Ante- and post-mortem diagnosis of rabies using nucleic acid-amplification tests

Updates on Rabies virus disease: is evolution toward "Zombie virus" a tangible threat?

Human rabies disease is caused by Rabies Lyssavirus, a virus belonging to Rhabdoviridae family. The more frequent means of contagion is through bites of infected mammals (especially dogs, but also bats, skunks, foxes, raccoons and wolves) which, lacerating the skin, directly inoculate virus-laden saliva into the underlying tissues. Immediately after inoculation, the Rabies virus enters neural axons and migrates along peripheral nerves towards the central nervous system, where it preferentially localizes and injuries neurons of brainstem, thalamus, basal ganglia and spinal cord. After an initial prodromic period, the infection evolves towards two distinct clinical entities, encompassing encephalitic (i.e., “furious”; ~70-80% of cases) and paralytic (i.e., “dumb”; ~20-30% of cases) rabies disease. The former subtype is characterized by fever, hyperactivity, hydrophobia, hypersalivation, deteriorated consciousness, phobic or inspiratory spasms, autonomic stimulation, irritability, up to aggressive behaviours. The current worldwide incidence and mortality of rabies disease are estimated at 0.175×100,000 and 0.153×100,000, respectively. The incidence is higher in Africa and South-East Asia, nearly double in men than in women, with a higher peak in childhood. Mortality remains as high as ~90%. Since patients with encephalitic rabies remind the traditional image of “Zombies”, we need to think out-of-the-box, in that apocalyptic epidemics of mutated Rabies virus may be seen as an imaginable menace for mankind. This would be theoretically possible by either natural or artificial virus engineering, producing viral strains characterized by facilitated human-to-human transmission, faster incubation, enhanced neurotoxicity and predisposition towards developing highly aggressive behaviours. (www.actabiomedica.it)

Rabies virus infection in a 21-year-old male presenting with ascending paralysis after a bat scratch

A 21-year-old, previously healthy male presented to hospital following 1 week of bilateral asymmetric ascending paralysis, odynophagia, and dysphagia. Initial magnetic resonance imaging (MRI) of the spine revealed an abnormal increased T2 signal with predominant dorsal column involvement and sparing of white matter throughout the cervical cord and extending to T5. The initial presumptive diagnosis was an acute infectious, versus inflammatory, myelitis. On reviewing the history, family members recalled a bat scratch on the left hand, sustained months prior, for which the patient did not seek or receive post-exposure prophylaxis (PEP). Rabies virus (RABV) RNA was detected by quantitative reverse transcription polymerase chain reaction (RT-qPCR) in two saliva samples, while nuchal skin biopsy and cerebrospinal fluid (CSF) were negative. Serum was negative for RABV neutralizing antibody. Sequencing and phylogenetic analyses identified the infecting RABV as a variant associated with silver-haired bats. Following risk assessment of exposure, 67 health care workers and several family members were offered PEP.

Pomegranate-Inspired Silica Nanotags Enable Sensitive Dual-Modal Detection of Rabies Virus Nucleoprotein

The outbreak of rabies virus (RABV) in Asia and Africa has attracted widespread concern due to its 100% mortality rate, and RABV detection is crucial to its diagnosis and treatment. Herein, we report a sensitive and reliable strategy for the dual-modal RABV detection using pomegranate-shaped dendritic silica nanospheres fabricated with densely incorporated quantum dots (QDs) and horseradish peroxidase (HRP)-labeled antibody. The immunoassay involves the specific interaction between virus and nanospheres-conjugated antibody coupled with robust fluorescence signal originating from QDs and naked-eye discernible colorimetric signal on the oxTMB. The ultrahigh loading capacity of QDs enables the detection limit down to 8 pg/mL via fluorescence modality, a 348-fold improvement as compared with conventional enzyme-linked immunosorbent assay (ELISA). In addition, the detection range was from 1.20 × 10² to 2.34 × 10⁴ pg/mL by plotting the absorbance at 652 nm with RABV concentrations with a detection limit of 91 pg/mL, which is nearly 2 order of magnitude lower than that of the conventional ELISA. Validated with 12 brain tissue samples, our immunoassay results are completely consistent with polymerase chain reaction (PCR) results. Compared with the PCR assay, our approach requires no complex sample pretreatments or expensive instruments. This is the first report on RABV diagnosis using nanomaterials for colorimetry-based prescreening and fluorescence-based quantitative detection, which may pave the way for virus-related disease diagnosis and clinical analysis.

[Сases of human convalescence from rabies and lifetime diagnostics of lyssavirus encephalitis.]

