Control of schistosomiasis in the new Rahad Irrigation Scheme of Central Sudan.

As the new Rahad Irrigation Scheme in Central Sudan began its first agricultural season in 1978, the Blue Nile Health Project was being developed to prevent schistosomiasis and other water-associated diseases in the Rahad and Gezira-Managil schemes. Taken as an indication of overall transmission in the Rahad scheme, the prevalence of infection among children in the newly established schools was found initially to be 14% for Schistosoma mansoni and 1% for Schistosoma haematobium in 1980. In the older Gezira-Managil irrigation system nearby, where transmission had not been controlled there was also little S. haematobium but the prevalence of S. mansoni in school-aged children was rising above 70%. To avoid a similar future in the Rahad scheme an integrated control strategy was implemented in 1980 using chemotherapy and snail control, supported by safe water supplies in every village. Under this strategy the prevalence of S. mansoni in the schoolchildren was reduced below 10% by 1983 at an annual cost of less than $4 per capita, about $300 per square kilometer. S. haematobium remained at 1% in the schoolchildren in 1983. The major cost was for village water supplies with about 20% of the total going for snail control and 10% or less for chemotherapy. Over a third of the cost was for equipment and supplies purchased abroad, requiring hard currency. Economically feasible prevention of transmission in the long-term will require reduction of the annual cost to about $1 per capita. Cost reductions should be made primarily in operation and maintenance of the water supply systems and in snail control.

Protection of Sudanese irrigation workers from schistosome infections by a shift to earlier working hours.

Although schistosomiasis is an important occupational hazard for irrigation workers in Central Sudan, few measures have been found to protect them, short of abandoning the work. In an attempt to reduce their exposure to the large numbers of schistosome cercariae encountered in the water at midday, a group of Gezira canal cleaners were shifted to early morning working hours after being cured of their infections. They left the water each day at 10.00 hours, working from the canal banks thereafter. At the end of 6 months the prevalence of infections with Schistosoma mansoni was much lower in this group than in a similarly treated group with normal working schedules, indicating a practical way to protect irrigation and agricultural labourers.

Survival, growth and reproduction of the imported ampullarid snail Marisa cornuarietis in Central Sudan.

The ampullarid snail Marisa cornuarietis was imported to the Sudan in 1981 for evaluation as a biological control agent against the planorbid snails which transmit human schistosomes. In initial field studies in small protected ponds the generation time of M. cornuarietis was 4 months, as in Puerto Rico. The snails reached 4 cm in diameter after 1 year, compared to 3 cm in Puerto Rico. Their population density varied from 60 to 175 snails per metre of shore-line, compared to a similar pond in Puerto Rico where the stable density was about 115 snails per metre. The proportion surviving after 1 year was 0.03, less than the annual proportion surviving of 0.10 in Puerto Rico. Thus the preliminary results indicated that the ampullarid snails could establish strong populations in permanent habitats in central Sudan where there was adequate food, although it might take longer than it does in Puerto Rico.

Estimated risks and benefits from introducing Marisa cornuarietis into the Sudan.

As it has been proposed that Marisa cornuarietis, the ampullarid snail from the tropical Americas be used in the Sudan as a biological control agent against schistosomiasis, an estimate was made of the potential ecological hazards which might result from its widespread distribution in the Nile River Valley, and also of the potential benefits. The only foreseeable hazard would result from colonization of rice fields by the ampullarid snail and subsequent crop damage. However calculations on population dynamics indicated that Marisa cornuarietis would not be able to establish significant populations in rice fields in the Nile Valley as the flooded periods are too short. Thus the expected benefits of schistosomiasis control far outweigh any expected risks, and the ampullarid should be used in expanded field trials in the Gezira Irrigated Area as a control method for schistosomiasis.

Biological control of schistosome transmission in flowing water habitats.

Marisa cornuarietis was evaluated in Puerto Rico for control of schistosome transmission in flowing water. A population of Biomphalaria glabrata and their schistosome infections disappeared after introduction of 20,000 M. cornuarietis to an endemic stream, while in nearby untreated streams the B. glabrata population remained stable and the schistosome prevalence increased. This method cost U.S. $0.10 per capita for over a year of protection, 5%-10% of the cost of chemical control.

Schistosomiasis control in Puerto Rico: twenty-five years of operational experience.

