP) clustering, a highly powerful tool, to verifiably divide full genome RABV sequences into genetic clusters, was used. A panel of existing and novel RABV full genome sequences was used to demonstrate the application of AP for RABV clustering. Using a combination of AP with established phylogenetic analyses is useful in resolving phylogenetic relationships between more objectively determined clusters and sequences. This workflow will help to substantiate a transparent cluster distribution, not only for RABV, but also for other comparative sequence analyses.

Spatio-temporal Analysis of the Genetic Diversity of Arctic Rabies Viruses and Their Reservoir Hosts in Greenland

There has been limited knowledge on spatio-temporal epidemiology of zoonotic arctic fox rabies among countries bordering the Arctic, in particular Greenland. Previous molecular epidemiological studies have suggested the occurrence of one particular arctic rabies virus (RABV) lineage (arctic-3), but have been limited by a low number of available samples preventing in-depth high resolution phylogenetic analysis of RABVs at that time. However, an improved knowledge of the evolution, at a molecular level, of the circulating RABVs and a better understanding of the historical perspective of the disease in Greenland is necessary for better direct control measures on the island. These issues have been addressed by investigating the spatio-temporal genetic diversity of arctic RABVs and their reservoir host, the arctic fox, in Greenland using both full and partial genome sequences. Using a unique set of 79 arctic RABV full genome sequences from Greenland, Canada, USA (Alaska) and Russia obtained between 1977 and 2014, a description of the historic context in relation to the genetic diversity of currently circulating RABV in Greenland and neighboring Canadian Northern territories has been provided. The phylogenetic analysis confirmed delineation into four major arctic RABV lineages (arctic 1–4) with viruses from Greenland exclusively grouping into the circumpolar arctic-3 lineage. High resolution analysis enabled distinction of seven geographically distinct subclades (3.I – 3.VII) with two subclades containing viruses from both Greenland and Canada. By combining analysis of full length RABV genome sequences and host derived sequences encoding mitochondrial proteins obtained simultaneously from brain tissues of 49 arctic foxes, the interaction of viruses and their hosts was explored in detail. Such an approach can serve as a blueprint for analysis of infectious disease dynamics and virus-host interdependencies. The results showed a fine-scale spatial population structure in Greenland arctic foxes based on mitochondrial sequences, but provided no evidence for independent isolated evolutionary development of RABV in different arctic fox lineages. These data are invaluable to support future initiatives for arctic fox rabies control and elimination in Greenland.

Next to dog-mediated rabies, wildlife rabies continues to pose a public health problem, particularly in the northern hemisphere. Control of this zoonosis at the animal source has been proven the most efficient route to reduction of human rabies burden. Successful elimination of red fox-mediated rabies in Western Europe and parts of North America has demonstrated the viability of wildlife rabies control strategies. In some regions, the epidemiology of wildlife rabies is well understood; this is not the case for arctic rabies, particularly in Greenland. Previous molecular epidemiological studies demonstrated the occurrence of one particular arctic rabies virus (RABV) lineage (arctic-3) but were limited by low sample numbers and limited sequence length so as to preclude generation of high resolution phylogenetic analysis. Here, a unique set comprised of 79 complete genome sequences of RABVs from Greenland, Canada, USA (Alaska) and Russia collected over the past four decades was analysed. The use of next generation sequencing (NGS) allowed simultaneous determination of host derived sequences encoding mitochondrial proteins from the same brain tissue of 49 arctic foxes. These sequence data combined with geographical and temporal information permit the study of the genetic diversity and evolution of circulating RABVs in Greenland against the background of reservoir host genetics. The results reveal the existence of a single arctic RABV lineage (arctic-3) in Greenland, which has evolved into multiple distinct variants. These analyses provide an improved knowledge of the evolution of the circulating viruses at the molecular level and a better understanding of the historical perspective of the disease in Greenland compared to other parts of the Arctic. This knowledge will support policy on rabies control in mammalian wildlife reservoirs.

Molecular epidemiology of reemergent rabies in Yunnan Province, southwestern China

This province is a focal point for spread of rabies between Southeast Asia and China.

