Which part of human body is infected by the virus causing Japanese encephalitis?

Correct — option (3), Brain.

Encephalitis is inflammation of the brain. The US Centers for Disease Control and Prevention (CDC) says that most people infected with Japanese encephalitis (JE) virus have no symptoms or only mild ones, but a small percentage develop inflammation of the brain (encephalitis).

WHO's JE fact sheet (9 May 2019) calls the virus the main cause of viral encephalitis in many countries of Asia. The severe illness it describes is neurological: high fever, headache, neck stiffness, disorientation, coma, seizures and spastic paralysis.

So the part of the body the JE virus attacks in serious cases is the brain.

The idea to remember: encephalitis = inflamed brain; JE is a mosquito-borne viral encephalitis.

Why the others are wrong

• (1)
  Skin — The skin is only the entry point. WHO says JE virus reaches humans through bites from infected Culex mosquitoes, so the virus crosses the skin at the bite.

  The disease itself is encephalitis. The warning signs WHO and CDC list, such as disorientation, seizures and coma, come from the brain, not from the skin.

• (2)
  Red blood cells — Red blood cells are what the malaria parasite attacks. NCERT says Plasmodium multiplies in liver cells and then attacks red blood cells, rupturing them.

  JE is caused by a virus, not a protozoan. WHO describes JE virus as a flavivirus whose severe form is encephalitis; humans, once infected, do not even develop enough virus in the blood to infect feeding mosquitoes.

• (4)
  Lungs — Lung disease belongs to respiratory infections such as SARS, which WHO describes as a viral respiratory disease caused by a SARS-associated coronavirus.

  The severe signs WHO lists for JE are neurological: neck stiffness, disorientation, coma, seizures and spastic paralysis. WHO even prefers testing cerebrospinal fluid, the fluid around the brain and spinal cord, to confirm JE.

Japanese encephalitis is caused by JE virus, which WHO describes as a flavivirus related to dengue, yellow fever and West Nile viruses.

The virus circulates between mosquitoes and pigs and/or water birds. Humans are infected through bites of Culex mosquitoes, mainly Culex tritaeniorhynchus.

WHO says most infections are mild, with fever and headache, or have no apparent symptoms, and about 1 in 250 results in severe clinical illness. CDC describes the serious form as inflammation of the brain (encephalitis).

Key facts

• CDC: a small percentage of people infected with JE virus develop inflammation of the brain (encephalitis).
• WHO (9 May 2019): JE virus is a mosquito-borne flavivirus, related to dengue, yellow fever and West Nile viruses.
• WHO: humans are infected through bites of Culex mosquitoes, mainly Culex tritaeniorhynchus; the virus cycles between mosquitoes, pigs and/or water birds.
• WHO: about 1 in 250 JE virus infections results in severe clinical illness; the case-fatality rate among those with disease symptoms can be as high as 30%.
• WHO: the first case of JE was documented in 1871 in Japan; there is no antiviral treatment, but vaccines are available.

Common traps

• Entry point versus target: the virus enters through a mosquito bite in the skin, but the disease is in the brain.
• Mosquito-borne does not mean a blood-cell disease: malaria's Plasmodium attacks red blood cells, while JE virus inflames the brain.
• The name says 'Japanese', but WHO counts 24 countries with endemic transmission across South-East Asia and the Western Pacific; the first documented case was in Japan in 1871.

• practice — not a real PYQ

  Japanese encephalitis virus is transmitted to humans mainly through the bite of –

  • (a)Female Anopheles mosquito
  • (b)Housefly
  • (c)Culex tritaeniorhynchus mosquito
  • (d)Rat flea
  Answer(3) — WHO says JE virus reaches humans through bites of infected Culex mosquitoes, mainly Culex tritaeniorhynchus. Option (1) is the vector NCERT names for malaria, and WHO names neither option (2) nor option (4) as a JE vector.
• practice — not a real PYQ

  According to WHO, humans infected with Japanese encephalitis virus do not pass it on to feeding mosquitoes because –

  • (a)they do not develop enough virus in the blood
  • (b)the virus is destroyed in the skin
  • (c)Culex mosquitoes do not bite humans
  • (d)the virus stays only in the lungs
  Answer(1) — WHO says humans, once infected, do not develop sufficient viraemia to infect feeding mosquitoes. Option (3) contradicts WHO, which says humans are infected by Culex bites, and options (2) and (4) contradict the disease's course to the brain.