Notwithstanding the availability of effective vaccines, 40 - 60 thousand rabies cases in humans are reported every year. Almost always the disease is fatal because therapeutic treatment of lyssavirus encephalitis has not been developed. Since 1970 the number of reports on rare cases of convalescence including those using experimental treatment protocols has been gradually increasing 20 cases of convalescence, "partial" convalescence or long-term survival of humans (1970-2015) were selected as they were complaint with laboratory criteria of active lyssavirus infection. Children and teenagers were predominant in the analyzed group (85%). The cases were irregularly spread between the continents: Asia - 6 cases, North America - 6 cases, Africa - 2 cases and Europe - 1 case. India and the USA were on the top of the list of countries by the number of described cases. More than 60% humans were infected from dogs, three cases got infection from bats and 2 cases were allegedly associated with an unknown lyssavirus and an unidentified infection source. 70% cases were vaccinated and 10% cases were treated with gamma globulin before the disease onset. Serological tests for detection of antibodies to lyssaviruses in cerebrospinal fluid of infected humans were typically used for diagnostic laboratory verification. Less than 30% IFA and PCR positives were obtained. Lyssaviruses were never detected. Only 4 convalescent patients were treated using experimental protocols. 80% cases demonstrated severe neurological consequences, four (may be more) patients died afterwards within the period from two months to four years. Different perspectives on prospects of Milwaukee protocol use and other therapeutic techniques are given.

Utility of rabies neutralizing antibody detection in cerebrospinal fluid and serum for ante-mortem diagnosis of human rabies

Background

Early ante-mortem laboratory confirmation of human rabies is essential to aid patient management and institute public health measures. Few studies have highlighted the diagnostic value of antibody detection in CSF/serum in rabies, and its utility is usually undermined owing to the late seroconversion and short survival in infected patients. This study was undertaken to examine the ante-mortem diagnostic utility and prognostic value of antibody detection by rapid fluorescent focus inhibition test (RFFIT) in cerebrospinal fluid (CSF)/serum samples received from clinically suspected human rabies cases from January 2015 to December 2017.

Methodology/Principal findings

Samples collected ante-mortem and post-mortem from 130 and 6 patients with clinically suspected rabies respectively, were received in the laboratory during the study period. Ante-mortem laboratory confirmation was achieved in 55/130 (42.3%) cases. Real time PCR for detection of viral nucleic acid performed on saliva, nuchal skin, brain tissue and CSF samples could confirm the diagnosis in 15 (27.2%) of the 55 laboratory confirmed cases. Ante-mortem diagnosis could be achieved by RFFIT (in CSF and/or serum) in 45 (34.6%) of the 130 clinically suspected cases, accounting for 81.8% of the total 55 laboratory confirmed cases. The sensitivity of CSF RFFIT increased with the day of sample collection (post-onset of symptoms) and was found to be 100% after 12 days of illness. Patients who had received prior vaccination had an increased probability of a positive RFFIT and negative PCR result. Patients who were positive by RFFIT alone at initial diagnosis had longer survival (albeit with neurological sequelae) than patients who were positive by PCR alone or both RFFIT and PCR.

Conclusions/Significance

Detection of antibodies in the CSF/serum is a valuable ante-mortem diagnostic tool in human rabies, especially in patients who survive beyond a week. It was also found to have a limited role as a prognostic marker to predict outcomes in patients.

Ante-mortem diagnosis of human rabies is essential for patient management and public health measures. The detection of virus specific antibodies in the CSF/serum of patients with suspected rabies is thought to have a limited diagnostic role owing to late seroconversion and short survival in rabies. We examined the diagnostic and prognostic utility of antibody detection by rapid fluorescent focus inhibition test (RFFIT) in CSF/serum samples received from clinically suspected human rabies cases (2015–2017). RFFIT (in CSF and/or serum) could confirm ante-mortem diagnosis in 45 (34.6%) of the 130 clinically suspected cases, accounting for 81.8% of the total 55 laboratory confirmed cases. The sensitivity of CSF RFFIT increased with the day of sample collection (post-onset of symptoms) and was found to be 100% after 12 days of illness. Patients who had received prior vaccination had an increased likelihood of a positive RFFIT and negative PCR result. Patients who were positive by RFFIT alone at initial diagnosis had longer duration of survival, although with poor functional outcomes. Antibody detection by RFFIT in CSF/serum was found to have a diagnostic utility especially in patients who survived beyond a week and a limited prognostic role in human rabies.

Molecular approach for ante-mortem diagnosis of rabies in dogs

Background & objectives:

The ante-mortem diagnosis of rabies is of great significance in establishing the status of infection in dogs, especially since they are involved in exposure to human beings. The present study was, therefore, undertaken to elucidate the most appropriate secretion/tissue for reliable diagnosis of rabies in 26 living dogs suspected to be rabid.

Methods:

In the present study 26 dogs suspected to have rabies were included for ante-mortem diagnosis of rabies in clinical samples of skin and saliva by molecular approach viz. heminested reverse-transcriptase polymerase chain reaction (HnRT-PCR). Skin and saliva samples were collected from 13 dogs each.