Yunnan Province in China borders 3 countries (Vietnam, Laos, and Myanmar) in Southeast Asia. In the 1980s, a large-scale rabies epidemic occurred in this province, which subsided by the late 1990s. However, 3 human cases of rabies in 2000 indicated reemergence of the disease in 1 county. In 2012, rabies was detected in 77 counties; 663 persons died of rabies during this new epidemic. Fifty two rabies virus strains obtained during 2008–2012 were identified and analyzed phylogenetically by sequencing the nucleoprotein gene. Of the 4 clades identified, clades YN-A and YN-C were closely related to strains from neighboring provinces, and clade YN-B was closely related to strains from Southeast Asia, but formed a distinct branch. Rabies virus diversity might be attributed to dog movements among counties, provinces, and neighboring countries. These findings suggest that Yunnan Province is a focal point for spread of rabies between Southeast Asia and China.

Complex epidemiology of a zoonotic disease in a culturally diverse region: phylogeography of rabies virus in the Middle East

The Middle East is a culturally and politically diverse region at the gateway between Europe, Africa and Asia. Spatial dynamics of the fatal zoonotic disease rabies among countries of the Middle East and surrounding regions is poorly understood. An improved understanding of virus distribution is necessary to direct control methods. Previous studies have suggested regular trans-boundary movement, but have been unable to infer direction. Here we address these issues, by investigating the evolution of 183 rabies virus isolates collected from over 20 countries between 1972 and 2014. We have undertaken a discrete phylogeographic analysis on a subset of 139 samples to infer where and when movements of rabies have occurred. We provide evidence for four genetically distinct clades with separate origins currently circulating in the Middle East and surrounding countries. Introductions of these viruses have been followed by regular and multidirectional trans-boundary movements in some parts of the region, but relative isolation in others. There is evidence for minimal regular incursion of rabies from Central and Eastern Asia. These data support current initiatives for regional collaboration that are essential for rabies elimination.

Phylogeographic dispersion and diversification of rabies virus lineages associated with dogs and crab-eating foxes (Cerdocyon thous) in Brazil

Genetic lineages of dog-associated RABV still circulate in some areas of the North and Northeast of Brazil. In parallel, another RABV lineage circulates among wild canids in the Northeast, particularly the crab-eating fox (Cerdocyon thous). Although previous studies and phylogenetic analyses have been carried out, the way in which these lineages are dispersed temporally and spatially remained to be elucidated. In this study, RABV N gene sequences isolated from canids in North and Northeast Brazil were analyzed by the Bayesian Markov Chain Monte Carlo Method, and the results were then used in a phylogeographic study. It was inferred from the findings that the most recent common ancestor became established at the end of the nineteenth century on the border of the Brazilian states of Paraíba and Pernambuco and diversified into the lineages associated with dogs and C. thous. Around 1910, the original C. thous lineage diversified into two main sublineages in the same area, one of which migrated to the south and the other to the north. The dog-associated lineage diversified around 1945 and moved toward the north and south. From the phylogeographic analysis it was possible to infer not only the movement of the virus lineages but also the probable location where dispersion and diversification occurred. The methodology used here enabled the phylogeographic history of RABV in the region to be reconstructed, and the dispersion pattern of the virus can be used to predict its movements, making it easier to stop the advance of a rabies epidemic.

Genetic diversity and molecular evolution of the rabies virus matrix protein gene in China

To investigate the diversity of rabies virus (RABV) matrix protein (M) gene in the current Chinese rabies epidemic, we fully examined M gene of 63 street RABVs (Virus isolated from naturally infected animals), and performed phylogenetic and mutational analysis. Our results indicate that the Chinese RABV M gene is well conserved with 90.6% to 100% amino acid similarity. Analysis of the mutations indicates that the sequences can be divided into four groups with each group defined by distinct substitutions. The PPxY motif and residue E58, which are essential for efficient virus production and pathogenicity, were completely conserved. The estimated mean rate of nucleotide substitution was 4.6×10(-4) substitutions per site per year, and the estimated average time of the most recent common ancestor (TMRCA) was 265 years ago based on the M gene of Chinese street RABVs, which are similar to previously reported values for the glycoprotein (G) and nucleoprotein (N) gene. This indicates that the genomic RNA of RABVs circulating worldwide is stable; G, N and M genes are evolving at a similar rate. This study showed that although the Chinese RABV strains could be divided into distinct clades based on the phylogenetic analysis, their functional domains of M proteins were highly conserved.

