Increase in transmissibility following reexposure to sand fly bites. A, Transmission of Leishmania donovani strain Mongi from sick hamsters to Lutzomyia longipalpis sand flies in the initial feeds on 2 sites on the abdomen and to a new set of flies exposed to the same sites 24 hour later. Nine hamsters were exposed on 2 sites, and 2 hamsters were exposed on 4 sites. Data are percentages of blood-fed flies fed on individual sites positive for parasites in the first and second feeds, with mean values denoted by bars (data are for 26 sites and 11 hamsters). B, Parasite loads as determined by titration culture in 4-mm skin biopsy specimens collected from the sites on the abdomen exposed 2 times to sand fly bites (data are for 16 sites and 8 hamsters), from adjacent nonexposed sites on the abdomen (11 sites and 8 hamsters), and from abdominal sites from sick hamsters never exposed to sand fly bites (8 sites and 2 hamsters). Data are mean values ± SD, with maximum and minimum values. C, Parasite loads as determined by quantitative polymerase chain reaction (qPCR) in 4-mm skin biopsy specimens collected from the sites on the abdomen exposed 2 times to sand fly bites (data are for 14 sites and 7 hamsters), from adjacent nonexposed sites on the abdomen (5 sites and 3 hamsters), and from sick hamsters never exposed to sand fly bites (8 sites and 2 hamsters). Data are mean values ± SD, with maximum and minimum values. D, Transmission of L. donovani strain Mongi (solid lines) or L. donovani 1S (dotted lines) from sick hamsters to flies in the initial feeds on 2 sites on the abdomen and to a new set of flies exposed to the same sites or 2 adjacent, previously nonexposed sites 24 hours later. Data are the percentages of the total number of the blood-fed flies fed on the 2 sites in each group that were positive for parasites, with mean values denoted by bars (data are for 8 sites/group and 8 hamsters).