Schistosomiasis

Abstract

Schistosomiasis, a neglected tropical disease, is caused by the blood fluke that resides in the blood vessels in the human hosts. It presents as an acute, but mostly chronic, illness and is commonly found in the least developed countries with poor healthcare systems. Forty countries in Africa were endemic for schistosomiasis in sub-Saharan Africa (SSA) in 2010. Of the five species, Schistosoma haematobium, S. mansoni, S. japonicum, S. intercalatum and S. mekongi, that can infect humans, it is S. haematobium which causes urogenital schistosomiasis and S. mansoni and S. japonicum which cause intestinal schistosomiasis, which have public health importance, being responsible for most of the disease in SSA. Children, women and farmers in rural communities who depend on water contact for recreational, domestic or occupational activities are most vulnerable to the infection. Cross-border movements from unstable and conflict zones in SSA have contributed to the spread of the disease to previously non-endemic foci, and emigration from rural areas into the cities for economic opportunities has introduced the disease into some urban areas. Schistosomiasis causes around 4.5 million DALYs annually, with around 90 % of the burden of disease concentrated in SSA. Annual loss from disability due to schistosomiasis in Africa was estimated to be nearly half a billion US dollars approximately 70 % of the global cost. The life cycle involves an intermediate planorbid freshwater snail hosts – Bulinus truncatus and Biomphalaria pfeifferi – in the transmission of the infection with sexual and asexual stages. Man is the definitive host. Pathology and clinical morbidity of schistosomiasis are caused by eggs trapped in tissues and symptoms and signs of the disease present among other things, as haematuria in urinary schistosomiasis and abdominal pain, diarrhoea which can be bloody and blood in stool in intestinal schistosomiasis. Long-term complications from schistosomiasis include urinary tract infections, bladder calcification, hydronephrosis/hydroureter, kidney failure, lesions of the liver, portal vein, and spleen, leading to periportal fibrosis, hepatomegaly, splenomegaly, pipe-stem portal fibrosis, ascites, nodules in the vulva and bladder cancer. Microscopic examination for parasite eggs in the urine or stool is considered definitive for the diagnosis of the infection. Control of schistosomiasis is by transmission and morbidity control using health education, safe water supply, mollusciding, environmental management, chemotherapy praziquantel (PZQ) as drug of choice or combination of these measures. Whether or not schistosomiasis can only be controlled or can be eliminated using the current MDA with anthelminthes is an ongoing debate.