Molecular characterization of KGH, the first human isolate of rabies virus in Korea

The complete genome sequence of the KGH strain of the first human rabies virus, which was isolated from a skin biopsy of a patient with rabies, whose symptoms developed due to bites from a raccoon dog in 2001. The size of the KGH strain genome was determined to be 11,928 nucleotides (nt) with a leader sequence of 58 nt, nucleoprotein gene of 1,353 nt, phosphoprotein gene of 894 nt, matrix protein gene of 609 nt, glycoprotein gene of 1,575 nt, RNA-dependent RNA polymerase gene of 6,384 nt, and trailer region of 69 nt. Sequence similarity was compared with 39 fully sequenced rabies virus genomes currently available, and the result showed 70.6-91.6 % at the nucleotide level, and 82.8-97.9 % at the amino acid level. The deduced amino acids in the viral protein were compared with those of other rabies viruses, and various functional regions were investigated. As a result, we found that the KGH strain only had a unique amino acid substitution that was identified to be associated either with host immune response and pathogenicity in the N protein, or with a related region regulating STAT1 in the P protein, and related to pathogenicity in G protein. Based on phylogenetic analyses using the complete genome of 39 rabies viruses, the KGH strain was determined to be closely related with the NNV-RAB-H strain and transplant rabies virus serotype 1, which are Indian isolates, and was confirmed to belong to the Arctic-like 2 clade. The KGH strain was most closely related to the SKRRD0204HC and SKRRD0205HC strain when compared with Korean animal isolates, which was separated around the same time and place, and belonged to the Gangwon III subgroup.

Phylogenetic analysis of partial RNA-polymerase blocks II and III of Rabies virus isolated from the main rabies reservoirs in Brazil

This study describes the results of the sequencing and analysis of segments of Blocks II and III of the RNA polymerase L gene of Rabies virus isolates from different reservoir species of Brazil. The phylogenetic relations of the virus were determined and a variety of species-specific nucleotides were found in the analyzed areas, but the majority of these mutations were found to be synonymous. However, an analysis of the putative amino acid sequences were shown to have some characteristic mutations between some reservoir species of Brazil, indicating that there was positive selection in the RNA polymerase L gene of Rabies virus. On comparing the putative viral sequences obtained from the Brazilian isolates and other Lyssavirus, it was determined that amino acid mutations occurred in low-restriction areas. This study of the L gene of Rabies virus is the first to be conducted with samples of virus isolates from Brazil, and the results obtained will help in the determination of the phylogenetic relations of the virus.

The 3' untranslated region of the rabies virus glycoprotein mRNA specifically interacts with cellular PCBP2 protein and promotes transcript stability

Viral polymerase entry and pausing at intergenic junctions is predicted to lead to a defined polarity in the levels of rhabdovirus gene expression. Interestingly, we observed that the rabies virus glycoprotein mRNA is differentially over-expressed based on this model relative to other transcripts during infection of 293T cells. During infection, the rabies virus glycoprotein mRNA also selectively interacts with the cellular poly(rC)-binding protein 2 (PCBP2), a factor known to influence mRNA stability. Reporter assays performed both in electroporated cells and in a cell-free RNA decay system indicate that the conserved portion of the 3' UTR of the rabies virus glycoprotein mRNA contains an RNA stability element. PCBP2 specifically interacts with reporter transcripts containing this 72 base 3' UTR sequence. Furthermore, the PCBP2 interaction is directly associated with the stability of reporter transcripts. Therefore, we conclude that PCBP2 specifically and selectively interacts with the rabies virus glycoprotein mRNA and that this interaction may contribute to the post-transcriptional regulation of glycoprotein expression.

From brain passage to cell adaptation: the road of human rabies vaccine development

A major challenge for global rabies prevention and control is the lack of sufficient and affordable high quality vaccines. Such candidates should be pure, potent, safe, effective and economical to produce, with broad cross-reactivity against viral variants of public health and veterinary importance. The history of licensed human vaccines reviewed herein demonstrates clearly how the field has evolved to the current state of more passive development and postexposure management. Modern cell culture techniques provide adequate viral substrates for production of representative verified virus seeds. In contrast to outdated nervous tissue-based rabies vaccines, once a suitable substrate is identified, production of high titer virus results in a major qualitative and quantitative difference. Given the current scenario of only inactivated vaccines for humans, highly cell-adapted and stable, attenuated rabies viruses are ideal candidates for consideration to meet the need for seed viruses in the future.