Results:

Of the 13 clinically suspected dogs, fluorescent antibody technique (FAT) confirmed rabies in nine cases of dogs. Of these nine true-positive dogs, eight cases could be confirmed by HnRT-PCR from skin. Of the other 13 dogs clinically suspected for rabies, FAT confirmed rabies in 10 cases. Of these 10 true-positive dogs, rabies was detected ante-mortem by HnRT-PCR from the saliva in seven dogs. Thus, rabies was detected from skin with 90 per cent sensitivity, 100 per cent specificity and 92.85 per cent accuracy. With saliva, rabies was detected with a sensitivity of 76.92 per cent, specificity of 100 per cent and accuracy of 62.50 per cent. The positive predictive values were 100 per cent for both skin and saliva samples while negative predictive values were 80 and 50 per cent, respectively.

Interpretation & conclusions:

Skin biopsy may be more appropriate clinical sample as compared to saliva for ante-mortem diagnosis of rabies in dogs. HnRT-PCR can be employed for molecular diagnosis of rabies from skin in live dogs.

Molecular epidemiology of rabies virus circulating in domestic animals in India

Rabies is a neglected viral zoonotic disease affecting humans, domestic and wild animals and is endemic in most parts of the India. Dog mediated rabies is more predominant than other forms of rabies and molecular epidemiology is poorly understood in both reservoir and susceptible hosts. In the present study, a total of 140 rabies suspected brain samples from different species of animals from different geographical regions of India were used. The samples were parallelly tested by direct fluorescent antibody test, reverse transcriptase PCR and real-time PCR. Thirty positive samples were subjected for partial nucleoprotein gene sequencing and phylogenetic analysis. On sequence and phylogenetic analysis, it was observed that all Indian rabies viruses belonged to classical rabies virus of genotype 1 of Lyssavirus and formed two distinct groups. The majority of isolates were in group-1 and are closely related to arctic/arctic like lineage, whereas group-II isolated are closely related to cosmopolitan lineage. These results indicated there is simultaneous existence of two distinct lineages of rabies viruses in Indian subcontinent. Further whole genome studies are needed for better understanding of molecular epidemiology of rabies virus circulating in animals for control and prevention of rabies in India.

Development of a quantitative real-time RT-PCR assay for detecting Taiwan ferret badger rabies virus in ear tissue of ferret badgers and mice

In 2013, the first case of Taiwan ferret badger rabies virus (RABV-TWFB) infection was reported in Formosan ferret badgers, and two genetic groups of the virus were distinguished through phylogenetic analysis. To detect RABV-TWFB using a sensitive nucleic acid-based method, a quantitative real-time reverse transcription polymerase chain reaction targeting the conserved region of both genetic groups of RABV-TWFB was developed. This method had a limit of detection (LOD) of 40 RNA copies/reaction and detected viral RNA in brain and ear tissue specimens of infected and dead Formosan ferret badgers and mice with 100% sensitivity and specificity. The mean viral RNA load detected in the ear tissue specimens of ferret badgers ranged from 3.89 × 10⁸ to 9.73 × 10⁸ RNA copies/g-organ, which was 111-fold to 2,220-fold lower than the concentration detected in the brain specimens, but 2,000-fold to 5,000-fold higher than the LOD of the assay. This highly sensitive technique does not require facilities or instruments complying with strict biosafety criteria. Furthermore, it is efficient, safe, and labor-saving as only ear specimens need be sampled. Therefore, it is a promising technique for epidemiological screening of Taiwan ferret badger rabies.

Multi-site evaluation of the LN34 pan-lyssavirus real-time RT-PCR assay for post-mortem rabies diagnostics

Rabies is a fatal zoonotic disease that requires fast, accurate diagnosis to prevent disease in an exposed individual. The current gold standard for post-mortem diagnosis of human and animal rabies is the direct fluorescent antibody (DFA) test. While the DFA test has proven sensitive and reliable, it requires high quality antibody conjugates, a skilled technician, a fluorescence microscope and diagnostic specimen of sufficient quality. The LN34 pan-lyssavirus real-time RT-PCR assay represents a strong candidate for rabies post-mortem diagnostics due to its ability to detect RNA across the diverse Lyssavirus genus, its high sensitivity, its potential for use with deteriorated tissues, and its simple, easy to implement design. Here, we present data from a multi-site evaluation of the LN34 assay in 14 laboratories. A total of 2,978 samples (1,049 DFA positive) from Africa, the Americas, Asia, Europe, and the Middle East were tested. The LN34 assay exhibited low variability in repeatability and reproducibility studies and was capable of detecting viral RNA in fresh, frozen, archived, deteriorated and formalin-fixed brain tissue. The LN34 assay displayed high diagnostic specificity (99.68%) and sensitivity (99.90%) when compared to the DFA test, and no DFA positive samples were negative by the LN34 assay. The LN34 assay produced definitive findings for 80 samples that were inconclusive or untestable by DFA; 29 were positive. Five samples were inconclusive by the LN34 assay, and only one sample was inconclusive by both tests. Furthermore, use of the LN34 assay led to the identification of one false negative and 11 false positive DFA results. Together, these results demonstrate the reliability and robustness of the LN34 assay and support a role for the LN34 assay in improving rabies diagnostics and surveillance.

