Southeast Asia is attracting attention as a source of potentially dangerous emerging infections, not least influenza, but also dengue, Nipah, and possibly the causative agent of severe acute respiratory syndrome (SARS). The most important cause of epidemic encephalitis worldwide is the mosquito-borne Japanese encephalitis virus (JEV), a flavivirus allied to West Nile virus. Solomon et al. have probed the geographical distribution of JEV strains across Asia since the first reported outbreak in Japan in the 1870s. All five genotypes identified occur simultaneously in Indonesia and Malaysia, whereas only evolutionarily more recent strains have spread out of this region. The Japanese epidemic was devastating and affected people of all ages, as flaviviruses do when they reach an immunologically naïve population. By contrast, in Malaysia, it is rarely epidemic, suggesting a long-standing association with humans here and pointing to the Indonesia-Malaysia region as the nidus of JEV. -- CA
J. Virol. 77, 3091 (2003).