Differentiation of the seven major lyssavirus species by oligonucleotide microarray

An oligonucleotide microarray, LyssaChip, has been developed and verified as a highly specific diagnostic tool for differentiation of the 7 major lyssavirus species. As with conventional typing microarray methods, the LyssaChip relies on sequence differences in the 371-nucleotide region coding for the nucleoprotein. This region was amplified using nested reverse transcription-PCR primers that bind to the 7 major lyssaviruses. The LyssaChip includes 57 pairs of species typing and corresponding control oligonucleotide probes (oligoprobes) immobilized on glass slides, and it can analyze 12 samples on a single slide within 8 h. Analysis of 111 clinical brain specimens (65 from animals with suspected rabies submitted to the laboratory and 46 of butchered dog brain tissues collected from restaurants) showed that the chip method was 100% sensitive and highly consistent with the "gold standard," a fluorescent antibody test (FAT). The chip method could detect rabies virus in highly decayed brain tissues, whereas the FAT did not, and therefore the chip test may be more applicable to highly decayed brain tissues than the FAT. LyssaChip may provide a convenient and inexpensive alternative for diagnosis and differentiation of rabies and rabies-related diseases.

Molecular phylogenetics of the lyssaviruses--insights from a coalescent approach

Technical improvements over the past 2 decades have enormously facilitated the generation of nucleotide sequence data for lyssavirus collections. These databases are amenable to methods of phylogenetic analysis, which attempt to define the taxonomic structure of this genus and predict the evolutionary relationships of current circulating strains. Coupled with a range of mathematical tools to explore the appropriateness of nucleotide substitution models and test for positive selection, the evolutionary process is being explored in detail. Despite the potential for high viral mutation levels, the operation of purifying selection appears to effectively constrain lyssavirus evolution. The recent development of coalescent theory has provided additional approaches to data analysis whereby the time frame of emergence of viral lineages can be most reliably estimated. Such studies suggest that all currently circulating rabies viruses have emerged within the past 1500 years. Moreover, through the capability of analyzing viral population dynamics and determining patterns of population size variation, coalescent approaches can provide insight into the demographics of viral outbreaks. Whereas human-assisted movement of reservoir host species has clearly facilitated transfer of rabies between continents, topographical landscape features significantly influence the rate and extent of contiguous disease spread. Together with empirical studies on virus diversity, the application of coalescent approaches will help to better understand lyssavirus emergence, evolution, and spread. In particular, such methods are presently facilitating exploration of the factors operating to limit the ability of lyssaviruses to establish new persistent virus-host associations and ultimately control the emergence of new species of this genus.

Diagnosis and molecular characterization of rabies virus from a buffalo in China: a case report

Background

Rabies virus (RABV) can infect many different species of warm-blooded animals. Glycoprotein G plays a key role in viral pathogenicity and neurotropism, and includes antigenic domains that are responsible for membrane fusion and host cell receptor recognition.

Case presentation

A case of buffalo rabies in China was diagnosed by direct fluorescent antibody test, G gene reverse-transcriptase polymerase chain reaction, and RABV mouse inoculation test. Molecular characterization of the RABV was performed using DNA sequencing, phylogenetic analysis and amino acid sequence comparison based on the G gene from different species of animals.

Conclusion

The results confirmed that the buffalo with suspected rabies was infected by RABV, which was genetically closely related to HNC (FJ602451) that was isolated from cattle in China in 2007. Comparison of the G gene among different species of animal showed that there were almost no amino acid changes among RABVs isolated from the same species of animals that distributed in a near region. However, there were many changes among RABVs that were isolated from different species of animal, or the same species from different geographic regions. This is believed to be the first case report of buffalo rabies in China, and the results may provide further information to understand the mechanism by which RABV breaks through the species barrier.

Shimoni bat virus, a new representative of the Lyssavirus genus

During 2009, 616 bats representing at least 22 species were collected from 10 locations throughout Kenya. A new lyssavirus, named Shimoni bat virus (SHIBV), was isolated from the brain of a dead Commerson's leaf-nosed bat (Hipposideros commersoni), found in a cave in the coastal region of Kenya. Genetic distances and phylogenetic reconstructions, implemented for each gene and for the concatenated alignment of all five structural genes (N, P, M, G and L), demonstrated that SHIBV cannot be identified with any of the existing species, but rather should be considered an independent species within phylogroup II of the Lyssavirus genus, most similar to Lagos bat virus (LBV). Antigenic reaction patterns with anti-nucleocapsid monoclonal antibodies corroborated these distinctions. In addition, new data on the diversity of LBV suggests that this species may be subdivided quantitatively into three separate genotypes. However, the identity values alone are not considered sufficient criteria for demarcation of new species within LBV.

