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Leishmaniasis in the Sudan Republic

12. Comparison of Experimental Leishmania donovani Infections in Phlebotomus papatasi (Diptera: Psychodidae) with Natural Infections Found in Man-Baited P. orientalis Captured in a Kala Azar Endemic Region of the Sudan^*

Donald Heyneman

A newly isolated human strain of Leishmania donovani from Malakal, Sudan, maintained in vivo was used to infect laboratory-reared Phlebotomus papatasi from Cairo and central Sudan. Flies of both strains were successfully infected by feeding through a mouse-skin membrane. Dissections showed nearly 100% infection and a uniformly high intensity of midgut infection (10,000 or more organisms per fly) at days 1 and 2 (the developmental phase), which fell to a lower level (5,000 to 10,000) during days 3 and 4 during division and migration through the gut, followed by rapid loss of leptomonads through the hindgut and diminishing numbers anteriorly on day 5. The numbers decreased to a level of about 100 per fly which was maintained in a decreasing proportion of exposed flies to approximately 20% over the 15-day observation period. Occasional flies showed a cluster of active flagellates at the anterior midgut, even in older infections. The two strains of P. papatasi tested are clearly poor hosts in terms of leptomonad development and survival, and presumably in transmission for the Malakal strain of human L. donovani.

Natural infections were found in 22 (1.88%) of 1,171 wild P. orientalis collected while biting man in a heavily endemic kala azar area of Upper Nile Province in the Sudan, but none of 690 P. papatasi or of local sandflies was infected.

Dissections revealed characteristics of infection in P. orientalis that were quite distinct from those in P. papatasi, with no evidence of a drop in parasite population in older infections, since nearly half the natural infections were at maximum levels in flies captured while taking an additional bloodmeal. Large numbers of both elongate, mature leptomonads and shorter, wider division forms were present. Significantly, there was a preponderance of strong anterior infections, with larger numbers of leptomonads in the cardia than in the stomach in 4 of the 22 flies and a greater concentration of leptomonads in the cardia than in the hindgut in all infected flies, in contrast to some of the laboratory-infected P. papatasi which showed greater concentrations in the hindgut than in the cardia. These observations and related epidemiological investigations clearly suggest that P. orientalis is the vector of human kala azar in this area of the Sudan.

^* From Research Project MR005.09-1603.7, Bureau of Medicine and Surgery, Navy Department, Washington 25, D.C. and supported in part by contract number 233(56) between the Office of Naval Research and the University of California, Los Angeles.

The opinions and assertions contained herein are the private ones of the author and are not to be construed as official or reflecting the views of the Navy Department or the naval service at large.

Present address: The G. W. Hooper Foundation, University of California Medical Center, San Francisco 22, California.