A modified rapid enzyme immunoassay for the detection of rabies and rabies-related viruses: RREID-lyssa

Evaluation of Enzyme Linked Immuno-Sorbent Assay and Rapid Immuno-Diagnostic Test for Rabies Antigen Detection in Archived Dog Brain Tissues

Rabies urgently requires strengthening of new and existing diagnostic methodology in order to overcome the threat it poses. We evaluated the Enzyme Linked Immuno-Sorbent Assay (ELISA) and the Rapid Immunodiagnostic Test (RIDT) in detecting rabies viral antigens, comparing both tests with the Direct Fluorescent Antibody Test (DFAT) which is the gold standard in rabies diagnosis. Fifty dog brain tissues collected from the archives of the Central Diagnostic Laboratory, National Veterinary Research Institute, Vom, Nigeria, were utilized for this study. ELISA performed better than RIDT and recorded equivalent result with DFAT as compared with RIDT. There was a 96 % agreement between ELISA and DFAT for rabies antigen detection (concordance coefficient 78 % : 95 % C. I. 0.6366 to 0.8654) while there was a 54 % agreement between RIDT and DFAT (concordance coefficient 17 % : 95 % C. I. 0.05138—0.2752). Compared to DFAT, the sensitivities of ELISA and RIDT were 95.5 % and 47.6 %, respectively, and the specificities of ELISA and RIDT were 100 % and 87.5 % respectively. The simple Cohen’s kappa coefficient for ELISA related to the DFAT was found to be 0.834 (95 % C. I. 0.613—1.0). For RIDT, the Kappa value was 0.170 (95 % C. I. 0.003—0.337). The ELISA is as reliable a diagnostic method as the DFAT which is the gold standard for rabies diagnosis. It has an advantage of being able to analyse large number of samples at the same time, making it more suitable for epidemiological studies and for laboratories that cannot perform the DFAT. The unsatisfactory result of RIDT in this study reiterates the need to perform an adequate test validation before it can be used in the laboratory for rabies diagnosis.

Evaluation of a Rapid Immunochromatographic Diagnostic Test for the detection of rabies from brain material of European mammals

The surveillance of rabies relies on investigations conducted on dead suspected animals or animals showing clinical signs suggestive of rabies. An immunochromatographic method based on lateral flow principle has been evaluated against a collection of brain samples mainly of European mammals including bats. The performance of this new test has been compared to the conventional gold standard methods: the fluorescent Antibody Test (FAT) and the Rapid Tissue Culture Infection Test (RTCIT). This test enabled the detection of various rabies strains belonging to rabies species 1, 5, 6 and 7 and demonstrated an overall specificity of 100% and a sensitivity of more than 88% when compared to FAT and RTCIT. A total agreement between the Rapid Immunochromatographic Diagnostic Test and conventional technique results have been obtained for European bat samples.

A simple sandwich ELISA (WELYSSA) for the detection of lyssavirus nucleocapsid in rabies suspected specimens using mouse monoclonal antibodies

Monoclonal antibody (MAb)-based capture enzyme-linked immunosorbent assays (ELISA) were developed for the diagnosis of rabies-suspect specimens. A combination of four mouse monoclonal antibodies directed against the rabies virus nucleocapsid was selected and used for the detection. The test was optimized and standardized so that maximum concordance could be maintained with the standard procedures of rabies diagnosis recommended by the WHO expert committee. Using prototype viruses from the different genotypes of lyssavirus and from various geographic origins and phylogenetic lineages, this paper presents a reliable, rapid and transferable diagnostic method, named WELYSSA that readily permits the detection of lyssaviruses belonging to the 7 genotypes of lyssavirus circulating in Europe, Africa, Asia and Oceania. The threshold of detection of lyssavirus nucleocapsids is low (0.8 ng/ml). With a panel of 1030 specimens received for rabies diagnostic testing, this test was found to be highly specific (0.999) and sensitive (0.970) when compared to other recommended rabies diagnostic methods.

Molecular diagnosis of lyssaviruses and sequence comparison of Australian bat lyssavirus samples

OBJECTIVE

To evaluate and implement molecular diagnostic tests for the detection of lyssaviruses in Australia.

DESIGN

A published hemi-nested reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of all lyssavirus genotypes was modified to a fully nested RT-PCR format and compared with the original assay. TaqMan assays for the detection of Australian bat lyssavirus (ABLV) were compared with both the nested and hemi-nested RT-PCR assays. The sequences of RT-PCR products were determined to assess sequence variations of the target region (nucleocapsid gene) in samples of ABLV originating from different regions.

