infectious diseases
Schistosomiasis
Diagnosis of Schistosomiasis
Microscopic examination of stool or urine (S. haematobium) for eggs Antigen tests Serologic tests Diagnostic testing is indicated for patients with symptoms of schistosomiasis and relevant epidemiologic exposure. Screening of asymptomatic people may be warranted for those exposed to fresh water in endemic areas. Schistosomiasis is diagnosed and parasite burden is estimated by microscopic examination of stool or urine (S. haematobium) for eggs. Repeated examinations using concentration techniques may be necessary. Geography is a primary determinant of species, so the location of exposure should be communicated to the laboratory. If the clinical picture suggests schistosomiasis but no eggs are found after repeated examination of urine or feces, intestinal or bladder mucosa can be biopsied to check for characteristic granulomas around embedded eggs. Tests for schistosomal antigens or DNA in blood, urine, or stool are particularly useful for schistosome eradication programs and in returning travelers with suspected infection. Most antigen detection tests are quantitative and antigen levels are correlated to parasite burden. Some antigen tests, such as the commercially available urine dipstick forS. mansoni, are qualitative. Serologic tests are sensitive and specific for infection, but do not provide information about worm burden, clinical status, or prognosis and do not distinguish active from resolved infection. Antibody tests thus are most useful for detecting infection in returning travelers and not helpful in patients who are residents of endemic areas. With returning travelers, serologic tests should be done ≥ 6 to 12 weeks after the last exposure to fresh water to allow time for maturation of the schistosomes into adults and for development of antibodies. Hepatosplenic schistosomiasis can be diagnosed by finding eggs in stool, intestinal tissue, or liver samples taken for biopsy with variable sensitivity as egg shedding can be intermittent in such patients. Typically, liver blood tests are normal. Ultrasonography may show periportal fibrosis and splenomegaly. Neuroschistosomiasis is diagnosed if there is infection at an extraneural site along with clinical and radiographic evidence of neurologic involvement. Schistosomes in biopsied central nervous system lesions, and/or a positive antibody test or polymerase chain reaction in cerebrospinal fluid are also diagnostic. 