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

Nonetheless, our results suggest that asymptomatic indi-382 viduals do contribute a small amount to transmission and 383 that they can "bridge" gaps between VL cases in transmission 384 chains, as the best-fitting model has non-zero asymptomatic 385 relative infectiousness. Superficially, this appears to conflict 386 with preliminary results of xenodiagnosis studies in which 387 asymptomatic individuals have failed to infect sandflies ac-388 cording to microscopy (44). However, historical (12, 45) and 389 experimental (46) data show that provision of a second blood 390 meal and optimal timing of sand fly examination are criti-391 cal to maximizing sensitivity of xenodiagnosis. These data 392 suggest that recent xenodiagnosis studies (11, 44), in which 393 dissection occurred within 5 days of a single blood meal, may 394 underestimate the potential infectiousness of symptomatic 395 and asymptomatic infected individuals. Occurrence of VL in 396 isolated regions where there are asymptomatically infected 397 individuals, but virtually no reported VL cases (27, 47), also 398 seems to suggest that asymptomatic individuals can generate 399 VL cases. However, it is possible that some individuals who de-400 veloped VL during the study went undiagnosed and untreated, 401 and that we have inferred transmissions from asymptomatic 402 individuals in locations where cases were missed. We will in-403 vestigate the potential role of under-reporting in future work. 404