RESULTS

The nested RT-PCR assay was highly analytically specific, and at least as analytically sensitive as the hemi-nested assay. The TaqMan assays were highly analytically specific and more analytically sensitive than either RT-PCR assay, with a detection level of approximately 10 genome equivalents per microl. Sequence of the first 544 nucleotides of the nucleocapsid protein coding sequence was obtained from all samples of ABLV received at Australian Animal Health Laboratory during the study period.

CONCLUSION

The nested RT-PCR provided a means for molecular diagnosis of all tested genotypes of lyssavirus including classical rabies virus and Australian bat lyssavirus. The published TaqMan assay proved to be superior to the RT-PCR assays for the detection of ABLV in terms of analytical sensitivity. The TaqMan assay would also be faster and cross contamination is less likely. Nucleotide sequence analyses of samples of ABLV from a wide geographical range in Australia demonstrated the conserved nature of this region of the genome and therefore the suitability of this region for molecular diagnosis.

Clinical laboratory advances in the detection of rabies virus

Rabies is one of the most feared zoonotic diseases in the world. All warm-blooded animals are susceptible to infection by the virus, but the main vectors of human infection are dogs and cats. Development of rabies can be prevented by postexposure vaccination, and with a few exceptions, the exact time and source of human infection is usually known. However, the effective use of postexposure vaccination depends on the rapid and accurate detection of rabies virus in specimens obtained from the source of human infection. This paper provides an overview on developments on laboratory methods for the early detection of rabies virus. In most laboratories, the fluorescent antibody test (FAT) is used as the most important primary test, with the rabies tissue culture infection test (RTCIT) or the mouse inoculation test (MIT) being used as confirmatory backup procedures. However, other methods for the detection of antigens, such as rapid rabies-specific enzyme-linked immunosorbent assay (rapid-ELISA) and the detection of viral nucleic acids by reverse transcription polymerase chain reaction (RT-PCR) are increasingly being used for diagnosis and, in combination with nucleotide sequencing, for epidemiological investigations.

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

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.

Preliminary report on a single-tube, non-interrupted reverse transcription-polymerase chain reaction for the detection of rabies virus in brain tissue

A simple method for the rapid detection of rabies virus was developed employing a single-tube reverse transcription polymerase chain reaction (RT-PCR). The method utilized a single buffer system for both RT and PCR and was performed without interruption as a single thermal cycling programme. Two primer sets within the genes coding for rabies nucleoprotein and glycoprotein were used to amplify a 533 bp and a 406 bp amplicon, respectively. The amplified products were detected with a challenge virus strain (CVS) of rabies. There was no amplified product with uninfected mouse or dog brain. The method was applied to detect rabies virus in 10 mouse inoculation test (MIT)-positive and three MIT-negative brain tissue samples. The amplified product was found only in the MIT-positive samples. The amplified product was confirmed by restriction endonuclease analysis using Hinf1. The results from RT-PCR correlated well with the results from MIT. This indicates that the single-tube RT-PCR may be a useful method for detecting rabies virus in brain tissue samples from suspected cases of rabies.

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.

Detection and identification of rabies and rabies-related viruses using rapid-cycle PCR

The rapid identification of suspect rabies infection is essential in human cases, to ensure appropriate post-exposure treatment of contacts, and in animal cases to allow specific control strategies to be decided and implemented. We describe here the use of high speed air thermo-cycler PCR as a diagnostic tool for the detection of rabies and rabies-related viruses. Using this technique we were able to diagnose rabies in a human within 5 h. Furthermore, the application of automated sequencing of the resultant product enabled a definitive characterisation of classical rabies within 16 h. The utility of this assay was confirmed further by the successful detection of representatives of the six lyssavirus genotypes.

A new quantitative method for rabies virus by detection of nucleoprotein in virion using ELISA

We have developed a new quantitative method for rabies virus (RV) detection using enzyme-linked immunosorbent assay (ELISA). The method named N-ELISA was based on the quantitation of nucleoprotein (N) in RV virions captured by RV-specific polyclonal antibodies on an ELISA plate. Both infective and defective interfering (DI) particles of RV could be detected by this method. When viruses were propagated in a medium of pH 7.4 adjusted with 7% NaHCO3, N-ELISA could detect them with titers of more than 10(6) pfu/ml, though the result did not correlate highly with that of the infectivity assay. The reason for this was considered to be that RVs included spikeless and damaged particles which were produced under conditions of low or high pH. However, in the time course of virus yield, titers of N-ELISA correlated well with those of the infectivity assay.

