1. a United States Army Medical Research Unit, Kenya , Box 401, APO AE 09831, U.S.A.
2. b Biomedical Sciences Research Centre , Kenya Medical Research Institute , Box 54840, Nairobi, Kenya
3. c Wilberforce OKEKA , Kakamega Forest Station , Box 88, Kakamega, Kenya
4. d ICAPB, Ashworth Laboratories , University of Edinburgh , Edinburgh, EH9 3JT, U.K.