Application and Comparative Evaluation of Fluorescent Antibody, Immunohistochemistry and Reverse Transcription Polymerase Chain Reaction Tests for the Detection of Rabies Virus Antigen or Nucleic Acid in Brain Samples of Animals Suspected of Rabies in India

Accurate and early diagnosis of animal rabies is critical for undertaking public health measures. Whereas the direct fluorescent antibody (DFA) technique is the recommended test, the more convenient, direct rapid immunochemistry test (dRIT), as well as the more sensitive, reverse transcription polymerase chain reaction (RT-PCR), have recently been employed for the laboratory diagnosis of rabies. We compared the three methods on brain samples from domestic (dog, cat, cattle, buffalo, horse, pig and goat) and wild (leopard, wolf and jackal) animals from various parts of India. Of the 257 samples tested, 167 were positive by all the three tests; in addition, 35 of the 36 decomposed samples were positive by RT-PCR. This is the first study in which such large number of animal samples have been subjected to the three tests simultaneously. The results confirm 100% corroboration between DFA and dRIT, buttress the applicability of dRIT in the simple and rapid diagnosis of rabies in animals, and reaffirm the suitability of RT-PCR for samples unfit for testing either by DFA or dRIT.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

A DNA Logic Gate Automaton for Detection of Rabies and Other Lyssaviruses

Immediate activation of biosensors is not always desirable, particularly if activation is due to non-specific interactions. Here we demonstrate the use of deoxyribozyme-based logic gate networks arranged into visual displays to precisely control activation of biosensors, and demonstrate a prototype molecular automaton able to discriminate between seven different genotypes of Lyssaviruses, including Rabies virus. The device uses novel mixed-base logic gates to enable detection of the large diversity of Lyssavirus sequence populations, while an ANDNOT logic gate prevents non-specific activation across genotypes. The resultant device provides a user-friendly digital-like, but molecule-powered, dot-matrix text output for unequivocal results read-out that is highly relevant for point of care applications.

Enhanced diagnosis of rabies and molecular evidence for the transboundary spread of the disease in Mozambique

Rabies is a neglected zoonotic disease with veterinary and public health significance, particularly in Africa and Asia. The current knowledge of the epidemiology of rabies in Mozambique is limited because of inadequate sample submission, constrained diagnostic capabilities and a lack of molecular epidemiological research. We wanted to consider the direct, rapid immunohistochemical test (DRIT) as an alternative to the direct fluorescent antibody (DFA) for rabies diagnosis at the diagnostic laboratory of the Central Veterinary Laboratory (CVL), Directorate of Animal Science, Maputo, Mozambique. Towards this aim, as a training exercise at the World Organisation for Animal Health (OIE) Rabies Reference Laboratory in South Africa, we performed the DRIT on 29 rabies samples from across Mozambique. With the use of the DRIT, we found 15 of the 29 samples (52%) to be negative. The DRIT-negative samples were retested by DFA at the OIE Rabies Reference Laboratory, as well as with an established real-time Polymerase chain reaction, confirming the DRIT-negative results. The DRIT-positive results (14/29) were retested with the DFA and subsequently amplified, sequenced and subjected to phylogenetic analyses, confirming the presence of rabies RNA. Molecular epidemiological analyses that included viruses from neighbouring countries suggested that rabies cycles within Mozambique might be implicated in multiple instances of cross-border transmission. In this regard, our study has provided new insights that should be helpful in informing the next steps required to better diagnose, control and hopefully eliminate rabies in Mozambique.

Perspectives in Diagnosis and Treatment of Rabies Viral Encephalitis: Insights from Pathogenesis

Rabies viral encephalitis, though one of the oldest recognized infectious disease of humans, remains an incurable, fatal encephalomyelitis, despite advances in understanding of its pathobiology. Advances in science have led us on the trail of the virus in the host, but the sanctuaries in which the virus remains hidden for its survival are unknown. Insights into host-pathogen interactions have facilitated evolving immunologic therapeutic strategies, though we are far from a cure. Most of the present-day knowledge has evolved from in vitro studies using fixed (attenuated) laboratory strains that may not be applicable in the clinical setting. Much remains to be unraveled about this elusive virus. This review attempts to re-examine the current advances in understanding of the pathobiology of the rabies virus that modulate the diagnosis, treatment, and prevention of this fatal disease.