Heminested PCR assay for detection of six genotypes of rabies and rabies-related viruses

A heminested reverse transcriptase PCR (hnRT-PCR) protocol which is rapid and sensitive for the detection of rabies virus and rabies-related viruses is described. Sixty isolates from six of the seven genotypes of rabies and rabies-related viruses were screened successfully by hnRT-PCR and Southern blot hybridization. Of the 60 isolates, 93% (56 of 60) were positive by external PCR, while all isolates were detected by heminested PCR and Southern blot hybridization. We also report on a comparison of the sensitivity of the standard fluorescent-antibody test (FAT) for rabies antigen and that of hnRT-PCR for rabies viral RNA with degraded tissue infected with a genotype 1 virus. Results indicated that FAT failed to detect viral antigen in brain tissue that was incubated at 37 degrees C for greater than 72 h, while hnRT-PCR detected viral RNA in brain tissue that was incubated at 37 degrees C for 360 h.

Human immunization in developing countries: practical and theoretical problems and prospects

While measles, pertussis and tetanus were responsible during the early 1990s for nearly two million deaths in developing countries, no deaths were attributable to them in industrialized countries. More than 96% of global deaths by communicable diseases were also from developing countries. Respiratory infections ranked first in communicable morbidity at all ages. Even though vaccines of bacterial or viral origin or a prophylactic for passive immunization are produced in 24, 16 and 15 developing countries, respectively, none of the developing countries manufactures a plasma-derived prophylactic or biological response modifier. Nearly every country relies on import of one or more vaccines. The suboptimal performance of otherwise meritorious products has been due to faulty vaccine administration practices. Expanding populations, poverty and lack of education, cold-chain defects, and inadequate facilities for transport of vaccines to target populations in remote areas have been responsible for the poor performance of vaccines in the community. Mounting foreign debts and budgetary strains resulting from the care and prevention of AIDS/HIV have considerably strained national and international efforts to offer routine vaccinations in childhood and pregnancy. This dismal situation could be tackled through research to obtain environmentally stable products for prophylactic use and monoclonal antibody formulations for passive immunization, and through international financial and technical support. All countries should exercise some technical control of the quality of imported and indigenous vaccines during their use for curative or prophylactic purposes. The involvement of private clinicians in immunizations would strengthen national efforts for control of communicable diseases including AIDS, but this is not enough if the local factors cited above are not improved.

[Advances in rabies research]

Recent advances in research into rabies, based on the technological process of the biological sciences mainly molecular biology and genetic engineering, are mentioned. The current knowledge of the characteristics, properties pathogeny and immunology of the rabies views is presented, as well as the development of new diagnostic and vaccine evaluation techniques. The epidemiological importance of the identification of different immunogenic rabies virus strains and the role in immunoprophylaxis of the production of highly immunogenic vaccines, are set out.

Evaluation of the new serum-free medium (MDSS2) for the production of different biologicals: use of various cell lines

The presence of serum in cell culture raises safety problems for the production of biologicals, thus a new serum-free medium (MDSS2) was developed. The evaluation of this medium for the growth of different cell lines (BHK-21 C13, BSR and Vero) has shown that cells grew in this medium similarly to standard serum-containing medium, independently of the culture system used: in static (as monolayer) as well as in agitated systems (in suspension in spinner and perfusion reactors). BHK-21 and BSR cells grew as aggregate cultures and could proliferate in both static and agitated culture systems. Vero cells stayed attached to a substrate and proliferated equally in static and in agitated microcarrier-culture systems. The cell densities obtained with BHK-21 cells depended only on the culture system used. They ranged from 2-3 x 10(6) to 6-12 x 10(6) cells per ml for static batch and perfusion reactor cultures respectively. The cell concentration was 3 to 6 times higher than in classical cultures performed in serum-containing medium. The cell densities obtained with Vero cells were indistinguishable from those obtained in serum-containing medium, whatever the cell culture system used. These cell lines have been used for the production of rabies virus. With respect to BHK-21 and BSR, similar production rates of rabies glycoprotein have been found as in the standard roller bottle process. The production of rabies virus and of viral glycoprotein by Vero cells cultivated in serum-free medium was augmented 1.5-fold and 2.5-fold, respectively, when compared to serum-containing medium. A recombinant BHK-21 cell line, producing human IL-2, can also proliferate in MDSS2, after addition of insulin. The specific IL-2 production rate was augmented 3-4-fold in comparison to serum-containing medium. For the cells tested, the MDSS2 serum-free medium is a good growth and production medium. Its use for cultivating other cell lines and/or for the production of other biologicals is discussed.