Schistosoma epidemiology & diagnosis José Manuel Correia da Costa INSA National Institute of Health Dr. Ricardo Jorge
Brindley PJ & Hotez PJ (2013) Break Out: Urogenital Schistosomiasis and Schistosoma haematobium infection in the Post-Genomic Era. PLoS Negl Trop Dis 7(3). More than 90% of the roughly 200 million cases of schistosomiasis occur in Africa, of which approximately twothirds are caused by Schistosoma haematobium, the etiologic agent of urogenital schistosomiasis. Charles King and his collegues have suggested that the number of cases of S. haematobium may be much greater than previously believed, even possibly double or triple that of earlier prevalence estimates. If confirmed, urogenital schistosomiasis may represent the most common infection or even adverse health condition in sub-saharan Africa. Female genital schistosomiasis (FGS) is associated with contact bleeding, discharge, pain on intercourse, and secondary infections and diminished fertility; it is also a source of shame and stigma. FGS is not a rare condition one estimate suggested that of the estimated 70 million children currently infected with S. haematobium, approximateley 19 million girls and women will eventually develop FGS in the coming decade. FGS may represent one of the most common gynecological conditions in Africa. S. haematobium eggs have now been further identified as a Group 1 carcinogen responsible for a unique squamous cell carcinoma, which is widespread in S. haematobium-endemic areas. S. haematobium also exerts important host endocrine effects A full consideration of these and other chronic morbidities that use disability-adjusted life years (DALYs) as a metric suggests that chronic urogenital schistosomiasis may equal or even exceed malaria or other better-known conditions in terms of its diseses burden in Africa. Despite its overwhelming public health importance and its well-established links to HIV/AIDS and cancer, S. haematobium has been labeled the neglected schistosome.
Theodor Bilharz Schistosomiasis is an ancient scourge of mankind, depicted graphically in papyri from Pharaonic Egypt, and known from human remains over 2000 years old from China. Schistosomiasis or bilharzia is a common intravascular infection caused by Schistosoma trematode worms; Hieroglyfic script. Kahun papyrus Human Schistosomiasis is caused by one of 5 species: Schistosoma haematobium; Schistosoma mansoni; Schistosoma japonicum; Schistosoma intercalatum; Schistosoma mekongi. Schistosoma malayensis? Schistosome transmission requires contamination of water by faeces or urine containing eggs, a specific freshwater snail as intermediate host, and human contact with water inhabited by the intermediate host snail. Schistosomiasis transmission is highly dependent on environemental conditions, particularly those affecting the snail host. Climate change will alter aquatic environments and subsequentelly the transmission and distribution of waterborne diseases. Schistosome infections cause chronic and debilitating diseases also associated with anaemia, chronic pain, diarrhoea, exercise intolerance, undernutrition; female urogenital schistosomiasis may be risk factor for HIV infection.
How is schistosomiasis acquired? 1- Cercariae, free-swemming larval stages enter in the body after skin penetration; 2- Schistosomulae migrates through the tissues to the liver. Schistosoma life cycle University of Cambridge pictures
How is schistosomiasis acquired? Schistosoma life cycle
Where is schistosomiasis acquired? Global distribution of schistosomiasis. Adapted from Gryseels et al.2006 Infection is usually acquired through activities such as swimming, bathing, fishing, farming and washing clothes. Intermediate snail hosts are more likely to inhabit still to moderately flowing fresh water and infection increases exponentially with length of time in contact with water, peaking at 30 minutes.
Current global distribution of schistosomiasis, stratified according to country-specific prevalence estimates. Source: Steinmann et al., 2006 & Utzinger et al., 2009.
How is schistosomiasis diagnosed? Microscopic examination of excreta (stool and urine) remains the gold standard test for diagnosis of schistosomiasis albeit with some limitations. Formalin based techniques for sedimentation and concentration may increase the diagnostic yield. Kato-Katz thick smear stool. Schistosoma haematobium eggs are released in urine and detected by microscopy in a urine sample concentrated by sedimentation, centrifugation or filtration and forced over a filter. Sample collected between 10 am and 2 pm. haematobium intercalatum japonicum mekongi Calcified egg Calcified egg Specific and highly sensitive PCR to detect parasite DNA in faeces or sera and plasma. The miracidium hatching test. Biopsy of bladder or rectal mucosa. Imagiology. mansoni Antibody detection: useful in a few specific circumstances, but its application is limited. Epidemiological value. It is important for diagnosis in travellers. Cercarial antigen; SWAP; SEA; circulating adult worm or egg antigens; circulating cathodic antigen.
Key indicators for positive diagnosis of Schistosomiasis Medical history: Have you travelled to or emigrated from an endemic country recentely? If so from where? Have you been in contact with a freshwater source (lakes, rivers or streams)? (Patients returning/emigrating from Africa or the Middle East may have intestinal or urinary schistosomiasis and those from Asia or South America may have intestinal schistosomiasis). Physical examination: urticarial rash; hepatomegaly; lymphadenopathy.. Laboratory investigations: Stool/urine examination for schistosome eggs Full blood count: eosinophilia (>80% of patients) with acute infections; anaemia and thrombocytopenia. Coagulation profile: prolonged prothrombin time. Raised urea and creatinine may be evident Serology: may be diagnostic in patients in whom no eggs are present. Radiology/imagiology
How can be schistosomiasis controlled? Consensus: Schistosomiasis can be controlled in a coordinated approach with treatment on large scale with safe and effective drugs at regular intervals: Other operating components including provision Potable water Adequate sanitation Hygiene education Snail control Engels et al., Acta Tropica, 82, 2002
Long term commitment is terminology reserved for marriage, politics, religion and schistosomiasis control. Kenneth E. Mott, Parasite Diseases Programme, World Health Organization, 1989
Additional educational resources: Parasites schistosomiasis dpdx (www.cdc.gov) Health topics schistosomiasis (www.who.int) www.path.cam.ac.uk/~schisto/schistosoma/index.htlm University of Cambridge OBRIGADO