[1] Imperial Coll Sch Med, Dept Infect Dis Epidemiol, London W2 1PG, England
[2] Natl Inst Med Res, Dar Es Salaam, Tanzania
[3] Vet Labs Agcy, Ctr Epidemiol & Risk Anal, Addlestone KT15 3NB, Surrey, England
[4] Case Western Reserve Univ, Ctr Global Hlth & Dis, Cleveland, OH 44106 USA