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

Using the LN34 Pan-Lyssavirus Real-Time RT-PCR Assay for Rabies Diagnosis and Rapid Genetic Typing from Formalin-Fixed Human Brain Tissue

Human rabies post mortem diagnostic samples are often preserved in formalin. While immunohistochemistry (IHC) has been routinely used for rabies antigen detection in formalin-fixed tissue, the formalin fixation process causes nucleic acid fragmentation that may affect PCR amplification. This study reports the diagnosis of rabies in an individual from the Dominican Republic using both IHC and the LN34 pan-lyssavirus real-time RT-PCR assay on formalin-fixed brain tissue. The LN34 assay generates a 165 bp amplicon and demonstrated higher sensitivity than traditional PCR. Multiple efforts to amplify nucleic acid fragments larger than 300 bp using conventional PCR were unsuccessful, probably due to RNA fragmentation. Sequences generated from the LN34 amplicon linked the case to the rabies virus (RABV) strain circulating in the Ouest Department of Haiti to the border region between Haiti and the Dominican Republic. Direct sequencing of the LN34 amplicon allowed rapid and low-cost rabies genetic typing.

Detection of VHSV IVb within the gonads of Great Lakes fish using in situ hybridization

Viral haemorrhagic septicaemia virus (VHSV) genotype IVb was recently detected as the cause of numerous mortality events in Great Lakes fish. In situ hybridization was used to examine the gonads from 13 fish, including freshwater drum Aplodinotus grunniens and muskellunge Esox masquinongy that were infected naturally, as well as rainbow trout Oncorhynchus mykiss and fathead minnows Pimphales promelas, which were experimentally infected. Although the ovaries and testes of fish infected by VHSV IVb had few lesions, viral RNA was present in the ovaries of the rainbow trout and fathead minnow and was abundant in the gonads of muskellunge and in the ovaries of freshwater drum. Viral RNA was present mainly surrounding yolk vacuoles/granules or adjacent to the germinal vesicle, with lesser amounts found within the germinal vesicle, in the mesovarium and/or tunica albuginea and blood vessels of the ovary. Viral RNA was also found in and surrounding primary and secondary spermatocytes of the muskellunge.

Development of real-time reverse transcriptase polymerase chain reaction methods for human rabies diagnosis

To improve timely ante-mortem human rabies diagnosis, methods to detect viral RNA by TaqMan-based quantitative reverse transcriptase polymerase chain reactions (qRT-PCRs) have been developed. Three sets of two primers and one internal dual-labeled probe for each primer set that target distinct conserved regions of the rabies virus N gene were designed and evaluated. Using a collection of 203 isolates representative of the world-wide diversity of rabies virus, all three primers/probe sets were shown to detect a wide range of rabies virus strains with very few detection failures; the RABVD1 set in particular was the most broadly reactive. These qRT-PCR assays were shown to be quantitative over a wide range of viral titer and were 100-1,000 times more sensitive than nested RT-PCR; however, both the standard and real-time PCR methods yielded concordant results when used to test a collection of archived human suspect samples. The qRT-PCR assay was employed to monitor virus load in the saliva of a rabies virus-infected patient undergoing the Milwaukee treatment protocol. However in this case it would appear that reduction of the viral load in the patient's saliva over time did not appear to correlate well with clearance of viral components from the brain.

Detection of rabies virus genes by in-situ polymerase chain reaction

Rabies is diagnosed by FAT in the impression smears of brain tissues. In this study, an attempt was made to diagnose rabies using in situ polymerase chain reaction (ISPCR). A digoxigenin-labelled double-stranded probe specific for a portion of the 'N' gene of rabies virus was used. Positive signals were identified as blue dots in the intraneuronal and neuropil areas.

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.