Inferring transmission trees to guide targeting of interventions against visceral leishmaniasis and post-kala-azar dermal leishmaniasis

Lloyd A. C. Chapman; Simon E. F. Spencer; Timothy M. Pollington; Chris P. Jewell; Dinesh Mondal; Jorge Alvar; T. Deirdre Hollingsworth; Mary M. Cameron; Caryn Bern; Graham F. Medley

. PKDL has therefore been recognised as a major 49 potential threat to the VL elimination programme in the ISC 50 (10), which has led to increased active PKDL case detection. 51 Nevertheless, the contribution of PKDL to transmission in 52 field settings still urgently needs to be quantified. 53 Although the incidence of asymptomatic infection is 4 to 54 17 times higher than that of symptomatic infection in the 55 ISC (21), the extent to which asymptomatic individuals con- (Fig. 1A) . The data from this study are fully de-105 scribed elsewhere (8, 31) . Briefly, month of onset of symptoms, 106 treatment, relapse, and relapse treatment were recorded for 107 VL cases and PKDL cases with onset between 2002 and 2010 108 (retrospectively for cases with onset before 2007), and year of 109 onset was recorded for VL cases with onset before 2002. There 110 were 1018 VL cases and 190 PKDL cases with onset between 111 January 2002 and December 2010 in the study area, and 413 112 VL cases with onset prior to January 2002. 113 Over the whole study area, VL incidence followed an epi-114 demic wave, increasing from approximately 40 cases/10,000/yr 115 in 2002 to ≥90 cases/10,000/yr in 2005 before declining to 116 <5 cases/10,000/yr in 2010 (Fig. 1B) . PKDL incidence fol-117 lowed a similar pattern but lagging VL incidence by roughly 118 2yrs, peaking at 30 cases/10,000/yr in 2007. However, VL 119 and PKDL incidence varied considerably across paras (aver-120 age para-level incidences: VL 18-124 cases/10,000/yr, PKDL 121 0-31 cases/10,000/yr, Table S5 ) and time (range of annual 122 para-level incidences: VL 0-414 cases/10,000/yr, PKDL 0-120 123 cases/10,000/yr, Fig. S15 ). ú CI = credible interval, calculated as the 95% highest posterior density interval †risk of subsequent VL/asymptomatic infection if susceptible ‡ based on assumed infectiousness § in the absence of background transmission and relative to living directly outside the case household.