Dual Combined Real-Time Reverse Transcription Polymerase Chain Reaction Assay for the Diagnosis of Lyssavirus Infection

The definitive diagnosis of lyssavirus infection (including rabies) in animals and humans is based on laboratory confirmation. The reference techniques for post-mortem rabies diagnosis are still based on direct immunofluorescence and virus isolation, but molecular techniques, such as polymerase chain reaction (PCR) based methods, are increasingly being used and now constitute the principal tools for diagnosing rabies in humans and for epidemiological analyses. However, it remains a key challenge to obtain relevant specificity and sensitivity with these techniques while ensuring that the genetic diversity of lyssaviruses does not compromise detection. We developed a dual combined real-time reverse transcription polymerase chain reaction (combo RT-qPCR) method for pan-lyssavirus detection. This method is based on two complementary technologies: a probe-based (TaqMan) RT-qPCR for detecting the RABV species (pan-RABV RT-qPCR) and a second reaction using an intercalating dye (SYBR Green) to detect other lyssavirus species (pan-lyssa RT-qPCR). The performance parameters of this combined assay were evaluated with a large panel of primary animal samples covering almost all the genetic variability encountered at the viral species level, and they extended to almost all lyssavirus species characterized to date. This method was also evaluated for the diagnosis of human rabies on 211 biological samples (positive n = 76 and negative n = 135) including saliva, skin and brain biopsies. It detected all 41 human cases of rabies tested and confirmed the sensitivity and the interest of skin biopsy (91.5%) and saliva (54%) samples for intra-vitam diagnosis of human rabies. Finally, this method was successfully implemented in two rabies reference laboratories in enzootic countries (Cambodia and Morocco). This combined RT-qPCR method constitutes a relevant, useful, validated tool for the diagnosis of rabies in both humans and animals, and represents a promising tool for lyssavirus surveillance.

The Pan-African Rabies Control Network (PARACON): A unified approach to eliminating canine rabies in Africa

Even though Africa has the highest per capita death rate from rabies of any continent, and the disease is almost entirely transmitted by the bites of rabid dogs, there has been no coordinated pan-African approach to controlling canine rabies. In order to attain an inclusive and unified network, the Pan-African Rabies Control Network (PARACON) was established in 2014. By following the 'One Health' concept, which involves close coordination between animal and human health sectors across national, regional and continental levels, PARACON will provide a platform to facilitate and promote coordinated and sustainable control strategies and programmes. Meetings will take place at regular intervals and will be centred on the involvement by key focal persons from the medical and veterinary sectors. The inaugural meeting was held in South Africa in June, 2015 and was focused around interactive discussions and workshops, whilst updating country representatives on the tools available to aid them in developing and implementing sustainable rabies intervention strategies. Experts from various global organizations, institutions and industry participated in the discussions and shared their experience and expertise. The workshops focused on the latest format of the Rabies Blueprint platform (www.rabiesblueprint.com), which in the broadest sense assists with control and elimination campaigns, including educational and advocacy drives, improvement of surveillance and diagnosis and the systematic monitoring of progress. Together with the Stepwise Approach towards Rabies Elimination, the Blueprint is a planning tool to help countries free themselves from canine-transmitted rabies.

Instructive even after a decade: Complete results of initial virological diagnostics and re-evaluation of molecular data in the German rabies virus "outbreak" caused by transplantations

In 2005, six patients in Germany received solid organs and both corneas from a donor with an unrecognized rabies infection. Initial virological diagnostics with the machinery available at the two national reference laboratories could quickly clarify the situation. Rabies virus antigen was detected in the organ donor's brain. In two of the three recipients with neurological alterations, intra vitam diagnosis was achieved by conventional RT-PCRs. Comparison of the phylogenetic relatedness of the different viral isolates proved transmission from the donor and, consequently, also established the diagnosis for the third patient. As indicated by the titre of neutralizing antibodies, the liver transplant recipient was protected from the lethal infection due to a vaccination against rabies virus, which he had received more than 15 years ago. All samples from the recipients of the corneas were invariably negative. Re-evaluation of the molecular data by real-time PCR did not lead to an improvement of intra vitam diagnosis but provided intriguing insights regarding the relative amounts of rabies virus RNA in different body fluids and peripheral organs. In saliva and skin, they were 250-200,000 times lower than in the infected patient's brains. Furthermore, in saliva samples taken serially from the same patient fluctuations by a factor of 160-500 were recorded. These findings highlight the problems of intra vitam diagnosis of rabies virus infections and make understandable why the virus can escape from all diagnostic attempts. Finally, in this context one should recall an almost trivial fact: Simple and appropriate postexposure prophylaxis could not only have saved the young organ donor's life but would also have prevented the whole transplantation-associated rabies "outbreak" in Germany.

