Immunohistochemical and histopathological study of experimental rabies infection in mice

Combination drug treatment prolongs survival of experimentally infected mice with silver-haired bat rabies virus

Rabies is a lethal disease in humans and animals, killing approximately 60,000 people every year. Currently, there is no treatment available, except post-exposure prophylaxis (PEP) that can be administered whenever exposure to a rabid animal took place. Here we describe the beneficial effects of a combination treatment initiated at day 4 post infection, containing anti-viral drugs and immune modulators in infected mice. Combination therapy resulted in significant increase in survival time (P < 0.05) and significantly lowers viral RNA in the brain and spinal cord (P < 0.05). Furthermore, treatment influenced markers of pyroptosis and apoptosis and early inflammatory response as measured by the levels of TNF-α. Morphological lesions were absent in rabies virus infected mice with few signs of inflammation. However, these were not significant between the different groups.

Comparative analysis of European bat lyssavirus 1 pathogenicity in the mouse model

European bat lyssavirus 1 is responsible for most bat rabies cases in Europe. Although EBLV-1 isolates display a high degree of sequence identity, different sublineages exist. In individual isolates various insertions and deletions have been identified, with unknown impact on viral replication and pathogenicity. In order to assess whether different genetic features of EBLV-1 isolates correlate with phenotypic changes, different EBLV-1 variants were compared for pathogenicity in the mouse model. Groups of three mice were infected intracranially (i.c.) with 102 TCID50/ml and groups of six mice were infected intramuscularly (i.m.) with 105 TCID50/ml and 102 TCID50/ml as well as intranasally (i.n.) with 102 TCID50/ml. Significant differences in survival following i.m. inoculation with low doses as well as i.n. inoculation were observed. Also, striking variations in incubation periods following i.c. inoculation and i.m. inoculation with high doses were seen. Hereby, the clinical picture differed between general symptoms, spasms and aggressiveness depending on the inoculation route. Immunohistochemistry of mouse brains showed that the virus distribution in the brain depended on the inoculation route. In conclusion, different EBLV-1 isolates differ in pathogenicity indicating variation which is not reflected in studies of single isolates.

A non-invasive intranasal inoculation technique using isoflurane anesthesia to infect the brain of mice with rabies virus

Methods for intranasal inoculation of viruses are often described poorly and the effects of variations in the technique on the outcome are unknown. Standardization of protocols is key to compare studies and minimize animal use. The clinical and virological outcome of infection with rabies virus (genotypes 1 and 5) upon administration of different inoculum volumes (25, 50 and 100μl) and different anesthetic regimens were examined. Administration of 25μl of virus as a drop on both nostrils under brief superficial isoflurane anesthesia (92μl/dm(3), recovery after 85 ± 1 0s) was the most effective to infect the brain and induced 100% lethal infection 9 days later. Increasing the inoculum volume reduced infectivity significantly, with decreased viral loads in the brain and only 40% mortality. Increasing the depth of isoflurane anesthesia (230μl/dm(3)) improved the infectivity of the large-volume inoculum (90% mortality), probably because of suppression of swallow and sneeze reflexes. Compared to isoflurane anesthesia, xylazine-ketamine anesthesia reduced the infectivity of the inoculum significantly. Thus, administration of a small volume of virus on the nostrils under brief gas anesthesia is a safe and reproducible technique to induce infection of the brain. Since needles are not required, this helps to preserve the integrity of the physical barriers, animal welfare and the manipulator's safety.

Acute canine distemper encephalitis is associated with rapid neuronal loss and local immune activation

For most virus infections of the central nervous system (CNS), immune-mediated damage, the route of inoculation and death of infected cells all contribute to the pathology observed. To investigate the role of these factors in early canine distemper neuropathogenesis, we infected ferrets either intranasally or intraperitoneally with the neurovirulent canine distemper virus strain Snyder Hill. Regardless of the route of inoculation, the virus primarily targeted the olfactory bulb, brainstem, hippocampus and cerebellum, whereas only occasional foci were detected in the cortex. The infection led to widespread neuronal loss, which correlated with the clinical signs observed. Increased numbers of activated microglia, reactive gliosis and different pro-inflammatory cytokines were detected in the infected areas, suggesting that the presence and ultimate death of infected cells at early times after infection trigger strong local immune activation, despite the observed systemic immunosuppression.

Comparative pathological study of the murine brain after experimental infection with classical rabies virus and European bat lyssaviruses

European bat lyssaviruses (EBLVs) types 1 (EBLV-1) and 2 (EBLV-2) cause rabies in terrestrial species, but the pathological changes associated with neuroinvasion have yet to be fully elucidated. Swiss OF-1 mice were inoculated peripherally with strain RV61 (classical rabies virus), RV1423 (EBLV-1) or RV1332 (EBLV-2) to compare the nature and extent of histopathological changes produced. Inoculated animals developed varying degrees of non-suppurative encephalitis, and lyssavirus infection was confirmed by the detection of viral antigen. The lesions produced, which included perivascular cuffs and gliosis, were more severe after RV1423 or RV1332 infection than after RV61 infection. Perivascular cuffs were mainly localized to caudal brain regions, irrespective of the infecting strain; after RV1332 infection, however, they were particularly abundant, being composed of large numbers of inflammatory cells. T cells were the predominant lymphocytic component of the inflammatory infiltrate in both the Virchow-Robin space and the brain parenchyma. Viral antigen, which was widespread throughout the brain, was apparently unrelated to the degree of cuffing. The study suggested that there was increased immune activation after inoculation with strain RV1423 or RV1332, particularly the latter, but that this did not affect the final outcome.

Detection of rabies viral antigens in non-autolysed and autolysed tissues by using an immunoperoxidase technique

The objectives of this study were to determine the potential of an immunoperoxidase technique involving the avidin-biotin complex (ABC) stain for the diagnosis of rabies in fresh tissues and compare it with other standard methods, including the fluorescent antibody test (FAT), haematoxylin and eosin and Seller's stain, and to investigate its capacity to detect rabies antigen in autolysed tissues. Samples of non-autolysed brain from 81 domestic and wild animals suspected of having rabies were examined. Rabies antigen was detected by FAT in 41 of these samples and Negri bodies were detected in 40 (97.6 per cent) of them by the immunoperoxidase technique, in 25 by haematoxylin and eosin and in 22 by Seller's stain. The sensitivity of the immunoperoxidase technique decreased as the tissues were left to autolyse; after two days it was 91.2 per cent, after four days 70.6 per cent, and after seven days 11.8 per cent.

[Advances in rabies research]

Recent advances in research into rabies, based on the technological process of the biological sciences mainly molecular biology and genetic engineering, are mentioned. The current knowledge of the characteristics, properties pathogeny and immunology of the rabies views is presented, as well as the development of new diagnostic and vaccine evaluation techniques. The epidemiological importance of the identification of different immunogenic rabies virus strains and the role in immunoprophylaxis of the production of highly immunogenic vaccines, are set out.