In Paloich District of Upper Nile Province, Sudan, an area with a long history of heavy kalaazar endemicity, no Leishmania infection was found in Phlebotomus papatasi and laboratory experiments suggest that this sandfly species is an inefficient vector of strains of L. donovani from man in this Province.
Pure pools of P. orientalis (average 6 or 7 flies per pool) from small villages showed a remarkably high infection rate—30 positives in 180 pools examined (16.7%). In forested areas within a mile of these villages, 35 of 347 (10.1%) P. orientalis pools were infected. (Individual dissection of 1,150 P. orientalis by Donald Heyneman6 revealed a comparable rate of infection and heavy, anterior concentrations of leptomonads, indicating the efficiency of this sandfly as a vector.) Of the hamsters into which infected sandfly pools were inoculated, 54% developed a visceral leishmaniasis clinically and pathologically identical to that produced by Leishmania donovani in these animals. Since all sandflies were collected while biting humans in an area of heavy kalaazar endemicity, this organism is probably L. donovani. Four Nile Grass Rats, Arvicanthis niloticus luctuosus Dollman, were also found naturally infected with visceral leishmaniasis in forest sites in which numerous infected P. orientalis were taken.
No man-biting sandflies were found in grasslands, or in forests within a mile of the Nile. P. orientalis was widely distributed inland in Acacia and Acacia-Balanites forests, as well as in small and larger villages in forest clearings and close to forests. In villages away from forests, P. orientalis was less common or absent. Leishmania infections were found in P. orientalis wherever this sandfly occurred.
P. papatasi was present in established villages and was sometimes a serious pest. Except in a single locality about 200 yards from a village where small numbers of P. papatasi were taken, this species was extremely rare or absent in forested areas.