4 Control of Schistosomiasis

Schistomiasis is a disease caused by digenetic trematodes that belong to the family Schistosomatoidae. Five species of Schistosomes are involved in human infection. The three principal agents are Schistosoma mansoni and S. japonicum which are responsible for intestinal schistosomiasis and S. haematobium, the aetiologic agent of urinary schistosomiasis. The other two species responsible for intestinal disease though with low frequency are S. intercalatum and S. mekongi. The disease affects about 240 million people worldwide while an estimated 779 million people (more than 10% of the world population) are at the risk of infection. About 120 million people infected with schistosomiasis are estimated to be symptomatic while about 20 million develop severe diease.The disability-adjusted life years (DALYs) due to schistosomiasis is about 1.7-4.5 million while between 150,000 to 280,000 people are known to die as a consequence of the disease per year. Africa accounts for 85% of the disease burden (Steinmann et al., 2006; WHO, 2002). Although, schistosomiasis is a rural focal disease typically associated with poor rice farmers and fishermen in the tropics, it is increasingly been reported among Europeans with a history of travel to endemic areas in Africa and Asia. It is transmitted by snails found in cercariae infested fresh water streams. Snails belonging to the species Bulinus, Biomphalaria and Onchomelania are the vectors of S. haematobium, S. mansoni and S. japonicum respectively. The cardinal objective in the control of schistosomiasis is the reduction of morbidity and mortality to levels below public health significance. Over the years, emphasis has shifted from the non-realizable goal of eradication to the more realistic goal of morbidity control. In this context, Gemmel et al (1986), defined “a control programme” as the “implementation of specific measures by a disease control authority to limit the incidence of the disease”. Such implementation may involve specific technical interventions and perhaps legislation to enforce compliance. The success of this type of approach is predicated on an accurate ecological diagnosis, that is, a diagnosis of the human community, its parasitological characteristics, its physico-geographical environmental attributes and man’s behavioural attitudes and customs (Davis, 1981). The enormous morbidity associated with schistosomiasis which ranks it next to malaria in terms of public health significance re-emphasises the need for a coordinated and sustainable means for the control of the disease. There is a consensus of opinion that the control of the disease should be integrated. In this model of control, King (2009) identified the applicable approaches as:  Population based chemotherapy  Snail control which involves habitat modification and use of plant and chemical molluscicides,