A program to control schistosomiasis in Puerto Rico was initiated in 1953, using limited chemotherapy and snail control by environmental, biological and chemical means. At the same time, extensive programs of water supply, health education, and free latrine distribution were underway throughout the island. The impact of the program was evaluated initially by examinations of fecal samples from first-grade children until 1966, and subsequently by island-wide surveys using adult worm antigen for skin test on fifth-graders in 1963, 1969, and 1976. There was a decrease in the proportion of children reacting positively to the skin test from 24% in 1963 to 5% in 1976. The decrease in the proportion of positive skin test reactions was one and a half times as great in the area under snail control as in the rest of the endemic area, and most of the decrease outside the snail control program was due to improved water supply. Calibration tests indicated a decrease in prevalence among the entire population, if determined by multiple fecal exams, from 15% in 1963 to less than 4% in 1976. Thus the estimated number of persons passing eggs in Puerto Rico was about 100,000 in 1976, in a population of 3 million. The cost of snail control was minimized by emphasizing environmental and biological methods, showing that the disease can be controlled on a large scale with simple techniques. Eradication of the parasite from Puerto Rico is quite likely in the next few years with the advent of the new drug, oxamniquine, and would be a cheaper strategy than continued snail control.

Cost of snail control.

In the last 10 years, there has been general agreement that niclosamide (bayluscide) is the preferred molluscicide for control of the snails transmitting Schistosoma mansoni and Schistosoma haematobium. This chemical has been widely tested in pilot projects and is in use in expanded control projects in Brazil, Puerto Rico, Egypt, Iran, and other countries. A comparison of the results from six pilot projects in these countries was analyzed with particular attention to the costs of the programs, since the benefits were fairly similar in terms of rapid snail control. It was shown that costs were generally related to simple geographic parameters such as volume of snail habitat and distance between habitats. The annual costs in 1972 prices ranged from a minimum of US $1 per 100 m3 of snail habitat treated for dry regions with large irrigation systems, to a maximum of US $40 per 100 m3 treated in areas of high rainfall with only a few scattered, natural waterbodies. Use of the reported data for estimating the cost of current programs was demonstrated by projecting costs for Puerto Rico and the Sudan in 1978 prices.

Schistosomiasis in the Gorgol Valley of Mauritania.

Schistosomiasis may be increasing in West Africa due to the development of water-resource projects which were given a strong impetus by the disastrous Sahelian drought. This report concerns the existing epidemiology of schistosomiasis in West Africa for the Fourth Region of Mauritania, along the Gorgol River. In this area two reservoirs are proposed, to supply a new rice irrigation system. During May and November 1974, field surveys were made to determine the prevalence and intensity of schistosomiasis, and the relevant species of snails. The surveys were made as a basis for designing the irrigation systems to minimize transmission. The only snails found in the area were two species of Bulinus; therefore, the human population was tested for Schistosoma haematobium. A high prevalence of schistosomiasis was found in M'Bout, the town nearest the proposed reservoir at Foum Gleita. Prevalence rates were lowest in Kaedi near the confluence of the Gorgol and Senegal rivers. During the period between the first and second survey the incidence rate among children in M'Bout became very high (68%), probably because of increased water contact related to the rains that broke the long drought in August 1974.

Control of schistosomiasis in Guayama and Arroyo, Puerto Rico.

In 1953, a programme to control schistosomiasis mansoni was started in Guayama and Arroyo, Puerto Rico, employing, first, chemical and, later, both biological and chemical methods to control Biomphalaria glabrata, the snail host of Schistosoma mansoni. Sodium pentachlorophenate was the molluscicide, and an ampullarid snail, Marisa cornuarietis, was used for biological control in ponds and reservoirs. In addition some chemotherapy was given to infected persons. The prevalence of intestinal schistosomiasis was measured annually, sampling about one-third of the 6-year-old population in Guayama and Arroyo and in Caguas, an untreated area. Costs of the programme and the results are discussed in relation to similar projects in other parts of Puerto Rico. In Guayama and Arroyo the prevalence of schistosomiasis reached zero in 6-year-olds by 1966 despite the persistence of the disease in a nearby untreated area. Although this decline appeared related to the control effort, it is noted that a large decline also occurred in the untreated area, suggesting the influence of other factors such as economic development or improvements in sanitation.