Jemma Smith

Phylogenetic comparison of the genus Lyssavirus using distal coding sequences of the glycoprotein and nucleoprotein genes

Summary. The phylogenetic relationships between all seven genotypes within the genus Lyssavirus were compared at the nucleotide level utilising two distal regions of the viral genome. The resulting analysis of each region produced similar, although not identical, phylogenetic results, suggesting that the evolutionary pressures on individual proteins within the genome vary. These differences are in part due to the increased variability observed within the glycoprotein sequence over the nucleoprotein sequence. Pair-wise comparison using the glycoprotein partial sequence between different isolates demonstrate that within genotypes, viruses show between 80 and 100% sequence identity, whilst between genotypes, viruses show between 50 and 75% identity. This provides a consistent guide to assigning new viruses to existing genotypes. Alignment of the amino acid sequence for the truncated glycoprotein sequence to the Pasteur Virus vaccine strain show significant residue variation between positions 139 and 170. However, residue variation tends to vary with genotype implying that these changes have not evolved due to immunological pressure from the host but have occurred following the separation of viruses into discrete groups. Comparison of the phylogenetic analysis for this partial region of the glycoprotein suggest that it gives comparable results to studies that have used larger regions of the Lyssavirus genome.

Rabies emergence among foxes in Turkey.

Sixteen rabies isolates recently collected from mainland Turkey and two isolates held within a British archive were used to form a representative cohort from a range of vectors, and were analyzed to identify potential causes for an increase of rabies within the fox (Vulpes vulpes) population in Turkey. Each isolate was characterized by sequence analysis of the nucleoprotein gene and compared phylogenetically to the cohort, to isolates from neighboring countries and to isolates from continental Europe and Russia. From this analysis the isolates could be divided into three groups associated with geographic location. This included a western group, an eastern group, and one isolate that did not group with any other Turkish isolate. This observation was also found using the heteroduplex mobility assay as an alternative method for typing rabies virus isolates. Further comparison with isolates from neighboring countries suggests that this isolate was related to viruses present in Georgia and could represent a recent import to Turkey from that country. Within the two larger groups, sequence data were obtained from both infected dogs and foxes suggesting that there has been transmission of virus between these two species. The direction of transmission could not be identified by the phylogenetic analysis, although absence of rabies within the fox population in previous years suggests that this could represent a recent spillover from the domestic dog to the fox.

A rapid RT-PCR method to differentiate six established genotypes of rabies and rabies-related viruses using TaqMan™ technology

Abstract A rapid and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay incorporating TaqMan™ probes has been developed that can distinguish among the six established rabies and rabies-related virus genotypes. TaqMan™ probes were designed and validated against 106 rabies and rabies-related virus isolates, one isolate of the Australian bat Lyssaviruses (genotype 7), and 18 other non-rabies viruses important in the veterinary field. The N gene was used as the target for the probes as it is well conserved and has been intensively used to genotype rabies isolates. Additionally, it was found to contain regions specific to each genotype conducive to probe design. The RT-PCR assay described amplifies a portion of the nucleoprotein gene of all 107 rabies and rabies-related viruses, but none of the other viruses tested. Inclusion of TaqMan™-genotype-specific probes in the RT-PCR assay permits rapid identification of the virus present. By combining RT-PCR with TaqMan™ genotyping probes suspect rabies virus isolates can be identified in a single closed tube system that prevents potential PCR-product carry over contamination.

Assessment of template quality by the incorporation of an internal control into a RT-PCR for the detection of rabies and rabies-related viruses.

A method is described to assess RNA template quality by the incorporation of a ribosomal RNA (rRNA) internal (in tube) control into a standard rabies and rabies-related virus specific RT-PCR. Specific virus and rRNA templates were co-amplified in a duplex reaction from RNA extracts derived from 60 isolates representing all six of the established lyssavirus genotypes. To ensure a wide species applicability of this technique we demonstrated that the rRNA assay was capable of functioning using the cells or tissues of 14 different mammals. Parallel studies between the duplex and the unlinked lyssavirus assay demonstrated only a minor reduction in the sensitivity of the former test. The ribosomal and viral targets (unlike beta-actin RNA) were shown to have similar degradation kinetics making rRNA amplification a good control for viral target integrity. As a consequence, the use of this system would reduce the likelihood of obtaining false negative RT-PCR results from lyssavirus infected material.

Investigation of a human case of rabies in the United Kingdom

In May of 2001 a Nigerian woman visiting the United Kingdom presented with fever, headache and difficulty swallowing. Within 24 h she showed a marked deterioration and died shortly afterwards. Autopsy samples from a range of tissues were analysed to confirm a clinical diagnosis of rabies. Phylogenetic analysis of the viral nucleoprotein gene confirmed that this was an infection with a genotype 1 virus (classical rabies) belonging to the Africa 2 group, which is endemic in Northern Africa. Comparison of both the nucleoprotein and glycoprotein coding sequences of this isolate with an imported case of human rabies from 1996, also from Nigeria, showed that the two viruses were 99% homologous.

Molecular methods to distinguish between classical rabies and the rabies-related European bat lyssaviruses.

A rapid and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay for the detection of classical rabies virus (genotype 1) and the rabies related European bat lyssaviruses (EBLs) (genotypes 5 and 6) was developed. When combined with specific oligonucleotide probes and a PCR-enzyme linked immunosorbent assay (PCR-ELISA), genotype 5 and 6 viruses can be distinguished from each other and from genotype 1 viruses. Ninety-two isolates from the six established genotypes of rabies and rabies-related viruses were screened by RT-PCR and PCR-ELISA to determine the specificity of the assays. All genotype 1, 5 and 6 viruses were detected by RT-PCR while none of the genotype 2, 3 and 4 viruses were detected. All the genotype 5 and 6 viruses were detected by the two PCR-ELISA probes when used in combination while none of the genotype 1-4 viruses were detected. When used individually, the PCR-ELISA probes also distinguished between the genotype 5 and 6 viruses. This new discriminatory test should allow the rapid genotyping of all lyssaviruses likely to be encountered in Europe and as such could provide useful epidemiological information in the event of an outbreak.

Use of Rapid Cycle Real-Time PCR for the Detection of Rabies Virus

Classical rabies virus (RV) is a member of the Lyssavirus genus within the Rhabdoviridae family, and is a causative agent of rabies. The virus has a wide host range, most probably including all mammals.