Development of combined vaccines for rabies and immunocontraception

Rabies prevention and appropriate population management of free-ranging animals have an important role to play in the eventual elimination of rabies in dogs. An effective sterilant based on rabies vaccines has the potential to create a supportive measure of public acceptability and to reduce associated clinic visit costs. We inserted the coding sequence of gonadotropin-releasing hormone (GnRH) into different locations within the rabies virus ERA glycoprotein (G) gene, and demonstrated that the amino terminus (N), antigenic site IIa, and the junction between the ecto- and cytoplasmic domains (C) of the G were suitable sites for GnRH insertion. The rescued recombinant rabies viruses ERA-N-GnRH and ERA-C-GnRH grew as well as the parental ERA virus, reaching 1x10(9)ffu/ml in cell culture. Insertion and expression of the GnRH were stable in the viruses after multiple passages in vitro. To increase immunogenicity of the GnRH peptide, two copies of GnRH, aligned in tandem, were fused to the N terminus of the G. The recombinant rabies virus ERA-N-2GnRH was recovered and grown to high titers in cell culture. All GnRH-carrying rabies viruses induced antibodies against GnRH in immunized mice and protected 100% of the animals after rabies virus challenge. The recombinant viruses reacted strongly with the serum from a GonaCon-immunized animal. The GnRH-carrying rabies viruses have significant potential in rabies and animal population control.

Relaxation of purifying selection on the SAD lineage of live attenuated oral vaccines for rabies virus

Analysis of patterns of nucleotide sequence diversity in wild-type rabies virus (RABV) genomes and in the SAD live attenuated oral vaccine lineage was used to test for the relaxation of purifying selection in the latter and provide evidence regarding the genomic regions where such relaxation of selection occurs. The wild-type sequences showed evidence of strong past and ongoing purifying selection both on nonsynonymous sites in coding regions and on non-coding regions, particularly the start, end and 5' UTR regions. SAD vaccine sequences showed a relaxation of purifying selection at nonsynonymous sites in coding regions, resulting a substantial number of amino acid sequence polymorphisms at sites that were invariant in the wild-type sequences. Moreover, SAD vaccine sequences showed high levels of mutation accumulation in the non-coding regions that were most conserved in the wild-type sequences. Understanding the biological effects of the unique mutations accumulated in the vaccine lineage is important because of their potential effects on antigenicity and effectiveness of the vaccine.

Molecular characterization of Rabies Virus isolates from dogs and crab-eating foxes in Northeastern Brazil

Thirty-eight samples of Rabies Virus isolated from dogs and crab-eating foxes (Cerdocyon thous) in Northeastern Brazil were characterized genetically by analyzing the G gene and the psi region. The results show that there are two groups of Rabies Virus lineages circulating among domestic and wild animals in the region. The topologies of the phylogenetic trees of the G gene and psi region are similar and reveal the existence of geographic groups. The genetic diversity of the lineages isolated from wild animals (wild group) was approximately twice that of the lineages isolated from domestic animals (domestic group), and the genetic distance between the two groups was 9.93%. Polymorphism analysis revealed specific intra- and inter-group molecular signatures for both the G gene and psi region. Together with the analysis of the N gene undertaken previously, the results of this study confirm the existence of a Rabies Virus phylogroup in Northeastern Brazil (NB) circulating in the C. thous population, making this species a rabies biotype in the region.

Characterization of human rabies virus vaccine strain in China

Human rabies virus vaccine strain CTN181 from China was sequenced. The overall length of the genome was 11,923 nucleotides (nt), comprising a leader sequence of 58 nt, nucleoprotein (N) gene of 1353 nt, phosphoprotein (P) gene of 894 nt, matrix protein (M) gene of 609 nt, glycoprotein (G) gene of 1575 nt, RNA-dependent RNA polymerase (RdRp, L) gene of 6387 nt, and a trailer region of 70 nt. The five monocistrons are separated by intergenic regions (IGRs) of 2, 5, 5 and 24 nucleotides (nt), respectively. Two obvious differences between CTN181 and the other rabies virus vaccine strains were (1) the putative stop/polyadenylation signal of the G gene has only one poly (A) tract for CTN181, and (2) the start of the open reading frame for L has two repeats of ATG for CTN181. Both were similar to the SHBRV-18 (silver-haired bat-associated RV strain 18) strain. In addition, some mutations and new functional regions were discovered that are presumed crucial to the function of leader region and L protein. There is an equal role for all five genes in the phylogenetics of rabies virus.

