Rabies encephalitis — DTM&H MCQ

Correct answer: A — Rabies

B) Rabies is correct because the vignette describes classic furious rabies encephalitis following an untreated dog bite in an endemic country. The incubation period of typically three to twelve weeks fits the two month interval, and the combination of fever, agitation and painful spasms triggered by attempts to drink (hydrophobia) is pathognomonic for rabies rather than any other CNS infection. The Philippines is a rabies endemic country where dog bites are the principal transmission route, and failure to give post exposure prophylaxis after such a bite leaves the patient unprotected once the virus reaches the CNS. Once furious rabies symptoms such as hydrophobia and hallucinations appear, the disease is essentially always fatal, distinguishing it clinically from other encephalitides that lack this specific water aversion phenomenon. Why the other options are wrong: E. Herpes simplex encephalitis: presents with fever, headache, seizures and focal neurological signs or personality change, but has no link to animal bites and does not cause hydrophobia or painful spasms provoked by water. C. Tetanus: causes painful muscle spasms and trismus from Clostridium tetani neurotoxin entering through a wound, but the incubation is typically days to a few weeks, not two months, and hydrophobia specifically triggered by the sight or attempt of drinking is not a tetanus feature. D. Cerebral malaria: causes fever and altered consciousness or seizures in a traveller to an endemic area, but has no relationship to a dog bite and does not produce hydrophobia or spasms on offering water. B. Japanese encephalitis: is mosquito borne, causes fever and encephalopathy, but is unrelated to dog bites and does not cause the specific hydrophobic spasms described. Key point: Hydrophobia (painful pharyngeal and laryngeal spasm triggered by attempting to drink) after an untreated animal bite in an endemic country is pathognomonic for furious rabies.

Reference: UK Health Security Agency (UKHSA), Immunisation against infectious disease (the Green Book), Chapter 27: Rabies, updated May 2023, https://www.gov.uk/government/publications/rabies-the-green-book-chapter-27