VII. Summary Findings in the Paloich-Malakal Area Introduction Kala azar was first found in the Sudan in 1904(65) only a year after the disease was discovered and described in Algeria.(64) Shortly afterward, sporadic outbreaks were reported along the Ethiopian frontier of Blue Nile Province.(67–78) Increasingly intense outbreaks during the ensuing 20 years afflicted resident tribespeople, new settlers, and military patrols passing through uninhabited areas.(33) Although these sporadic, geographically localized outbreaks indicated an endemic zoonosis, regional spread and involvement of greater numbers suggested epidemic extension of the disease among nonimmune persons in new areas. In 1940, a serious outbreak with characteristics of a true epidemic was reported from Melut, Upper Nile Province.(79) The infection apparently was brought to the Southern Fung District about 1956 by Arab nomads who had traveled here for the first time in half a century or more. The disease was fatal in most cases, rapidly disseminated in the population, and marked by cutaneous and nasopharyngeal symptoms, short incubation, and a tendency to attack several family members or an entire village within a short period.(85) The pattern suggested local, perhaps direct, transmission. Epidemic episodes increased in frequency and severity during the 1950s, with peak outbreaks in Melut-Paloich (1952), Wadega-Kurmuk (1956), Paloich, and Southern Fung (1958). Kirk and Lewis considered Phlebotomus orientalis of the subgenus Larroussius, to be the probable vector, and that Phlebotomus (S.) clydei might or might not be a vector.(36,41,53,62) The former species was implicated on circumstantial grounds, the latter from a limited feeding experiment.(53) No information was available on the ecology, seasonal dynamics, flight habits, or other pertinent biological attributes of these possible vectors. No reservoir hosts were known, and prevention of kala azar transmission by insecticide spraying programs in the villages was fruitless. The seriously worried Minister of Public Health, Dr. Mohammed Ahmed Ali, urgently requested help in solving this growing problem, which not only afflicted whole tribal groups and villages but also endangered the entire plan for economic and agricultural development of the central Sudan. Of immediate concern was the program for resettling numerous nonimmune persons within the kala azar endemic region. Following an on-site tour of infected areas by the Minister of Public Health and the NAMRU-3 Director, Dr. John R. Seal, an agreement was reached for prompt epidemiologic research to discover the transmission pattern and source of infection and to suggest practical control measures. The main NAMRU-3 kala azar research laboratory was established in Malakal early in 1960, and the Paloich “Forward Field Laboratory” was opened near the end of the 1962 dry season. Full-scale efforts continued through the 1964 dry season. Work during the 1962 and 1963 rains contributed to knowledge of sandfly biology during the little-studied summer period. By the onset of the 1964 rains, the major epidemiologic and ecologic factors had been blocked out and confirmed by repeated studies, the vector had been established and proved experimentally, and several reservoir host species had been demonstrated. Leishmania donovani strains were isolated from three species of urban and wild rodents and from two species of wild carnivores, from Sudanese and American patients suffering from cutaneous and visceral manifestations, and from Phlebotomus orientalis captured as they bit man. The W.H.O. Leishmaniasis Reference Center later proved all these isolates to be identical to each other, serologically indistinguishable from the known agents of kala azar in the Sudan. Vector Studies Man-biting sandflies After we had searched at length in various biotopes, we first found sandflies biting man in a forest environment near Paloich, 160 km north of Malakal, a region long endemic for kala azar. Man-biting sandflies in this area fell into two epidemiologically distinct groups: one exclusively in Acacia-Balanites forests and in villages within or adjacent to these forests; the other largely restricted to human communities in grasslands and forests. The forest man-biting species were chiefly P. orientalis and Phlebotomus heischi. The latter was collected only in restricted portions of Acacia-Balanites forests, and its numbers were much less constant than those of P. orientalis. P. heischi adults were active earlier in the dry season (January to April) than those of P. orientalis (April to June); they were collected in small sectors of the forest and only in 1963 and 1964, being particularly common during the 1964 dry season. A few scattered Phlebotomus papatasi also fed on man in forests near villages, but these appeared to be chiefly stragglers. P. papatasi, the primary pest of man in grassland villages and in older villages within and near forests, was common near and in human habitations. Population densities in long-established grassland hamlets were particularly heavy. This species bit man voraciously, causing many persons to flee to open grass areas for respite and sleep. P. papatasi undoubtedly breeds in or near village huts, though precise information is lacking. No man-biting sandflies were found in open grassland away from villages or around nearby hafirs (artificial water basins). Epidemiologically important biological observations of P. orientalis made during our first two field seasons were amply confirmed in later field studies. P. orientalis adults first appeared in the middle of the dry season and increased considerably in numbers until the rains began, when their numbers dropped dramatically. Early records of man-biting began about the same week each year but the population decrease, which depended on the vagaries of the early rains, was more irregular. Ecologically, P. orientalis was strictly confined to...