Procedures for reproducible detection of rabies virus antigen mRNA and genome in situ in formalin-fixed tissues

Diagnostic sensitivity and specificity of immunohistochemistry for the detection of rabies virus in domestic and wild animals in South Africa

We estimated the diagnostic sensitivity (DSe) and specificity (DSp) of an immunohistochemistry (IHC) protocol compared to the direct fluorescent antibody test (DFAT), which is the gold standard test for rabies diagnosis. We obtained brain samples from 199 domestic and wild animal cases (100 DFAT-negative, 99 DFAT-positive), by convenience sampling from 2 government-accredited rabies virus (RABV) testing laboratories in South Africa, between February 2015 and August 2017. Tissues that had been stored at 4-8°C for several days to weeks at the 2 accredited laboratories were formalin-fixed and paraffin-embedded. Nighty-eight cases tested IHC-positive using a polyclonal anti-RABV nucleoprotein antibody and a polymer detection system. The overall DSe and DSp for the RABV IHC test were 98% (95% CI: 93-100%) and 99% (95% CI: 95-100%), respectively. Domestic dogs accounted for 41 of 98 RABV IHC-positive cases, with the remainder in 4 domestic cats, 25 livestock, and 28 wildlife. Herpestidae species, including 7 meerkats and 9 other mongoose species, were the most frequently infected wild carnivores, followed by 11 jackals. Three cases in domestic dogs had discordant test results; 2 cases were IHC-/DFAT+ and 1 case was IHC+/DFAT-. Considering the implications of a false-negative rabies diagnosis, participating in regular inter-laboratory comparisons is vital, and a secondary or confirmatory method, such as IHC, should be performed on all submitted specimens, particularly negative cases with human contact history.

Virological investigation of fatal rabies in a minor bitten by a mongrel in Nigeria

Rabies is a deadly viral disease transmitted through bites of infected animals. Outbreaks continue to escalate in Africa, with fatalities in humans, especially in rural areas, but are rarely reported. About 40% casualties occur among children of < 15 years. A 5-year-old boy on referral from a Primary Health Care Centre to a tertiary hospital presented with anxiety, confusion, agitation, hydrophobia, photo-phobia and aero-phobia, seven weeks after he was bitten by a stray dog in a rural community in Nigeria. The patient did not receive post-exposure prophylaxis and died 48 hours post admission. Confirmatory diagnosis was rabies and the phylogenetic analysis of the partial N-gene sequence of the virus localized it to Africa 2 (genotype 1) Lyssaviruses. There was 95.7-100% and 94.9-99.5% identity between the isolate and other genotype 1 Lyssaviruses and 100% homology with rabies viruses from Mali, Burkina Faso, Senegal and Central African Republic.

Heat induced epitope retrieval for rabies virus detection by direct fluorescent antibody test in formalin-fixed dog brain tissues

There is a great need for a chemical method of tissue preservation that would allow sample storage for extended periods at room temperature. This study aimed at retrieving and detecting rabies virus antigen by direct fluorescent antibody test (DFAT) in formalin-fixed dog brain tissues. Forty fresh dog brain specimens were collected as paired samples from rabies suspected cases that were received for postmortem detection of rabies in the Central Diagnostic Laboratory, National Veterinary Research Institute, Vom. One portion of each paired sample was prepared for fresh fluorescent antibody testing and the other portion was prepared for epitope retrieval and florescent antibody testing following fixation in 10% neutral buffered formalin. DFAT on formalin-fixed tissue exhibited a sensitivity of 100% in comparison to DFAT on fresh-tissue. No false positive result was obtained in formalin-fixed DFAT procedure, demonstrating 100% specificity. There was no apparent difference in the intensity of fluorescence in DFAT on fresh sample and formalin-fixed DFAT following heat induced epitope retrieval (concordance = 98%; 95% C.I. 0.9660 to 0.9903). The strength of agreement between DFAT on formalin-fixed and DFAT on fresh tissue was very good (Cohen's kappa coefficient value= 1.000; 95% C.I. 1.000-1.000). This study provides new information on the retrieval of rabies antigen by heat induced epitope retrieval for DFAT on formalinized tissues. Formalin could therefore, be used henceforth to fix tissues of rabies suspected cases for routine diagnosis, transportation or archival purposes. The heat induced epitope retrieval can be routinely used to retrieve rabies virus antigen for DFAT in cases where only formalin-fixed tissues are available or when preservation by freezing is difficult.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

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.

Laboratory diagnosis of human rabies: recent advances

Rabies, an acute progressive, fatal encephalomyelitis, transmitted most commonly through the bite of a rabid animal, is responsible for an estimated 61,000 human deaths worldwide. The true disease burden and public health impact due to rabies remain underestimated due to lack of sensitive laboratory diagnostic methods. Rapid diagnosis of rabies can help initiate prompt infection control and public health measures, obviate the need for unnecessary treatment/medical tests, and assist in timely administration of pre- or postexposure prophylactic vaccination to family members and medical staff. Antemortem diagnosis of human rabies provides an impetus for clinicians to attempt experimental therapeutic approaches in some patients, especially after the reported survival of a few cases of human rabies. Traditional methods for antemortem and postmortem rabies diagnosis have several limitations. Recent advances in technology have led to the improvement or development of several diagnostic assays which include methods for rabies viral antigen and antibody detection and assays for viral nucleic acid detection and identification of specific biomarkers. These assays which complement traditional methods have the potential to revolutionize rabies diagnosis in future.

