Schistosomiasis mapping, North Sudan

Situation:

Human schistosomiasis, a water-borne disease commonly known as bilharzia, is mainly caused by two species of blood flukes (called schistosomes): Schistosoma mansoni causing intestinal schistosomiasis and S. haematobium causing urinary schistosomiasis. The schistosomes require a snail intermediate host in which to undergo development. This ties transmission of the disease to places where people and snails come together in the same water habitat. Hence, schistosomiasis tends to be common in rural communities where contact with fresh water-bodies is an inevitable occurrence. The disease is caused primarily by schistosome eggs deposited by adult worms in the blood vessels surrounding the bladder or intestines, depending on the specific species. S. haematobium causes bladder wall pathology, leading to ulcer formation, hematuria, and dysuria. Granulomatous changes and ulcers of the bladder wall and ureter can lead to bladder obstruction, secondary urinary tract infections and subsequent bladder calcification, renal failure, lesions of the female and male genital tracts. The morbidity commonly associated with S. mansoni infection includes lesions of the liver, portal vein, and spleen, leading to periportal fibrosis, portal hypertension, hepatosplenomegaly, and ascites. Schistosomiasis also causes chronic growth faltering and can contribute to anaemia. Diagnosis is typically made by finding the characteristic spined eggs in urine (S. haematobium) or stool (S. mansoni). Schistosomiasis control programs aim to reduce the incidence of infection and associated morbidity and mortality, rather than to halt transmission entirely. The main strategy for controlling morbidity due to schistosomiasis is based on chemotherapy using praziquantel. Even though re-infection may occur after treatment, the risk of developing severe organ pathology is diminished and even reversed in young children.

Sudan was one of the first African countries where schistosomiasis control was attempted. Egyptian labourers who went to Sudan to dig the canals for the Gezira irrigation scheme were screened and treated with antimony potassium tartrate. Despite this, the prevalence of schistosomiasis gradually increased among the local farmers; first infections were caused by Schistosoma haematobium, followed by S. mansoni. Despite intermittent efforts at control, schistosomiasis continues to be a major public health problem in Sudan, with an estimated five million people infected. A comprehensive review of schistosomiasis in Sudan was published by WHO in 1987, using historical data to depict the distribution of schistosomiasis throughout the country. This indicated that south of the 9th degree latitude S. mansoni is very common whereas the largest endemic area of S. haematobium is to be found between the 9th and 16th degree latitudes.

Lack of knowledge on the distribution and prevalence of schistosomiasis is hampering control efforts in some states of Sudan. Though praziquantel is available from the government, local health authorities are often uncertain which areas and age groups need to be targeted with preventive chemotherapy. In early 2008, Malaria Consortium was approached by the Gedaref and Kassala state MoHs for technical assistance on carrying out schistosomiasis prevalence surveys, developing state-wide risk maps and formulating an intervention strategy based on this new evidence. In Gedaref specifically, there is evidence through routine health facility surveillance that schistosomiasis has spread from the traditional areas associated with gravity fed irrigation schemes to other localities in the state.

Response:

Funded by the Common Humanitarian Fund, Malaria Consortium is supporting schistosomiasis prevalence surveys during May and June 2008 in El Fau, Gedaref, East Galabat and West Galabat localities in Gedaref State and in New Halfa, Nahr Atbara, Hashm ElGirba and Kassala localities in Kassala State. Data from these surveys will be combined with available climate and environmental data to develop risk maps to allow targeting of preventive chemotherapy to populations at risk. Malaria Consortium’s experience of supporting schistosomiasis control programmes in a number of other African countries will guide formulation of appropriate intervention strategies for these settings in North Sudan.