Perspectives in Diagnosis and Treatment of Rabies Viral Encephalitis: Insights from Pathogenesis.

Rabies viral encephalitis, though one of the oldest recognized infectious disease of humans, remains an incurable, fatal encephalomyelitis, despite advances in understanding of its pathobiology. Advances in science have led us on the trail of the virus in the host, but the sanctuaries in which the virus remains hidden for its survival are unknown. Insights into host-pathogen interactions have facilitated evolving immunologic therapeutic strategies, though we are far from a cure. Most of the present-day knowledge has evolved from in vitro studies using fixed (attenuated) laboratory strains that may not be applicable in the clinical setting. Much remains to be unraveled about this elusive virus. This review attempts to re-examine the current advances in understanding of the pathobiology of the rabies virus that modulate the diagnosis, treatment, and prevention of this fatal disease.

Role of apoptosis in rabies viral encephalitis: a comparative study in mice, canine, and human brain with a review of literature.

To evaluate the role of apoptosis in rabies encephalitis in humans and canines infected with wild-type street virus, in comparison with rodent model infected with street and laboratory passaged CVS strain, we studied postmortem brain tissue from nine humans, six canines infected with street rabies virus, and Swiss albino mice inoculated intramuscularly (IM) and intracerebrally (IC) with street and CVS strains. Encephalitis and high rabies antigen load were prominent in canine and human brains compared to rodents inoculated with street virus. Neuronal apoptosis was detectable only in sucking mice inoculated with CVS strain and minimal in street virus inoculated mice. In a time point study in suckling mice, DNA laddering was noted only terminally (7 days p.i.) following IC inoculation with CVS strain but not with street virus. In weanling and adult mice, apoptosis was restricted to inflammatory cells and absent in neurons similar to human and canine rabies-infected brains. Absence of neuronal apoptosis in wild-type rabies may facilitate intraneuronal survival and replication while apoptosis in inflammatory cells prevents elimination of the virus by abrogation of host inflammatory response.

Rabies viral encephalitis: clinical determinants in diagnosis with special reference to paralytic form.

BACKGROUND: Rabies is an important public health problem in developing countries such as India where an alarmingly high incidence of the infection is reported every year despite the availability of highly effective, potent and safe vaccines. In clinical practice, diagnosis of the furious (encephalitic) form of rabies poses little difficulty. In contrast, the paralytic form poses a diagnostic dilemma, to distinguish it from Guillain-Barré syndrome. The problem is further compounded in the absence of a history of dog bite, clinical features resembling a psychiatric syndrome. METHOD: The present study analysed the spectrum of neurological manifestations in 47 cases of rabies encephalitis (34 paralytic, six encephalitic, and seven psychiatric manifestations) from two hospitals in south India, confirmed at post-mortem by demonstration of a viral antigen in the brain. A history of dog bite was elicited in 33 patients and fox bite in one. Twenty-two patients received postexposure prophylaxis. The incubation period ranged from 7 days to 4 years. Clinical features were analysed, looking for any clinical pointers that provide clues to a diagnosis of paralytic rabies. RESULTS AND DISCUSSION: Fever, distal paresthaesias, fasciculation, alteration in sensorium, rapid progression of symptoms and pleocytosis in cerebrospinal fluid should alert the neurologist to consider rabies encephalomyelitis. Detection of the viral antigen in the corneal smear and a skin biopsy from the nape of the neck had limited usefulness in the ante-mortem diagnosis. Although a few clinical signs may help indicate rabies encephalomyelitis antemortem, confirmation requires neuropathological/neurovirological assistance. The preponderance of atypical/paralytic cases in this series suggests that neurologists and psychiatrists need to have a high index of clinical suspicion, particularly in the absence of a history of dog bite.

Papillary glioneuronal tumor-evidence of stem cell origin with biphenotypic differentiation.

Papillary glioneuronal tumors are newly recognized seizure producing tumors. We report two such cases with immunohistochemical characterization of glial and neuronal components and briefly review literature. Co-localization of glial and neuronal markers was demonstrable on confocal microscopy with expression of stem cell markers (Nestin and CD133) suggesting possible origin from neuroepithelial stem cell with biphenotypic differentiation.

Neuroanatomical mapping of rabies nucleocapsid viral antigen distribution and apoptosis in pathogenesis in street dog rabies--an immunohistochemical study.

