A total of nine cases of serologically confirmed Japanese encephalitis occurred in five units of U. S. Marines stationed in Thailand in July and August 1972, and 27% of 2,101 Marines in these units had evidence of recent JEV infection. The apparent-to-inapparent infection ratio of 1:63 in this epidemic is higher than that previously described in Asians, but similar to that previously estimated in U. S. troops in Korea. This study confirms the human virulence of Japanese encephalitis virus in Thailand and provides strong evidence that Thai strains are of similar human virulence to strains infecting Americans in more northern latitudes in earlier studies.
Present address (address for reprint requests): Division of Preventive Medicine, Walter Reed Army Institute of Research, Washington, D. C. 20012.
Present address: Department of Virus Diseases, Walter Reed Army Institute of Research, Washington, D. C. 20012.
Present address: Letterman Army Institute of Research, Presidio of San Francisco, California 94129.
Present address: University of Alabama Medical Center, Birmingham, Alabama 35233.
Present address: U. S. Army Medical Research and Development Command, Washington, D. C. 20310.