Questions

Japanese encephalitis virus — Questions

Study questions about Japanese encephalitis virus — exam-style, clinical-scenario and FAQ.

Mock Exam mode

Sit this set one question at a time. Multiple-choice questions mark themselves; written questions reveal a tickable mark scheme so you can score your own answer. You get a combined score at the end.

11 questions: 11 MCQ, 0 written.

With a very high ratio of subclinical to clinical infection (on the order of 250 to 1), most people in endemic areas are infected and immune by adulthood, so clinical disease falls mainly on children.

The other groups are not the predominant affected population in highly endemic settings.

The vaccine is recommended for longer or rural stays in endemic Asia during the transmission season, where the mosquito vector breeds in flooded rice fields and pigs amplify the virus.

Brief urban trips carry negligible risk, and the other destinations lie outside the endemic range of the virus.

Japanese encephalitis virus is the prototype of the Japanese encephalitis serocomplex, which also contains West Nile, St Louis encephalitis and Murray Valley encephalitis viruses, and shares their neurotropism.

Dengue, Spondweni (which holds Zika), tick-borne encephalitis and yellow fever form separate serogroups.

Japanese encephalitis virus has a predilection for the deep grey matter, especially the substantia nigra and basal ganglia, producing extrapyramidal features and a Parkinson-like syndrome that often appears in convalescence.

The cerebellum, occipital cortex, hippocampus and pituitary are not the characteristic targets.

Culex tritaeniorhynchus, which breeds in rice paddies and other ground pools, is the principal vector, linking the disease to irrigated rice agriculture across Asia.

Tree-hole and container-breeding Aedes transmit yellow fever, dengue and Zika, not Japanese encephalitis.

IgM-capture ELISA on serum and cerebrospinal fluid is the standard test, with sensitivity approaching 100% when both are tested one to two weeks after onset; cerebrospinal-fluid IgM indicates central nervous system infection. Flavivirus cross-reactivity is the main limitation.

Virus is rarely isolated, blood is cleared early, and electroencephalography and biopsy are not confirmatory.

Pigs are the key amplifying host, developing a high viraemia and living close to people in rural Asia, while ardeid wading birds are natural maintenance hosts; humans and horses are dead-end hosts.

Primates, rodents and bats are not the amplifying hosts for Japanese encephalitis.

Ardeid wading birds, such as herons and egrets, are the natural maintenance hosts, with pigs as the amplifying host that drives human exposure.

Poultry, songbirds and waterfowl are not the recognised maintenance hosts, and birds are integral to the cycle.

Bilateral thalamic lesions are characteristic of Japanese encephalitis on CT or MRI, in keeping with its deep grey-matter tropism.

Temporal-lobe necrosis suggests herpes simplex encephalitis, and the other patterns are not typical of Japanese encephalitis.

Effective inactivated (for example the Vero-cell IXIARO) and live-attenuated (SA14-14-2) vaccines drive routine childhood immunisation across endemic Asia and are recommended for at-risk travellers; because the virus is a single serotype, they protect across genotypes.

The mouse-brain vaccine is largely phased out, vaccines are not genotype-restricted, and children are the main target group.

Human viraemia is too low to infect feeding mosquitoes, so people cannot sustain the cycle, which is maintained by pigs and wading birds; there is no human-to-human spread.

Humans are fully susceptible and are bitten in the field, so the other options are incorrect.

MCQ
In highly endemic areas of Asia, clinical Japanese encephalitis falls mainly on which group, and why?
- A. The elderly, because of waning vaccine immunity
- B. Pregnant women, because of immune tolerance
- C. Travellers, because they lack any exposure
- D. Male farm workers, because of occupational bites
- E. Children, because most adults are already immune
Show answer
Correct answer: E
With a very high ratio of subclinical to clinical infection (on the order of 250 to 1), most people in endemic areas are infected and immune by adulthood, so clinical disease falls mainly on children.

The other groups are not the predominant affected population in highly endemic settings.
MCQ
Japanese encephalitis vaccine is most clearly indicated for a traveller who is:
- A. A three-day urban business trip staying in central Tokyo
- B. A month in rural rice-farming Asia in the wet season
- C. A short beach holiday on the Brazilian coast
- D. Summer trekking in forests of the Baltic states
- E. A guided river cruise along the Egyptian Nile
Show answer
Correct answer: B
The vaccine is recommended for longer or rural stays in endemic Asia during the transmission season, where the mosquito vector breeds in flooded rice fields and pigs amplify the virus.

Brief urban trips carry negligible risk, and the other destinations lie outside the endemic range of the virus.
MCQ
Japanese encephalitis virus is the prototype of which serocomplex?
- A. The Japanese encephalitis serocomplex
- B. The dengue serocomplex
- C. The Spondweni group
- D. The tick-borne encephalitis serocomplex
- E. The yellow fever group
Show answer
Correct answer: A
Japanese encephalitis virus is the prototype of the Japanese encephalitis serocomplex, which also contains West Nile, St Louis encephalitis and Murray Valley encephalitis viruses, and shares their neurotropism.

