Rapid diagnosis of rabies infection by means of a dot hybridization assay

Detection of rabies virus antigen in dog saliva using a latex agglutination test

Dog bites are responsible for more than 90% of human rabies deaths in Asia. We developed a simple and inexpensive test based on latex agglutination (LA) for rabies virus antigen detection in dog saliva. Rabies virus antigen could be detected by agglutination on a glass slide using latex particles coated with gamma globulin. By evaluation of paired saliva-brain specimens from 238 dogs, the LA test using saliva was 99% specific and 95% sensitive compared to the fluorescent antibody test (FAT) on brain smears. The advantages of the LA test over the standard FAT are that it is comparatively simple and there is no need to kill the animal before examination.

In vivo and in vitro detection of canine distemper virus nucleoprotein gene with digoxigenin-labelled RNA, double-stranded DNA probes and oligonucleotides by in situ hybridization

A single-stranded RNA, two double-stranded (ds) DNA probes and 10 oligonucleotides labelled with digoxigenin were comparatively evaluated for their usefulness to detect canine distemper virus (CDV) nucleoprotein RNA in in vitro infected Vero cells and in tissues of dogs with spontaneous CDV infection by in situ hybridization (ISH). In addition, results were compared to CDV nucleoprotein antigen distribution as demonstrated by immunohistochemistry. The RNA probe was derived from the virulent A75/17 strain, the DNA and oligonucleotide probes from the avirulent Onderstepoort strain of CDV. The two DNA probes were 287 and 126 base pairs long. For ISH, various factors including fixatives, proteolytic digestion, probe concentration, hybridization conditions and detection systems were compared. All probes were suitable for demonstration of CDV RNA in in vitro infected cells, regardless of the CDV strain employed. In vivo CDV nucleic acid was detected by RNA and the dsDNA probes. However, the probes varied substantially with respect to sensitivity and specificity. The CDV RNA probe was far superior in sensitivity when compared to the DNA probes. Furthermore, the shorter DNA probe displayed a higher sensitivity, indicating that length of the probe is an important parameter when selecting probes. Oligonucleotides displayed only rarely a positive signal and caused frequently hybridization signals in the nucleus, which where considered not specific for CDV. Summarized, the present study reveals that RNA probes are currently the most sensitive tool for detection of CDV RNA in tissues.

Rabies virus selectively alters 5-HT1 receptor subtypes in rat brain

Rabies virus infection in man induces a series of clinical symptoms, some suggesting involvement of the central serotonergic system. The results of the present study show that, 5 days after rabies virus infection in rat, the total reversible high-affinity binding of [3H]5-HT in the hippocampus is not affected, suggesting that 5-HT1A binding is not altered. 5-HT1B sites identified by [125I]cyanopindolol binding are not affected in the cortex 3 and 5 days after the infection. Accordingly, the cellular inhibitory effect of trifluoromethylphenylpiperazine (TFMPP) on the [3H]acetylcholine-evoked release, presumably related to 5-HT1B receptor activity, is not modified 3 days after infection. In contrast, [3H]5-HT binding determined in the presence of drugs masking 5-HT1A, 5-HT1B and 5-HT1C receptors, is markedly (50%) reduced 3 days after the viral infection. These results suggest that 5-HT1D-like receptor subtypes may be affected specifically and at an early stage after rabies viral infection.

Effects of post-mortem autolysis on the detection of rabies virus genomic RNA and mRNA in mouse brain by using in situ hybridization

The effects of post-mortem autolysis were studied on the detection of rabies virus RNA in the brains of mice with experimental rabies by using in situ hybridization (ISH). The brains of CVS-infected mice were subjected to autolytic periods in situ of up to 72 h. ISH was performed with 3H-labelled RNA probes for rabies virus glycoprotein gene genomic RNA and mRNA. During the post-mortem period there was progressive loss of signals for genomic RNA and mRNA, which was greater for mRNA. ISH signals in perikarya also changed for genomic RNA from a multifocal to a diffuse distribution during the post-mortem period. Rabies virus antigen was better preserved during the autolytic period. Effects of the agonal state, degradation of RNA by ribonucleases, and diffusion of RNA out of cells prior to fixation could explain the loss of ISH signals in post-mortem tissues.