Real-Time RT-PCR for the Detection of Lyssavirus Species

The causative agents of rabies are single-stranded, negative-sense RNA viruses in the genus Lyssavirus of Rhabdoviridae, consisting of twelve classified and three as yet unclassified species including classical rabies virus (RABV). Highly neurotropic RABV causes rapidly progressive encephalomyelitis with nearly invariable fatal outcome. Rapid and reliable diagnosis of rabies is highly relevant for public and veterinary health. Due to growing variety of the genus Lyssavirus observed, the development of suitable molecular assays for diagnosis and differentiation is challenging. This work focused on the establishment of a suitable real-time RT-PCR technique for rabies diagnosis as a complement to fluorescent antibody test and rabies tissue culture infection test as gold standard for diagnosis and confirmation. The real-time RT-PCR was adapted with the goal to detect the whole spectrum of lyssavirus species, for nine of which synthesized DNA fragments were used. For the detection of species, seven probes were developed. Serial dilutions of the rabies virus strain CVS-11 showed a 100-fold higher sensitivity of real-time PCR compared to heminested RT-PCR. Using a panel of thirty-one lyssaviruses representing four species, the suitability of the protocol could be shown. Phylogenetic analysis of the sequences obtained by heminested PCR allowed correct classification of all viruses used.

Comparison of biotinylated monoclonal and polyclonal antibodies in an evaluation of a direct rapid immunohistochemical test for the routine diagnosis of rabies in southern Africa

The major etiological agent of rabies, rabies virus (RABV), accounts for tens of thousands of human deaths per annum. The majority of these deaths are associated with rabies cycles in dogs in resource-limited countries of Africa and Asia. Although routine rabies diagnosis plays an integral role in disease surveillance and management, the application of the currently recommended direct fluorescent antibody (DFA) test in countries on the African and Asian continents remains quite limited. A novel diagnostic assay, the direct rapid immunohistochemical test (dRIT), has been reported to have a diagnostic sensitivity and specificity equal to that of the DFA test while offering advantages in cost, time and interpretation. Prior studies used the dRIT utilized monoclonal antibody (MAb) cocktails. The objective of this study was to test the hypothesis that a biotinylated polyclonal antibody (PAb) preparation, applied in the dRIT protocol, would yield equal or improved results compared to the use of dRIT with MAbs. We also wanted to compare the PAb dRIT with the DFA test, utilizing the same PAb preparation with a fluorescent label. The PAb dRIT had a diagnostic sensitivity and specificity of 100%, which was shown to be marginally higher than the diagnostic efficacy observed for the PAb DFA test. The classical dRIT, relying on two-biotinylated MAbs, was applied to the same panel of samples and a reduced diagnostic sensitivity (83.50% and 90.78% respectively) was observed. Antigenic typing of the false negative samples indicated all of these to be mongoose RABV variants. Our results provided evidence that a dRIT with alternative antibody preparations, conjugated to a biotin moiety, has a diagnostic efficacy equal to that of a DFA relying on the same antibody and that the antibody preparation should be optimized for virus variants specific to the geographical area of focus.

Effects of carcase decomposition on rabies virus infectivity and detection

Carcases received for rabies diagnosis are occasionally decomposed due to delays in finding, submitting or storing them. Positive diagnostic results from such samples are reliable but negative results may be invalid. Previous studies assessed the effect of decomposition on rabies detection using excised brains. To better reflect decomposition in the field, intact infected mouse carcases were stored at three temperatures for up to 70 days. The brains were then removed and tested using routine rabies diagnostic assays. Rabies virus was isolated using the Rabies Tissue Culture Inoculation Test (RTCIT) on days 18, 3 and 3 at 4°C, 25°C and 35°C, respectively. The Fluorescent Antibody Test (FAT) detected viral antigen on days 36, 12 and 3, whilst a rabies specific Hemi-nested RT-PCR detected viral RNA on days 70, 48 and 48 at 4°C, 25°C and 35°C, respectively. These findings suggest the persistence of infectious rabies virus in carcases left for 18 days at cold temperatures (4°C) and up to 3 days in temperatures reaching 35°C. The detection of viral RNA from a carcase decomposing at 35°C for 48 days supports the use of molecular assays to accompany OIE-prescribed rabies diagnostic tests particularly when decomposed samples are likely to be submitted. Count=199.

