Japanese encephalitis — DTM&H MCQ

Correct answer: C — Japanese encephalitis

Explanation lettering: E = shown as A · C = shown as B · A = shown as C · B = shown as D · D = shown as E

Japanese encephalitis (A) is the most likely diagnosis because the vignette combines a child in rural Southeast Asia during rice-growing season with fever, seizures and reduced consciousness, the classic epidemiological and clinical picture of JE virus infection. Japanese encephalitis virus is transmitted by Culex mosquitoes that breed prolifically in flooded rice paddies, with pigs and wading birds acting as amplifying hosts, so incidence peaks with the agricultural cycle in endemic rural Asia. Children are disproportionately affected because adults in endemic areas usually have acquired immunity, and the exclusion of malaria parasitaemia removes the main alternative cause of febrile encephalopathy in this setting. The seizure burden and rapid progression to reduced consciousness are typical of JE, which remains the leading cause of viral encephalitis in Asia. Why the other options are wrong: B. Dengue encephalopathy: dengue more typically causes fever with rash, myalgia, thrombocytopenia and haemorrhagic manifestations, with encephalopathy being a rare complication rather than the classic presentation, and it lacks the specific rice paddy and seasonal vector link. C. Cerebral malaria: explicitly excluded by the stem stating no malaria parasitaemia, which removes this as a viable diagnosis regardless of clinical similarity. D. Rabies: rabies causes a progressive encephalitic or paralytic illness usually following an animal bite with hydrophobia and autonomic hyperactivity, not an acute febrile seizure illness tied to rice-growing season and mosquito exposure. E. Nipah virus infection: Nipah is linked to fruit bat and pig exposure in outbreak settings, mainly in Malaysia, Bangladesh and India, and is far less common than JE in rural Vietnam without a specific outbreak context. Key point: fever with seizures and reduced consciousness in a rural Southeast Asian child during rice-growing season, with malaria excluded, points to Japanese encephalitis via its Culex mosquito and rice paddy transmission cycle.

Reference: NaTHNaC (TravelHealthPro), Japanese Encephalitis factsheet, https://travelhealthpro.org.uk/factsheet/55/japanese-encephalitis