PCR technique as an alternative method for diagnosis and molecular epidemiology of rabies virus

We have investigated the PCR amplification technique of viral nucleic acids as an alternative protocol for diagnosis and epidemiological studies of rabies virus. A primer set mapping in the nucleoprotein cistron allowed a specific and sensitive amplification of infected brain material, fulfilling the diagnosis requirements. One hundred samples checked by Southern or dot-blot analysis using both radioactive and non-radioactive probes showed identical results in parallel with routine techniques. For molecular epidemiological studies we selected another set of conserved primers flanking the highly evolutive pseudogene (psi gene) region. This set was found to be efficient for all tested fixed rabies virus strains or wild rabies virus isolates as well as the rabies-related Mokola virus. We describe a progressive characterization of the strain that could be extended from rapid typing by a limited panel of restriction enzymes, to the ultimate identification of the nucleotide sequence by an original direct sequencing technique of amplified segments.

Detection of rabies virus genomic RNA and mRNA in mouse and human brains by using in situ hybridization

Rabies virus RNA was detected in mouse and human brains by in situ hybridization. 3H-labeled single-stranded RNA probes were prepared which were specific for genomic RNA and mRNAs coding for the five rabies virus proteins (N, NS, M, G, and L). Paraffin-embedded brain tissues from human cases of rabies and mice experimentally infected with the challenge virus standard (CVS)-11 strain of rabies virus and street rabies virus were examined. In CVS-infected mice, genomic RNA had a multifocal distribution in the perikarya of infected neurons, perhaps reflecting concentration of genomic RNA in viral factories. The mRNAs were more abundant than genomic RNAs in CVS- and street virus-infected mouse brains and had a diffuse distribution in the perikarya. Similar amounts of signal were present in infected neurons for mRNAs coding for different rabies virus proteins. In brain tissues from human cases of rabies, genomic RNA was much more abundant than the mRNAs in infected neurons. This finding suggests either a relative block at the level of transcription or greater loss of mRNAs than of genomic RNA during the agonal period, postmortem interval, or prior to penetration of fixative during immersion fixation.

Polymerase chain reaction amplification of rabies virus nucleic acids from total mouse brain RNA

In an attempt to improve the sensitivity of the rabies genome hybridization test, PCR amplification was used following reverse transcription of rabies RNA extracted from infected brain. Presence of amplified DNA is demonstrated with either cDNA synthesized from the antigenomic primer or from antimessenger primer.

Detection of rabies virus RNA in the central nervous system of experimentally infected mice using in situ hybridization with RNA probes

Rabies virus is usually demonstrated in human or animal tissues using antigen-detection or viral isolation techniques. Rabies virus RNA can be demonstrated in paraffin-embedded tissues using in situ hybridization. Negative (-) sense 35S- and 3H-labeled RNA probes, specific for rabies virus nucleocapsid protein mRNA, were used for the detection of rabies virus RNA in the nervous system of mice experimentally infected with fixed and street strains of rabies virus. In situ hybridization signals were compared with rabies virus antigen demonstrated with immunoperoxidase staining. Rabies virus RNA and antigen were also demonstrated in the same neurons using a double-labeling technique. In situ hybridization has potential applications as a diagnostic test for rabies and in studies of rabies pathogenesis.

Comparative field evaluation of the fluorescent-antibody test, virus isolation from tissue culture, and enzyme immunodiagnosis for rapid laboratory diagnosis of rabies

The rabies tissue culture infection test (RTCIT) and rapid rabies enzyme immunodiagnosis (RREID) were compared to the fluorescent-antibody test (FAT) with field specimens. At the French National Reference Center for Rabies, 15,248 specimens were analyzed by FAT and RTCIT, and 2,290 of those specimens were also tested by RREID; 818 other specimens were tested by FAT and RREID in 12 laboratories located in Africa, Asia, and Latin America. The sensitivities and specificities of RREID and RTCIT were comparable. This study showed that both tests can be used as backup procedures to confirm FAT. RREID is also strongly recommended for epidemiological studies and for laboratories which are not equipped for performing FAT.