[1] NATL INST HLTH, DEPT SAFETY RES BIOLOG, TOKYO 208, JAPAN
[2] NATL INST HLTH, DIV EXPT ANIM RES, TOKYO 208, JAPAN
[3] NATL INST HLTH, TSUKUBA PRIMATE CTR MED SCI, TSUKUBA, IBARAKI 305, JAPAN
[4] NIPPON INST BIOL SCI, TOKYO 198, JAPAN
[5] UNIV TOKYO, FAC AGR, DEPT VET MICROBIOL, BUNKYO KU, TOKYO 113, JAPAN