[1] UNIV MALAYA,INST ADV STUDIES,KUALA LUMPUR 59100,MALAYSIA
[2] AGA KHAN UNIV,MED CTR,DEPT PAEDIAT,KARACHI 74800,PAKISTAN
[3] UNIV BRITISH COLUMBIA,BIOTECHNOL LAB,VANCOUVER,BC V6T 1Z3,CANADA
[4] UNIV ZURICH,INST MED MICROBIOL,CH-8028 ZURICH,SWITZERLAND