Abstract
Rabies is a zoonotic disease that affects many mammals, including humans, through bites from infected animals. We report a necropsy of rabies in a male patient from a rural background and the vital role of forensic histopathology in confirming the diagnosis of rabies. A man was admitted with fever, altered sensorium, aggressive behaviour and unconsciousness. Two years earlier he had been scratched on the foot by a stray dog but had received no anti-rabies treatment. He died within 96 hours of symptom onset. Histopathological testing of the brain during necropsy showed the presence of Negri bodies and confirmed the diagnosis of rabies. Although the incubation period of rabies can vary widely, this was not a classic case of rabies infection with a normal incubation period. In rural settings, where molecular testing is difficult, appropriate testing and analysis of samples with histopathology can clarify the diagnosis.
Rabies is a severe, untreatable and advancing viral brain inflammation caused by viruses belonging to the Rhabdoviridae family and Lyssavirus genus. 1 Except for Antarctica and a few islands, this virus has spread to more than 150 countries, with most victims living in rural communities in Asia and Africa. 2 In India, rabies is endemic in all states and union territories except the Andaman and Nicobar Islands and Lakshadweep, with 6644 deaths reported from 2012 to 2022. 3
Social costs encompass fatalities, reduced productivity due to premature death, illnesses caused by vaccination side effects and mental strain faced by individuals when exposed to these lethal diseases. 4
Species such as dogs, monkeys, cats, wolves, goats, rabbits, horses and cows are susceptible to rabies infection. 5 However, most humans contract the rabies virus by bites or scratches from domesticated dogs.
Prompt administration of post-exposure prophylaxis (PEP) is one of the key strategies to prevent rabies-related deaths in humans. Delaying PEP or not completing the prescribed doses can lead to the development of clinical rabies and death. 6
Case report
A 48-year-old male patient, a worker, presented at a tertiary care hospital in central India with complaints of sudden onset of altered sensorium with behavioural changes, restlessness and agitation. On examination, he had a high-grade fever for the past 3 days, frothing from the mouth, and inability to eat and drink normally.
The patient had a history of a dog paw scratch 2 years earlier. The dog was raised as a non-vaccinated pet by the victim’s neighbours. No similar complaints were observed in other family members or neighbours. Despite local awareness campaigns on rabies and PEP, the patient did not seek medical attention because of the lack of immediate symptoms and socioeconomic barriers.
Initially, the power in all four limbs was normal. The pupils were bilaterally responsive to light, with no neck rigidity or photophobia. This rapidly progressed to hydrophobia, photophobia, neck rigidity and depressed bilateral plantar flexor reflexes, raising the suspicion of rabies. The patient died on the day of admission at approximately 11.40 PM, and 3 days after the onset of symptoms. The body was sent for a detailed post-mortem examination.
Post-mortem findings
Post-mortem examination revealed rigor mortis all over the body and purple post-mortem lividity over the back. No signs of defensive injury or external evidence of foul play were observed. On internal examination, the brain was severely congested and oedematous, no gross abnormalities were visible and other organs were congested. Glottis oedema present with trachea shows congested mucosa. The brain was dissected from the cranial cavity and fixed in 40% formalin by suspending it with ligation through the basilar artery.
Neuro-histopathological findings
On gross inspection, the whole brain weighed 1225 g. Externally, both hemispheres showed normal gyri and sulci. Eleven blocks were used to investigate the histological realm.
On microscopic examination, representative blocks taken from the cerebrum and cerebellum showed the molecular and granular layers with many Purkinje cells showing cytoplasmic, round and oval eosinophilic globular deposits, that is, Negri bodies. Another finding was mild oedema with mild perivascular lymphocytic infiltration. Blocks taken from other brain regions were unremarkable or showed mild oedema.
Microscopic examination of the kidney showed acute tubular necrosis; the spleen had congested red pulp with compressed white pulp and sickled red RBCs in sinusoids, and the right coronary artery showed mild fibrointimal hyperplasia. The remaining samples from the other organs showed normal histology. Histopathological analysis of cerebellar tissue displaying Negri bodies in a case of rabies encephalitis (H&E staining, various magnifications), as shown in Figure 1.
Shows histopathological analysis of cerebellar tissue displaying Negri bodies in a case of rabies encephalitis (H&E staining, various magnifications). The arrow shows Negri Bodies.
