Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 35-13: Schistosomiasis (Bilharziasis) + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ History of freshwater exposure in an endemic area Acute schistosomiasis: fever, headache, myalgias, cough, urticaria, diarrhea, and eosinophilia Intestinal schistosomiasis: abdominal pain, diarrhea, and hepatomegaly, progressing to anorexia, weight loss, and features of portal hypertension Urinary schistosomiasis: hematuria and dysuria, progressing to hydronephrosis and urinary infections Diagnosis: characteristic eggs in feces or urine; biopsy of rectal or bladder mucosa; positive serology +++ General Considerations ++ Intestinal schistosomiasis, with infection of mesenteric venules, caused by Schistosoma mansoni, which is present in Africa, the Arabian peninsula, South America, and the Caribbean Schistosoma japonicum, which is endemic in China and Southeast Asia Schistosoma mekongi, which is endemic near the Mekong River in Southeast Asia Schistosoma intercalatum and Schistosoma guineensis, which occur in parts of Africa Urinary schistosomiasis, with infection of venules of the urinary tract Caused by Schistosoma haematobium Endemic in Africa and the Middle East Transmission is focal, with greatest prevalence in poor rural areas Humans are infected with schistosomes after contact with freshwater containing cercariae released by infected snails Chronic infection can result in scarring of mesenteric or vesicular blood vessels, leading to portal hypertension and alterations in the urinary tract Acute schistosomiasis May occur in previously uninfected individuals Febrile illness develops 2–8 weeks after infection +++ Demographics ++ Affects more than 200 million persons worldwide, leads to severe consequences in 20 million persons and about 100,000 deaths annually Prevalence of infection and illness typically peaks at about 15–20 years of age + Clinical Findings Download Section PDF Listen +++ ++ Cercarial dermatitis Localized erythema develops in some individuals, which can progress to a localized pruritic maculopapular rash that persists for some days Dermatitis can be caused by human schistosomes and, in nontropical areas, by bird schistosomes that cannot complete their life cycle in humans (swimmer's itch) Acute schistosomiasis (Katayama syndrome) A febrile illness may develop 2–8 weeks after exposure in persons without prior infection, most commonly after heavy infection with S mansoni or S japonicum Presenting symptoms and signs include Acute onset of fever Headache Myalgias Cough Malaise Urticaria Diarrhea, which may be bloody Hepatosplenomegaly Lymphadenopathy Pulmonary infiltrates Localized lesions may occasionally cause severe manifestations, including CNS abnormalities and death Chronic schistosomiasis Many infected persons have light infections and are asymptomatic However, an estimated 50–60% of patients have symptoms and 5–10% have advanced organ damage Asymptomatic infected children may suffer from anemia and growth retardation Intestinal schistosomiasis Symptomatic patients typically experience abdominal pain, fatigue, diarrhea, and hepatomegaly Over years, anorexia, weight loss, weakness, colonic polyps, and features of portal hypertension develop Late manifestations include hematemesis from esophageal varices, hepatic failure, and pulmonary hypertension Urinary schistosomiasis May present within months of infection with hematuria and dysuria, most commonly in children and young adults Fibrotic changes in the urinary tract can lead to hydroureter, hydronephrosis, bacterial urinary infections and, ultimately, kidney disease or bladder cancer + Diagnosis Download Section PDF Listen +++ ++ Microscopic examination of stool or urine for eggs, evaluation of tissue, or serologic tests establish the diagnosis Characteristic eggs can be identified on smears of stool or urine The most widely used stool test is the Kato-Katz technique Quantitative tests that yield more than 400 eggs per gram of feces or 10 mL of urine are indicative of heavy infections with increased risk of complications Diagnosis can also be made by biopsy of the rectum, colon, liver, or bladder Serologic tests include an ELISA available from the CDC that is 99% specific for all species, but cannot distinguish acute and past infection Serology is of limited use in endemic settings, but can be helpful in travelers from nonendemic regions Point-of-care assays to detect circulating schistosome antigens in serum and urine are also available; the most widely used tests target circulating anodic and cathodic antigens In acute schistosomiasis, leukocytosis and marked eosinophilia may occur; serologic tests may become positive before eggs are seen in stool or urine Liver biochemical tests and imaging of the liver used to evaluate extent of intestinal disease Ultrasonography and other imaging studies used to evaluate extent of urinary disease + Treatment Download Section PDF Listen +++ ++ Praziquantel Drug of choice Dosage: 40 mg/kg (in one or two doses) orally for 1 day for S mansoni, S haematobium, S intercalatum, and S guineensis infections 60 mg/kg (in two or three doses) orally for 1 day for S japonicum and S mekongi Cure rates are generally > 80% after a single treatment, and those not cured have marked reduction in the intensity of infection Drug may not prevent illness when given after exposure; a repeat course after a few weeks may be appropriate for recent infections May be used during pregnancy Resistance has been reported Toxicities include abdominal pain, diarrhea, urticaria, headache, nausea, vomiting, and fever, and may be due both to direct effects of the drug and responses to dying worms With severe disease, use of corticosteroids in conjunction with praziquantel may decrease complications Alternative therapies Oxamniquine for S mansoni infection Metrifonate for S haemotobium infection Both of these drugs have limited availability (not available in the United States), and resistance may be a problem No second-line drug is available for S japonicum infections Artemether Has activity against schistosomulae and adult worms May be effective in chemoprophylaxis However, it is expensive, and long-term use in malarious areas might select for resistant malaria parasites + Outcome Download Section PDF Listen +++ +++ Follow-Up ++ Repeat examinations for eggs should be done about every 3 months for 1 year after therapy, with re-treatment if eggs are seen +++ Prevention ++ Travelers to endemic areas should avoid freshwater exposure Vigorous toweling after exposure may limit cercarial penetration Community control of schistosomiasis includes improved sanitation and water supplies, elimination of snail habitats, and intermittent treatment to limit worm burdens +++ Prognosis ++ Acute schistosomiasis usually resolves in 2–8 weeks + References Download Section PDF Listen +++ + +Nelwan ML. Schistosomiasis: life cycle, diagnosis, and control. Curr Ther Res Clin Exp. 2019 Jun 22;91:5–9. [PubMed: 31372189] + +Olveda RM et al. Efficacy and safety of praziquantel for the treatment of human schistosomiasis during pregnancy: a phase 2, randomised, double-blind, placebo-controlled trial. Lancet Infect Dis. 2016 Feb;16(2):199–208. [PubMed: 26511959] + +Utzinger J et al. New diagnostic tools in schistosomiasis. Clin Microbiol Infect. 2015 Jun;21(6):529–42. [PubMed: 25843503] + +Weerakoon KG et al. Advances in the diagnosis of human schistosomiasis. Clin Microbiol Rev. 2015 Oct;28(4):939–67. [PubMed: 26224883]