Biotechnology advances: a perspective on the diagnosis and research of Rabies Virus

Rabies is a widespread zoonotic disease responsible for approximately 55,000 human deaths/year. The direct fluorescent antibody test (DFAT) and the mouse inoculation test (MIT) used for rabies diagnosis, have high sensitivity and specificity, but are expensive and time-consuming. These disadvantages and the identification of new strains of the virus encourage the use of new techniques that are rapid, sensitive, specific and economical for the detection and research of the Rabies Virus (RABV). Real-time RT-PCR, phylogeographic analysis, proteomic assays and DNA recombinant technology have been used in research laboratories. Together, these techniques are effective on samples with low virus titers in the study of molecular epidemiology or in the identification of new disease markers, thus improving the performance of biological assays. In this context, modern advances in molecular technology are now beginning to complement more traditional approaches and promise to revolutionize the diagnosis of rabies. This brief review presents some of the recent molecular tools used for RABV analysis, with emphasis on rabies diagnosis and research.

Simultaneous detection and differentiation of human papillomavirus genotypes 6, 11, 16 and 18 by AllGlo quadruplex quantitative PCR

Background

Human papillomaviruses (HPV) are classified into high-risk HPV and low-risk HPV. The most common high-risk HPV types in cervical cancer are HPV 16 and 18, and the most common low-risk types causing genital warts are HPV 6 and HPV 11. In this study, applying novel AllGlo fluorescent probes, we established a quadruplex quantitative PCR method to simultaneously detect and differentiate HPV 6, 11, 16 and 18 in a single tube.

Methods

The specificity, the sensitivity, the detection limit, the reproducibility and the standard curve of this method were examined. Finally, clinical samples that had been tested previously by TaqMan PCR and HPV GenoArray (GA) test were used to verify the accuracy and sensitivity of the method.

Results

The assay has a sensitivity of 10¹ to 10² copies/test and a linear detection range from 10¹ to 10⁸ copies/test. The mean amplification efficiencies for HPV 6, 11, 16, and 18 were 0.97, 1.10, 0.93 and 1.20, respectively, and the mean correlation coefficient (r²) of each standard curve was above 0.99 for plasmid templates ranging from 10³ to 10⁷ copies/test. There was 100% agreement between the AllGlo quadruplex quantitative PCR, HPV GA test and TaqMan uniplex qPCR methods.

Conclusions

AllGlo quadruplex quantitative PCR in a single tube has the advantages of relatively high throughput, good reproducibility, high sensitivity, high specificity, and a wide linear range of detection. The convenient single tube format makes this assay a powerful tool for the studies of mixed infections by multiple pathogens, viral typing and viral load quantification.

Detection of rabies viral RNA by TaqMan real-time RT-PCR using non-neural specimens from dogs infected with rabies virus

To determine the burden of rabies in developing countries, a reliable and accurate diagnostic test for the examination of the brains of animals is needed. Recently, the number of samples and carcasses submitted to rabies diagnostic units has been declining. Methods for obtaining tissues from different regions of the brain are even more difficult, and direct florescent antibody examination may fail if the samples decomposed. The spread of rabies virus to peripheral non-nervous tissues starts early during the pre-clinical phase. It has been shown that saliva and skin biopsies taken at the neck and containing hair follicles can be used in the ante-mortem diagnosis of rabies in humans. Obtaining oral swab samples, whisker or hair follicles from the heads of canines is easy and practical and can be performed without special equipment. The objective of this study was to determine whether these non-neural specimens can be used for the detection of rabies viral RNA. The RNAs extracted from these specimens were tested using a real-time reverse transcriptase polymerase chain reaction (RT-PCR). The sensitivity of the TaqMan real-time RT-PCR analysis using samples from dogs confirmed to be infected with rabies virus was 84.6% (55/65), 81.8% (54/66) and 66.7% (44/66) when using oral swab samples, extracted whisker follicles and extracted hair follicles; the specificity of all specimen types was 100%. The negative predictive values were 77.8%, 74.4% and 61.4%, respectively. Although the rate of positivity when combining the three non-neural specimen types was increased to 86.4%, this level of sensitivity was not sufficient to help physicians whether to administer post exposure prophylaxis. However, these oral swab and whisker specimens may serve to enhance epidemiological surveillance; such data will contribute in the planning of rabies control programs.

Rabies in Asia: the classical zoonosis

Rabies remains a constant threat to humans throughout much of Asia. The dog is the main reservoir and vector with wildlife playing a very minor role. No Asian country or region has been declared rabies free by WHO in over two decades and there is evidence of canine rabies spread to new regions during the past 10 years. We now have the knowledge and technology to control canine rabies. The main barrier in managing this costly endemic is lack of motivation by authorities to address this issue along with regional inability of public health and livestock (agriculture) officials to tackle this issue in cooperation and coordination. Rabies is one of the first recognized zoonoses and a model for a true "One Health" management goal where human; veterinary, and government officials must work together in harmony to defeat this disease.