AIM: To date, there is no study from Asian countries describing the pathology and topographic distribution of virulent, "street" rabies viral infection in the canine brain. In the present study, neuroanatomical distribution of rabies viral antigen in the brains of rabid street dogs, by immunohistochemical techniques is documented and the role of apoptosis in pathogenesis of rabies in natural hosts especially canines infected with street virus is studied. MATERIALS AND METHODS: 10 brains of adult street dogs from urban areas of Bangalore, South Central India, infected with rabies were collected. The diagnosis was confirmed by immunofluorescent study. The pathomorphological features and the neuroanatomic distribution of the viral antigen by immunohistochemistry were studied. The ability of the virus to activate apoptosis in nerve cells if any, was studied by determining the DNA fragmentation and TUNEL technique in infected canine brains. RESULTS: The viral antigen was mostly localized to the neuronal perikaryon extending along the dendrites, while occasional astrocytes were also labeled. In the brain, the limbic areas, thalamus and the reticular formation of the brain stem, the trigeminal and the vagal nuclei were involved, corresponding to areas of cholinergic innervation. It is proposed that the preferential involvement of these cholinergic zones could explain some of the clinical features of rabies in canines. The extensive involvement of thalamus and immunolocalization of the rabies viral antigen in the axons are the unusual features noted in a dog's brain in contrast to murine experimental studies with "fixed virus". Characteristic DNA fragmentation forming 180-200 bp, leading to laddering was not seen, indicating apoptosis is not involved in the evolution of lesions in rabies in adult dogs infected by street virus.

Rabies encephalitis following fox bite--histological and immunohistochemical evaluation of lesions caused by virus.

Rabies caused by fox bite is uncommon, most cases being caused by bite of rabid dogs (95%). We report a 45-year-old lady with rabies encephalomyelitis caused by bite of a rabid wild fox (Vulpes vulpes), a species prevalent in the Deccan plateaus of Central India. Though foxes are known to be susceptible to rabies, literature on the pathological changes caused by fox bite rabies in humans is scarce. Unlike the mild histological alterations described in canine rabies, a florid encephalitic process evolved in fox bite rabies, in our case, with intense microglial reaction, neuronophagia and perivascular inflammatory infiltrates despite clinical manifestation as a paralytic rabies. Immunostaining using polyclonal antibodies to the rabies viral nucleocapsid antigen and to the whole virion demonstrated high viral load within neurons with extensive spread along dendritic arborization and axonal tracts. Genomic sequence analysis demonstrated close homology with canine virus strain with only minor variations.

Simulated post-exposure rabies vaccination with purified chick embryo cell vaccine using a modified Thai Red Cross regimen.

OBJECTIVES: Currently, two intradermal regimens for the administration of cell culture rabies vaccines are approved by the WHO for rabies post-exposure prophylaxis: the two site Thai Red Cross regimen (TRC) and the eight site regimen. For the TRC regimen the volume of vaccine recommended per dose is 0.1 ml of purified Vero cell rabies vaccine (PVRV) and 0.2 ml of purified chick embryo cell vaccine (PCEC). The objective of the present study was to evaluate comparatively the immune response to PCEC and PVRV vaccines administered by the TRC regimen using a uniform dose of 0.1 ml of vaccine. METHODS: Forty-two subjects received TRC regimen (2-2-2-0-1-1) with 0.1 ml of PCEC vaccine and 38 subjects received the same regimen with PVRV. The rabies neutralizing antibody response in these subjects on days 10, 28, 90 and 180 was determined by the standard mouse neutralization test (MNT). RESULTS: There was adequate antibody response with both the vaccines and 100% seroconversion was observed by day 10. Furthermore, the antibody titers obtained with PCEC did not differ significantly from those obtained with PVRV on all days tested (p > 0.05). CONCLUSIONS: It can be concluded from the results that an adequate antibody response can be obtained with PCEC vaccine when administered by the TRC regimen even after reducing the quantity of vaccine from 0.2 ml to 0.1 ml per intradermal dose. The feasibility of using this regimen in true post-exposure cases needs to be further evaluated.

Development and evaluation of an enzyme immunoassay for rapid diagnosis of rabies in humans and animals.

The presently advocated tests for rapid diagnosis of rabies such as fluorescent antibody test (FAT) is expensive and requires expertise to carry out and interpret the results. In this study we have developed and evaluated a simple enzyme immuno-assay (EIA) to detect rabies antigen in the brain specimens of animals and humans. We have also evaluated the utility of this test in ante mortem diagnosis of human rabies. The brain homogenates of suspected rabid animals (n=250), humans (n=16) and clinical samples like saliva (n=16) and cerebrospinal fluid (CSF, n=16) applied on to ELISA plates coated with rabies antinucleoprotein antibody and the absorbed rabies nucleoprotein antigen was detected using biotinylated anti-nucleoprotein antibody followed by treatment with streptavidin peroxidase conjugate and colour development with OPD. Rabies infected and normal mouse brain homogenates were used as positive and negative controls respectively. The results of this test was evaluated with fluorescent antibody technique (for brain samples) and mice inoculation test (for saliva and CSF samples). A distinct dark brown color was seen in positive control and all positive samples and there was no color development in negative control and samples. The concordance between FAT and EIA was 98.4%. With brain samples, 83.3% with saliva and 91.6% with CSF samples. The specificity of the test was found to be 100%. It can be concluded that the EIA described here is a sensitive, specific and rapid test for post mortem diagnosis of rabies in animals and humans. The utility of this test for ante mortem diagnosis of rabies needs to be further evaluated.