Water Sanitation Health

Japanese encephalitis in the tsunami stricken countries in Asia

Implications for Japanese encephalitis of the tsunami aftermath in combination with monsoon rains are much more speculative than those for malaria and dengue, and, if at all, they are geographically restricted to Sri Lanka.

In brief

  • Space spraying using handheld fogging machines
  • Health sector preparedness to deal with outbreaks
  • Procurement of repellents
  • Vaccination of children against JE in areas at risk

General

The virus that causes Japanese encephalitis (JE), an infection of the membranes around the brain, is transmitted by some mosquitoes of the genus Culex. These mosquitoes prefer to breed in vast expanses of freshwater, and normally are associated with flooded rice fields in the early stages of the cropping cycle. Key species are C. gelidus and C. tritaeniorrhynchus

These mosquitoes are NOT to be confused with the anopheline mosquitoes that transmit malaria. The culicine mosquitoes that transmit JE prefer to bite domestic animals rather than humans, and pigs are an important part of the transmission chain, as they serve as "amplifying" hosts for the virus.

There is a vaccine for JE, but it is expensive and requires two boosts after the initial vaccination.

JE in the tsunami stricken areas

JE is endemic in Sri Lanka, South India and other parts of Asia where rice production and pig rearing are combined. Outbreaks normally occur under circumstances of intense transmission, when the virus spills over from pigs into the human population.

In receptive disaster zones, pigs are likely to have been wiped out. As the monsoon rains in SE Sri Lanka gradually change the flooded areas from brackish to fresh water, culicine mosquito populations may build up which, in the absence of domestic animals, will revert to biting humans. Transmission may take place directly from ardeid birds (herons, egrets and similar birds that carry the virus) to humans.

Measures

Vaccination, particularly of children, is the most effective action to prevent outbreaks, but it is expensive, requires basic logistics and is onerous because of the need for two repeat vaccinations. Larviciding is not an option, because of the extent of the breeding places. Space spraying with hand held fogging machines can have an important function in keeping mosquito populations down. The health sector should be prepared to deal with JE cases once large stretches of flooded areas have changed from brackish to fresh water and a build up of the indicated culicine mosquito population is observed.

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