Comparative detection of rabies RNA by NASBA, real-time PCR and conventional PCR

Five methods for the RNA detection of rabies virus were directly compared in this study. These included conventional nucleic acid sequence-based amplification with electrochemiluminescence (NASBA-ECL) assay, reverse transcription (RT)-heminested (hn) polymerase chain reaction (PCR) and TaqMan real-time RT-PCR using protocols as described previously. The first two methods have been routinely utilised for ante-mortem diagnosis of human rabies in Thailand and other rabies-endemic Asian and African countries. In addition, two real-time NASBA assays based on the use of a NucliSens EasyQ analyser (NASBA-Beacon-EQ) and LightCycler real-time PCR machine (NASBA-Beacon-LC) were studied in parallel. All methods target the N gene, whereas the L gene is used for RT-hnPCR. Using serial dilutions of purified RNA from rabies-infected dog brain tissue to assess sensitivity, all five methods had comparable degrees of sensitivities of detection. However, both real-time NASBA assays had slightly lower sensitivities by 10-fold than the other three assays. This finding was also true (except for TaqMan real-time RT-PCR due to a mismatch between the target and probe sequences) when laboratory-adapted (challenge virus standard-11) virus was used in the assays. Testing on previously NASBA-ECL positive clinical samples from 10 rabies patients (saliva [6] and brain [4]) and 10 rabies-infected dog brain tissues, similar results were obtained among the five methods; real-time NASBA assays yielded false-negative results on 2 saliva samples. None of the assays showed positive results on cerebrospinal fluid specimens of 10 patients without rabies encephalitis. Due to the unavailability of the NASBA-ECL assay, the results show that TaqMan real-time RT-PCR and RT-hnPCR can be useful for ante- and post-mortem diagnosis of rabies.

Lyssavirus detection and typing using pyrosequencing

Rabies is a fatal zoonosis caused by a nonsegmented negative-strand RNA virus, namely, rabies virus (RABV). Apart from RABV, at least 10 additional species are known as rabies-related lyssaviruses (RRVs), and some of them are responsible for occasional spillovers into humans. More lyssaviruses have also been detected recently in different bat ecosystems, thanks to the application of molecular diagnostic methods. Due to the variety of the members of the genus Lyssavirus, there is the necessity to develop a reliable molecular assay for rabies diagnosis able to detect and differentiate among the existing rabies and rabies-related viruses. In the present study, a pyrosequencing protocol targeting the 3' terminus of the nucleoprotein (N) gene was applied for the rapid characterization of lyssaviruses. Correct identification of species was achieved for each sample tested. Results from the pyrosequencing assay were also confirmed by those obtained using the Sanger sequencing method. A pan-lyssavirus one-step reverse transcription (RT)-PCR was developed within the framework of the pyrosequencing procedure. The sensitivity (Se) of the one-step RT-PCR assay was determined by using in vitro-transcribed RNA and serial dilutions of titrated viruses. The assay demonstrated high analytical and relative specificity (Sp) (98.94%) and sensitivity (99.71%). To date, this is the first case in which pyrosequencing has been applied for lyssavirus identification using a cheaper diagnostic approach than the one for all the other protocols for rapid typing that we are acquainted with. Results from this study indicate that this procedure is suitable for lyssavirus detection in samples of both human and animal origin.

Improved PCR methods for detection of African rabies and rabies-related lyssaviruses

Eleven different lyssavirus species, four of which occur on the African continent, are presently recognized. These viruses cause rabies, the burden of which is highest in the developing world, where routine laboratory diagnosis is often not available. From an epidemiological and control perspective, it is necessary that diagnostic methods detect the diversity of lyssaviruses present in different regions of the world. A published and widely used heminested reverse transcription-PCR (hnRT-PCR) was evaluated for its ability to detect a panel of diverse African lyssaviruses. Due to the limitations experienced for this assay, an alternative hnRT-PCR was developed. The new assay was found to be accurate and sensitive in the detection of African lyssavirus RNA in a variety of clinical specimens. The assay was further adapted to a real-time PCR platform to allow rapid, one-step, quantitative, and single-probe detection, and an internal control for the verification of sample preparation was included. The limit of detection of the real-time PCR assay was 10 RNA copies per reaction, with inter- and intra-assay variability below 4%. Subsequently, in demonstrating utility, both assays were successfully applied to antemortem rabies diagnosis in humans. We believe that the quantitative real-time PCR assay could find application as a routine confirmatory test for rabies diagnosis in the future and that it will serve as a valuable research tool in the biology of African lyssaviruses. Alternatively, the hnRT-PCR assay can be used in laboratories that do not have access to expensive real-time PCR equipment for sensitive diagnosis of lyssaviruses.

Comparative analysis of rabies virus reverse transcription-PCR and virus isolation using samples from a patient infected with rabies virus

Definite and rapid diagnosis of rabies is required for individual case management as well as for public health. For the first time, a direct comparison of virus isolation with quantitative real-time reverse transcription (RT)-PCR on human rabies samples was conducted. RT-PCR was found to be more sensitive than virus isolation.