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John D. Wilson, M.D.
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JAPANESE ENCEPHALITIS INFORMATION #3

 

JE disease: Mosquito-borne viral infection, similar to West Nile virus which has recently come to the US. The reservoir is pigs in JE (birds in West Nile). JE is endemic in much of southern Asia in spring, winter and fall, but is highly season and geography dependent. Infects many in an endemic area, but seriously affects few. Those who develop brain infection have a significant death and permanent disability rate.

JE vaccine: Expensive, safe; 2 doses 28 days apart.

Japanese encephalitis email correspondence among travel medicine doctors

I have recently been advised of a case of confirmed Japanese encephalitis in a New Zealand traveler. This 49 year old female was hospitalized in July, 2004, immediately on return to NZ from a trip of about 5 weeks to Japan, China and Hong Kong. The patient had not had any travel vaccinations. She traveled first to Japan (12 days), then China (3 weeks, including some urban stays and a trip to the Yangtze River for 4 days), and finally Hong Kong (2 days) before returning to New Zealand. All sleeping accommodations were air conditioned, except for 2 days of the trip (while traveling on trains in China). No other mosquito/insect bite precautions were taken; mosquitoes were seen, but no bites were noticed by the patient.

As the incubation period for Japanese encephalitis is 5-15 days, it is inferred that the patient acquired the disease in China. The main manifestation of illness in this case was a severe meningoencephalitis (brain infection) with permanent thinking impairment and paralysis.

Japanese encephalitis is an unusual disease for travelers to acquire in the region for such a short time. Of particular note is the fact that there did not appear to be extended travel into rural areas. Recently there have been two reports of Japanese encephalitis in nearby Hong Kong, also an unusual occurrence, emphasizing the need to advise all travelers to Asia fully on the benefits of preventative vaccination and protection against mosquito bites (and making this specific to an intended itinerary of travel).

Reply:
This unfortunate case raises an issue which I believe has not been definitively dealt with, and that is how rigid travel health advisors should be in extrapolating from epidemiological data when advising individual travelers. This becomes particularly pertinent when the consequences of contracting a disease can be catastrophic.

The usual advice that would have been given to the traveler described would have been that vaccination against Japanese encephalitis would not have been warranted, yet her lack of vaccination appears to have ruined her life. The evidence on the cost-effectiveness of meningococcal vaccine in the United States is that vaccination can never be justified on economic grounds, yet many parents sending their children to college are willing to pay for the vaccine.

If a traveler faces the risk, albeit very small, of an illness whose outcome may be death or permanent brain damage, then should the travel health advisor be concerned with the risk-benefit ratio of the intervention rather than the cost-benefit ratio?

Further comment
It happens that the measured risk of getting severe JE in China is less than 1 in a million. It's up to the practitioner and the traveler to decide whether 1 in a million means "there's still a chance." Some would take comfort in those odds, others would feel it was worth vaccinating against. Few would feel that 1,000,000 travelers should be vaccinated to prevent one case of JE.

Climate changes and increased commerce and travel between locales have made it increasingly hard to predict appearance of diseases in new locations (for example, West Nile virus in North America). Whether we should interpret this fact as a need to be more free with vaccine advice remains to be determined. An Israeli tourist acquired a severe case of JE in Thailand in 1989. This led Israeli public health authorities to recommend JE vaccine to all Israeli travelers to Thailand, even though the vaccine was not available in Israel at the time. Is this applied common sense and epidemiology, or a reaction to an anecdotal event? Which is the more valid way to prevent tragedy?
 

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  John D. Wilson, M.D. 1999-2016; Last Update 4/23/2016