Ari's Planet

Another vaccine-preventable disease in Asia. Most of what you need to know as a traveler is here:

http://www.cdc.gov/ncidod/dvbid/jencephalitis/qa.htm

See also my vaccinations page.

It's quite hard to find good data on actual risk to the virus. Basically, the mosquito breeds in cultivated (flooded) rice paddies and the virus resides and multiplies in pigs and birds. You are at risk in areas near cultivated rice paddies with pigs and birds in southern Asia. The further away you are from such areas the lower your risk, presumabely because mosquitos can only travel a certain distance. Because cultivation is seasonal risk is also seasonal, with infections peaking during the cultivation season. In SEA, this would be during the wet season, e.g., in Thailand, from around July through October. In the area of Pai, rice fields were not being cultivated when I visited in late February 2008, but riding the bus from Chiang Mai to Chiang Rai, which lies east of Pai, I saw actively cultivated rice paddies. The risk is higher during the transmission season in SEA, which the CDC gives as May to October. While the risk is lower during the dry season, I expect it is not zero. I couldn't find an article that gives good seasonal information in a simple format, the closest and most recent data are for Malaysia in Wong SC 2008 et al (see reference below), and there are several articles that studied infections in parts of India.

http://www.ncbi.nlm.nih.gov/pubmed/18291002?ordinalpos=1&itool=EntrezSys...
Trop Med Int Health. 2008 Jan;13(1):52-5. PMID: 18291002
A decade of Japanese encephalitis surveillance in Sarawak, Malaysia: 1997-2006.Wong SC, Ooi MH, Abdullah AR, Wong SY, Krishnan S, Tio PH, Pek PC, Lai BF, Mohan A, Muhi J, Kiyu A, Arif MT, Cardosa MJ.