[1] Univ Cambridge, Dept Vet Med, Cambridge CB3 0ES, England
[2] George Washington Univ, Dept Microbiol Immunol & Trop Med, Washington, DC 20037 USA
[3] George Washington Univ, Res Ctr Neglected Dis Poverty, Sch Med & Hlth Sci, Washington, DC 20037 USA
[4] Univ Melbourne, Fac Vet & Agr Sci, Melbourne Vet Sch, Dept Vet Biosci, Parkville, Vic 3010, Australia