Surrounding the infected neurons, there is notable neuropil vacuolisation and neuronal degeneration, accompanied by perivascular cuffing and microglial proliferation, consistent with viral encephalitis. The background parenchyma exhibited varying degrees of spongiform changes and glial reactivity.
Discussion
Epidemiology and challenges in India
Rabies remains a neglected disease in India, despite its preventable nature. In this case, the absence of PEP following a dog scratch was a critical factor that led to the patient’s death. Arora et al. presented a case of corneal donation in which ROTA was averted because of a high index of suspicion for rabies in the donor. The corneas were subjected to a fluorescent antibody test (FAT), and rabies virus antigen was detected. 7
Pathophysiology of rabies
Following inoculation through a bite, the rabies virus binds to nicotinic acetylcholine receptors and travels retrogradely along the peripheral nerves to the CNS. 8 The incubation period depends on the distance from the bite site to the brain but typically lasts 1–3 months, based on how close the bite is to the CNS and the amount of virus present. The patient’s incubation period of 2 years in this particular case is very unusual. The incubation period may vary depending on the exposure site, rabies virus type, viral load and any existing immunity. 9
Upon entry into the central nervous system (CNS), the virus precipitates encephalitis, and as the infection progresses, the individual experiences heightened CNS excitability. Even minimal tactile stimuli can cause pain, eliciting intense motor responses and convulsions. Contraction of the pharyngeal muscles during swallowing results in the production of oral froth, potentially leading to an aversion to swallowing, clinically manifesting as hydrophobia. Although hydrophobia is highly indicative, none of the clinical signs are definitive for diagnosing rabies. 10
Specific diagnosis in the early stages of rabies in live patients is difficult and unnoticed because other viral encephalitis symptoms are often overlooked. The diagnosis of rabies infection in living people is difficult. 11 Radiological investigations have proven beneficial to a certain extent. In cases of rabies, MRI scans predominantly reveal involvement of the grey matter, specifically affecting the basal ganglia, thalami, pontine and midbrain nuclei. 12 In two instances, various laboratory tests for diagnosing rabies, including the fluorescent antibody test, enzyme-linked immunosorbent assay (ELISA) and mouse inoculation test, were performed. 12 Rabies can be diagnosed in vivo or posthumously. 13 The identification of Negri bodies in brain tissue during autopsy is the most definitive and specific pathological finding. 14
Role of histopathology and laboratory tests
Histopathological identification of Negri bodies remains a cornerstone of rabies diagnosis in forensic settings. Additionally, confirmatory tests such as DFA and RT-PCR enhance diagnostic accuracy. Post-mortem analysis of cerebrospinal fluid using real-time PCR testing verified the presence of rabies in some cases. The author reported a diagnosis of rabies in an 11-year-old child with a history of dog bites to her/his leg 5 years earlier. 2
The brain and spinal cord exhibited widespread softening, and the spinal subarachnoid space was enlarged owing to the presence of purulent exudate. Peripheral nerves showed extensive axonal degeneration, characterised by the loss of both myelinated and unmyelinated fibres, along with significant mononuclear infiltrates throughout the nerve and occasional multinucleate giant cells. Similar alterations were observed in the dorsal root ganglia. 15
Medico-legal implications
The cost-effectiveness of pre-exposure prophylaxis for children in high-risk areas, such as this tribal settlement, should be evaluated and compared with the WHO-recommended strategies of mass canine vaccination and health. 16
Conclusion
Autopsy cases of rabies infection are scarce in the literature, with a focus on clinical presentation and viral antigen detection in select neuropathology centres. The current report emphasises autopsy practices and histological confirmation of rabies viral encephalitis, along with forensic and medico-legal aspects. This study focuses on the need to raise awareness regarding post-exposure prophylaxis and general awareness of the disease.
Autopsy findings and histological confirmation are key to establishing a rabies diagnosis.
Footnotes
Acknowledgements
We thank all the staff of the Department of Pathology who contributed to the neurohistopathology of this report.
Author contributions
All authors have contributed to this manuscript in terms of planning, conception and design; writing and editing various drafts of the manuscript and reading and approving the final version of the manuscript.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Informed consent
Informed consent taken from next of kin.
