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

Tioman virus infection in experimentally infected mouse brain and its association with apoptosis

Tioman virus is a newly described bat-urine derived paramyxovirus isolated in Tioman Island, Malaysia in 2001. Hitherto, neither human nor animal infection by this virus has been reported. Nonetheless, its close relationship to another paramyxovirus, the Menangle virus which had caused diseases in humans and pigs [Philbey, A.W., Kirkland, P.D., Ross, A.D., Davis, R.J., Gleeson, A.B., Love, R.J., Daniels, P.W., Gould, A.R., Hyatt, A.D., 1998. An apparently new virus (family Paramyxoviridae) infectious for pigs, humans, and fruit bats. Emerg. Infect. Dis. 4, 269-271], raises the possibility that it may be potentially pathogenic. In this study, mice were experimentally infected with Tioman virus by intraperitoneal and intracerebral routes, and the cellular targets and topographical distribution of viral genome and antigens were examined using in situ hybridization and immunohistochemistry, respectively. The possible association between viral infection and apoptosis was also investigated using the TUNEL assay and immunohistochemistry to FasL, Caspase-3, Caspase-8, Caspase-9 and bcl-2. The results showed that Tioman virus inoculated intracerebrally was neurotropic causing plaque-like necrotic areas, and appeared to preferentially replicate in the neocortex and limbic system. Viral infection of inflammatory cells was also demonstrated. TUNEL and Caspase-3 positivity was found in inflammatory cells but not in neurons, while FasL, Caspase-8 and Caspase-9 were consistently negative. This suggests that neuronal infection was associated with necrosis rather than apoptosis. Moreover, the data suggest that there may be an association between viral infection and apoptosis in inflammatory cells, and that it could, at least in part, involve Caspase-independent pathways. Bcl-2 was expressed in some neurons and inflammatory cells indicating its possible role in anti-apoptosis. There was no evidence of central nervous system infection via the intraperitoneal route.

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.

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.

Molecular epidemiology of enzootic rabies in California

BACKGROUND

Molecular characterization of rabies virus has been used to trace spillover transmission from reservoir species to non-reservoir animals and humans (molecular epidemiology), and to monitor emergence of specific strains of the virus into new species and geographic areas (molecular surveillance).

OBJECTIVES

To characterize the enzootic strains of rabies virus in California wildlife for epidemiological investigation of transmission to non-reservoir animals and humans.

STUDY DESIGN

Molecular characterization was performed on rabies strains from 213 bats, 276 terrestrial animals and one human case, by RT-PCR amplification of the viral nucleocapsid (N) gene followed by Dde I digestion and restriction endonuclease analysis (REA). Brain material from 88 terrestrial animals and 74 bats was stained with a panel of 20 monoclonal antibodies (MABs) directed against the N protein. In order to characterize rabies from very small quantities of brain tissue a nested RT-PCR was developed and evaluated for sensitivity of rabies detection.

RESULTS AND CONCLUSIONS

Enzootic terrestrial rabies in California is confined to the Central Valley, the western slope of the Sierra Nevada, and the Central and Northern Pacific Coast Ranges. No terrestrial reservoirs were identified south of the Tehachapi Mountains or east of the Sierra Nevada. Bat strains accounted for rabies in terrestrial animals in these regions. Among terrestrial rabies strains REA identified ten genotypes that segregated geographically and were associated with skunk and fox populations from distinct locations. Co-circulation of three genotypes occurred in Placer County, which had the highest incidence of rabies in skunks. In regions with terrestrial enzootic rabies, the strain from that region accounted for 73% of spillover cases. Bat strains accounted for the remaining 27%. Among terrestrial animals MABs identified three predominant patterns. In rabies strains from bats REA identified ten major and two minor patterns primarily associated with genus and species of bat. Sharing of strains between species was observed. An additional sixteen unclassified REA bat patterns were observed in only one or two individuals of various species. MABs identified four major patterns in bats associated with genus and species of bat with considerable variability. The bat strains most frequently detected in spillover cases throughout California were from the California myotis (Myotis californicus) and Mexican free-tailed bat (Tadarida brasiliensis). Nested RT-PCR increased the detection level of rabies virus 100,000-fold, to 0.03 TCID50.

Cyclooxygenase-2 is induced globally in infarcted human brain

Cyclooxygenase (COX) catalyzes synthesis of prostanoids after liberation of arachidonic acid, an important biochemical sequela of cerebral ischemia that aggravates brain injury. We investigated expression of inducible COX-2 in infarcted human brains (symptom duration, 15 hours to 18 days) and found that COX-2 protein was present in both neuronal and glial cells throughout the brain in accord with infarct topography and duration. These results emphasize the global yet temporally regulated nature of COX-2 induction during focal ischemia in humans, clearly different from the circumscribed acute expression reported in experimental animal models. We speculate that early induction of COX-2 may fuel tissue damage through prostanoids and free radicals, and delayed induction in remote brain areas may promote reconstitutive processes in the face of tissue scarring and remodeling of the surviving neural networks.