Paper II — 2021 February (Supplementary) (2010 Scheme) — Q1
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Paper II
2021 February (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
A 20 years old male patient was admitted in hospital with the complaints of difficulty in
swallowing liquids, loss of appetite and restlessness. He gave history of dog bite by
a street dog one month back.
What is the diagnosis of this condition
Discuss the pathogenesis
Describe the laboratory diagnosis of the condition
What are the post exposure prophylactic measures of this condition (1+3+3+3)
Q110 marksEssays
Answer
Diagnosis: Rabies (furious/encephalitic form) — hydrophobia (difficulty/fear of swallowing liquids), restlessness, and a history of dog bite by a street dog one month earlier is classical.
Pathogenesis
Rabies virus (a rhabdovirus) is introduced into a bite wound in the saliva of an infected animal; it first replicates locally in muscle tissue near the inoculation site, then enters peripheral nerve endings and travels retrograde along axons toward the CNS — the incubation period (here, about a month) depends largely on the distance from the bite site to the CNS and the viral inoculum. Once in the CNS, the virus replicates extensively in neurons (producing Negri bodies, classically in hippocampal/Purkinje cells), causing severe encephalitis. From the CNS, the virus spreads centrifugally via peripheral nerves to other tissues, notably the salivary glands (basis for further transmission) and other highly innervated tissues. The hydrophobia characteristic of furious rabies results from painful, violent pharyngeal/laryngeal muscle spasm triggered by attempts to swallow, related to brainstem involvement and autonomic dysregulation.
Laboratory diagnosis
Direct Fluorescent Antibody (DFA) test — gold-standard confirmatory test, on brain tissue (post-mortem) or, antemortem, nuchal skin biopsy, corneal impression smear, or saliva.
Negri body demonstration — classical histopathological finding, though absence does not exclude rabies.
RT-PCR — highly sensitive molecular detection of viral RNA in saliva, CSF, or tissue.
Serology — detection of rabies-neutralizing antibody, useful in unvaccinated patients surviving long enough to mount a response.
Post-exposure prophylactic measures
Wound management: immediate, thorough washing with soap and water for at least 15 minutes, followed by a virucidal agent; suturing avoided/delayed.
Category-based management: Category II (minor scratches) — vaccine alone; Category III (transdermal bites, deep scratches, mucous membrane exposure — applicable here given a definite bite wound) — vaccine PLUS Rabies Immunoglobulin (RIG), infiltrated around the wound.
Active immunization: modern cell-culture-derived vaccines (HDCV, PCECV, PVRV) on a defined multi-dose schedule (e.g., days 0, 3, 7, 14, ± 28).
Passive immunization: RIG for Category III exposures, providing immediate neutralizing antibody while active immunity develops.
Note: since this patient is already symptomatic (established clinical rabies), post-exposure prophylaxis at this stage would not alter the outcome — treatment is now purely palliative/supportive; the prophylactic measures described are those that should have been (and should generally be) instituted promptly after the bite, before symptom onset.