Evaluation of a rapid immunodiagnostic test kit for rabies virus

A rapid immunodiagnostic test kit for rabies virus detection was evaluated using 51 clinical samples and 4 isolates of rabies virus. The quick detection of rabies virus under field conditions may be helpful in determining if post-exposure prophylaxis is needed, thereby avoiding unnecessary treatments, as well as undue economic burden. There are several widely used diagnostic methods for rabies, including fluorescent antibody tests, reverse transcription polymerase chain reaction, and electron microscopy; however, these methods include time-consuming, intricate, and costly procedures. The rapid immunodiagnostic test was able to detect rabies virus in clinical samples, including brain tissue and saliva, in addition to 10(3.2) 50% lethal dose (LD(50))/mL cell-adapted rabies virus. The assay was not cross-reactive with non-rabies virus microbes. When the performance of the rapid immunodiagnostic test was compared to a fluorescent antibody test, the rapid immunodiagnostic test had a sensitivity of 91.7% and specificity of 100% (95.8% CI).

In situ localization of plethodontid courtship pheromone mRNA in formalin-fixed tissue

Male plethodontid salamanders produce courtship pheromones that increase female receptivity. Three protein components of the courtship pheromone cocktail have been characterized in the mental gland of Plethodon shermani, the red-legged salamander: plethodontid receptivity factor (PRF), plethodontid modulating factor (PMF), and sodefrin precursor-like factor (SPF). In this study, a streamlined in situ hybridization (ISH) protocol, employing a biotinylated oligonucleotide probe, is used to visualize the sites of pheromone expression in formalin-fixed paraffin-embedded P. shermani mental gland and post-cloacal tail tissue. Results corroborate previous RT-PCR studies on pheromone expression. PRF and PMF are highly expressed in P. shermani mental gland, while SPF expression is more variable. None of the tested pheromones is expressed in dorsal or ventral tail glands. The reported protocol is simple, rapid, and effective, allowing visualization of high-copy mRNA transcript in formalin-fixed tissue.

A simple method for detection of rabies viral sequences in 16-year old archival brain specimens with one-week fixation in formalin

Archival formalin-fixed and paraffin-embedded brain tissues are important source for diagnosis and molecular analysis. However, nucleic acids are particularly vulnerable to degradation during tissue processing. The brain cutting process usually is performed after 1 week of brain storage in formalin followed by embedding of each particular neuro-anatomical specimen in paraffin. A simple method of deparaffinization, proteinase K digestion and RNA extraction using the Boom technique to obtain rabies RNA in unbuffered, formalin-fixed and paraffin-embedded brain tissues kept at 30 degrees C for 16 years is described. Reverse transcription-polymerase chain reaction (RT-PCR) can be used to identify rabies viral N gene sequences of 150 bases in length in all patients, but not from every immunohistochemical (IHC)-positive specimen. Direct sequencing of 301bp of N gene was achieved in 4 of 7 patients. Results of sequencing a single sample of 1432 bases of N gene from a 24h processed formalin-fixed and paraffin-embedded rabies infected brain tissue after 1 month storage were in accord with those from frozen specimen analysis. It is strongly suggested that for further molecular analysis, a piece of fresh brain tissue should be saved prior to the brain sectioning process and stored no longer than 24h in formalin before embedding.

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.

Detection and strain differentiation of European bat lyssaviruses using in situ hybridisation

A protocol suitable for the detection of rabies virus and the related European bat lyssaviruses type 1 and 2 is described. In situ hybridisation, employing digoxigenin labelled riboprobes was used for the detection of lyssavirus RNA in mouse-infected brain tissue. The principal advantage of this technique, compared to routine methods used for histopathology, is that this method is robust, highly sensitive, and specific for assessing the presence of RNA in different tissues. An additional advantage is that there is no longer any requirement for high laboratory bio-containment, once the tissue under investigation has been safely fixed. Using this method, both genomic and messenger RNA were detected. The ability to detect messenger RNA is indicative of the presence of replicating virus and therefore, this technique is a powerful diagnostic tool for the routine detection of strains of rabies virus including the European bat lyssaviruses.