Dengue, Spondweni (which holds Zika), tick-borne encephalitis and yellow fever form separate serogroups.
MCQ
The Parkinson-like movement disorder of Japanese encephalitis reflects a viral predilection for which brain region?
- A. The substantia nigra and basal ganglia
- B. The cerebellar vermis
- C. The occipital cortex
- D. The hippocampus
- E. The anterior pituitary
Show answer
Correct answer: A
Japanese encephalitis virus has a predilection for the deep grey matter, especially the substantia nigra and basal ganglia, producing extrapyramidal features and a Parkinson-like syndrome that often appears in convalescence.

The cerebellum, occipital cortex, hippocampus and pituitary are not the characteristic targets.
MCQ
The principal vector of Japanese encephalitis virus is a mosquito that breeds chiefly in:
- A. Tree holes in forest canopy
- B. Rice paddies and ground pools (Culex tritaeniorhynchus)
- C. Domestic water containers (Aedes aegypti)
- D. Brackish coastal marsh
- E. Rodent burrows
Show answer
Correct answer: B
Culex tritaeniorhynchus, which breeds in rice paddies and other ground pools, is the principal vector, linking the disease to irrigated rice agriculture across Asia.

Tree-hole and container-breeding Aedes transmit yellow fever, dengue and Zika, not Japanese encephalitis.
MCQ
The standard laboratory test for confirming Japanese encephalitis is:
- A. Blood culture for the virus
- B. Nucleic-acid testing of blood after two weeks
- C. IgM-capture ELISA on serum and cerebrospinal fluid
- D. Electroencephalography
- E. Brain biopsy
Show answer
Correct answer: C
IgM-capture ELISA on serum and cerebrospinal fluid is the standard test, with sensitivity approaching 100% when both are tested one to two weeks after onset; cerebrospinal-fluid IgM indicates central nervous system infection. Flavivirus cross-reactivity is the main limitation.

Virus is rarely isolated, blood is cleared early, and electroencephalography and biopsy are not confirmatory.
MCQ
Which animal is the key amplifying host in the Japanese encephalitis transmission cycle?
- A. Wild non-human primates
- B. Horses
- C. Pigs
- D. Rodents
- E. Bats
Show answer
Correct answer: C
Pigs are the key amplifying host, developing a high viraemia and living close to people in rural Asia, while ardeid wading birds are natural maintenance hosts; humans and horses are dead-end hosts.

Primates, rodents and bats are not the amplifying hosts for Japanese encephalitis.
MCQ
Which birds act as natural maintenance hosts for Japanese encephalitis virus?
- A. Domestic poultry
- B. Passerine songbirds
- C. Migratory waterfowl only
- D. Ardeid wading birds such as herons and egrets
- E. Birds play no part in the cycle
Show answer
Correct answer: D
Ardeid wading birds, such as herons and egrets, are the natural maintenance hosts, with pigs as the amplifying host that drives human exposure.

Poultry, songbirds and waterfowl are not the recognised maintenance hosts, and birds are integral to the cycle.
MCQ
Which neuroimaging finding is characteristic of Japanese encephalitis?
- A. Temporal lobe haemorrhagic necrosis
- B. Bilateral thalamic lesions
- C. Periventricular calcification
- D. Cerebellar atrophy
- E. A normal scan in all cases
Show answer
Correct answer: B
Bilateral thalamic lesions are characteristic of Japanese encephalitis on CT or MRI, in keeping with its deep grey-matter tropism.

Temporal-lobe necrosis suggests herpes simplex encephalitis, and the other patterns are not typical of Japanese encephalitis.
MCQ
Which statement about Japanese encephalitis vaccination is correct?
- A. No vaccine exists
- B. Only a mouse-brain vaccine is available
- C. Vaccines protect against a single genotype only
- D. Effective inactivated and live-attenuated vaccines underpin routine childhood immunisation in endemic Asia
- E. Vaccination is contraindicated in children
Show answer
Correct answer: D
Effective inactivated (for example the Vero-cell IXIARO) and live-attenuated (SA14-14-2) vaccines drive routine childhood immunisation across endemic Asia and are recommended for at-risk travellers; because the virus is a single serotype, they protect across genotypes.

The mouse-brain vaccine is largely phased out, vaccines are not genotype-restricted, and children are the main target group.
MCQ
Why are humans considered dead-end hosts for Japanese encephalitis virus?
- A. They are resistant to infection
- B. They are rarely bitten by Culex mosquitoes
- C. They transmit only to pigs
- D. They are infected only in the laboratory
- E. They do not develop enough viraemia to infect feeding mosquitoes
Show answer
Correct answer: E
Human viraemia is too low to infect feeding mosquitoes, so people cannot sustain the cycle, which is maintained by pigs and wading birds; there is no human-to-human spread.

Humans are fully susceptible and are bitten in the field, so the other options are incorrect.