Genomic diversity and evolution of the lyssaviruses

Lyssaviruses are RNA viruses with single-strand, negative-sense genomes responsible for rabies-like diseases in mammals. To date, genomic and evolutionary studies have most often utilized partial genome sequences, particularly of the nucleoprotein and glycoprotein genes, with little consideration of genome-scale evolution. Herein, we report the first genomic and evolutionary analysis using complete genome sequences of all recognised lyssavirus genotypes, including 14 new complete genomes of field isolates from 6 genotypes and one genotype that is completely sequenced for the first time. In doing so we significantly increase the extent of genome sequence data available for these important viruses. Our analysis of these genome sequence data reveals that all lyssaviruses have the same genomic organization. A phylogenetic analysis reveals strong geographical structuring, with the greatest genetic diversity in Africa, and an independent origin for the two known genotypes that infect European bats. We also suggest that multiple genotypes may exist within the diversity of viruses currently classified as 'Lagos Bat'. In sum, we show that rigorous phylogenetic techniques based on full length genome sequence provide the best discriminatory power for genotype classification within the lyssaviruses.

Genetic characterisation of attenuated SAD rabies virus strains used for oral vaccination of wildlife

The elimination of rabies from the red fox (Vulpes vulpes) in Western Europe has been achieved by the oral rabies vaccination (ORV) of wildlife with a range of attenuated rabies virus strains. With the exception of the vaccinia rabies glycoprotein recombinant vaccine (VRG), all strains were originally derived from a common ancestor; the Street Alabama Dufferin (SAD) field strain. However, after more than 30 years of ORV it is still not possible to distinguish these vaccine strains and there is little information on the genetic basis for their attenuation. We therefore sequenced and compared the full-length genome of five commercially available SAD vaccine viruses (SAD B19, SAD P5/88, SAG2, SAD VA1 and SAD Bern) and four other SAD strains (the original SAD Bern, SAD VA1, ERA and SAD 1-3670 Wistar). Nucleotide sequencing allowed identifying each vaccine strain unambiguously. Phylogenetic analysis revealed that the majority of the currently used commercial attenuated rabies virus vaccines appear to be derived from SAD B19 rather than from SAD Bern. One commercially available vaccine virus did not contain the SAD strain mentioned in the product information of the producer. Two SAD vaccine strains appeared to consist of mixed genomic sequences. Furthermore, in-del events targeting A-rich sequences (in positive strand) within the 3' non-coding regions of M and G genes were observed in SAD-derivates developed in Europe. Our data also supports the idea of a possible recombination that had occurred during the derivation of the European branch of SAD viruses. If confirmed, this recombination event would be the first one reported among RABV vaccine strains.

Glycoprotein gene relocation in rabies virus

Unlike vesicular stomatitis virus, rabies virus glycoprotein gene has not been successfully relocated closer to promoter-proximal regions by reverse genetics. Here we describe an efficient system for the Evelyn-Rokitnicki-Abelseth (ERA) rabies virus with the glycoprotein gene switched with the matrix protein gene, creating a reshuffled virus ERAgm (gene order N-P-G-M-L). With the aid of an autogene plasmid, the T7 RNA polymerase containing a nuclear location signal from the SV40 large T antigen facilitated virus recovery. The rearranged ERAgm rabies virus replicated as well as the parental ERA (gene order N-P-M-G-L) virus, reaching 10(9) ffu/ml in infected BSR cells. The altered glycoprotein gene position in viral genome presented an alternative way to study the pathogenicity of rabies virus. This also provides a potential novel method for rabies vaccine development.

Lyssaviruses: current trends

Various technological developments have revitalized the approaches employed to study the disease of rabies. In particular, reverse genetics has facilitated the generation of novel viruses used to improve our understanding of the fundamental aspects of rabies virus (RABV) biology and pathogenicity and yielded novel constructs potentially useful as vaccines against rabies and other diseases. Other techniques such as high throughput methods to examine the impact of rabies virus infection on host cell gene expression and two hybrid systems to explore detailed protein-protein interactions also contribute substantially to our understanding of virus-host interactions. This review summarizes much of the increased knowledge about rabies that has resulted from such studies but acknowledges that this is still insufficient to allow rational attempts at curing those who present with clinical disease.