Use of discriminatory probes for strain typing of formalin-fixed, rabies virus-infected tissues by in situ hybridization

An in situ hybridization (ISH) method has been developed to overcome difficulties encountered in the viral typing of formalin-fixed rabies virus-infected brain tissue. Rabies viruses representative of all strains normally encountered in diagnostic submissions throughout Canada, including 3 strains of terrestrial hosts (arctic fox, western skunk, mid-Atlantic raccoon), 10 strains circulating in several bat reservoirs (BBCAN1 to BBCAN7, LACAN, SHCAN, and MYCAN), and the Evelyn-Rokitniki-Abelseth (ERA) strain, used as an oral vaccine for fox rabies control in Ontario, were targeted. Partial phosphoprotein gene fragments generated from reverse transcription (RT)-PCR products of specimens of each viral type were molecularly cloned and used to produce negative-sense digoxigenin-labeled RNA transcripts. Conditions permitting the use of these transcripts as strain-specific probes were optimized by blotting analyses with RT-PCR amplicons generated with representative rabies viruses and by ISH applied to mouse brains inoculated with these strains. The successful application of this methodology to two rabies virus-positive specimens that were also identified by traditional methods and the retrospective typing of two archival rabies virus-positive equine specimens is described. This technique provides a typing regimen for rabies virus isolates submitted in a form that is normally recalcitrant to alternate typing strategies.

Isolation of total-RNA from formalin-fixed rat retina

The aim of this project was to establish a method for the purification of total-RNA from fixed rat-retina. Two different established methods were used for RNA purification, and successful isolation was verified with RT-PCR for amplification of beta-actin (two different product-lengths) and subsequent gel-electrophoresis. Total-RNA was successfully isolated from fixed rat-retina. The house keeping gene, beta-actin could be detected after fixing the retina either with 1% formalin or with 4% paraformaldehyde (PFA). Hexamer-primer based RT-PCR gave better results than the oligo-d(T)-primer based RT-PCR method. Both the 698 and 225 bp beta-actin-fragments could be successfully amplified, where amplification of the latter was more efficient. This approach shows that tissue fixation prior to RNA-isolation facilitates the rapid isolation of undamaged RNAs in tissues such as the retina, which are known to yield low levels of RNA and are vulnerable to RNases.

Rabies re-examined

Rabies is an acute, progressive, incurable viral encephalitis. The causative agents are neurotropic RNA viruses in the family Rhabdoviridae, genus Lyssavirus. Mammalian reservoirs include the Carnivora and Chiroptera, but rabid dogs still pose the greatest hazard worldwide. Viral transmission occurs mainly via animal bite, and once the virus is deposited in peripheral wounds, centripetal passage occurs towards the central nervous system. After viral replication, there is centrifugal spread to major exit portals, the salivary glands. The epidemiological significance of any host "carrier" state remains highly speculative. Although incubation periods average 1-3 months, disease occurrence days or years after exposure has been documented. Rabies should be suspected in patients with a concomitant history of animal bite and traditional clinical presentation, but a lack of such clues makes antemortem diagnosis a challenge. Pathogenetic mechanisms remain poorly understood, and current care entails palliative measures only. Current medical emphasis relies heavily on prevention of exposure and intervention before clinical onset. Prophylaxis encompasses thorough wound treatment, vaccine administration, and inoculation of rabies immunoglobulin. Although it is a major zoonosis, canine rabies can be eliminated, and application of new vaccine technologies permits significant disease control among wildlife species. Nevertheless, despite much technical progress in the past century, rabies is a disease of neglect and presents a modern public-health conundrum.

A comparative study of the fluorescent antibody test for rabies diagnosis in fresh and formalin-fixed brain tissue specimens

Many diagnostic methods have been used to detect rabies virus antigen. The preferred method for routine diagnosis of rabies in fresh or frozen brain tissues is the fluorescent antibody test (FAT). In this study, the FAT was used to evaluate the rabies status of fresh/frozen brain specimens from more than 800 rabies-suspected cases, in more than 14 different species of animals. A comparable brain specimen from each case was fixed in 10% buffered formalin and examined by the FAT. The evaluation of rabies status between fresh and formalin-fixed tissues was in agreement in more than 99.8% of the cases. When fresh tissue is not available for testing, these results validate the use of this procedure for routine diagnosis of rabies in formalin-fixed brain tissues.

Use of anti-glycoprotein monoclonal antibodies to characterize rabies virus in formalin-fixed tissues

Seventy anti-rabies virus monoclonal antibodies (Mabs) were tested for reactivity with rabies and rabies-related viruses in formalin-fixed (FF) tissues. Forty-three of the Mabs were directed against the glycoprotein and 27 were directed against the nucleocapsid as determined by enzyme immunoassays and neutralization tests. Twenty of the anti-glycoprotein Mabs and one of the anti-nucleocapsid Mabs reacted with the rabies challenge virus strain (CVS) in FF tissue. These 21 Mabs were screened against other lyssaviruses in FF tissues: five rabies virus strains (coyote, skunk, raccoon, red bat, and silver-haired bat), and four rabies-related viruses (Australian bat lyssavirus, Duvenhage virus, Lagos bat virus, and Mokola virus). One of the anti-glycoprotein Mabs was reactive with all the virus strains screened. Another of the anti-glycoprotein Mabs reacted with all of the rabies virus strains tested, but not with any of the rabies-related virus strains tested. The remaining Mabs had reactivity patterns that could be useful for characterizing lyssaviruses in FF tissues.