Validation of a New Test for Schistosoma haematobium Based on Detection of Dra1 DNA Fragments in Urine: Evaluation through Latent Class Analysis

Open Access
Publisher Website
Google Scholar
Abstract
Diagnosis of urogenital schistosomiasis in chronically infected adults is challenging but important, especially because long term infection of the bladder and urinary tract can have dire consequences. We evaluated three tests for viable infection: detection of parasite specific DNA Dra1 fragments, haematuria and presence of parasite eggs for sensitivity (Se) and specificity (Sp). Over 400 urine specimens collected from adult volunteers in an endemic area in Western Nigeria were assessed for haematuria then filtered in the field, the filter papers dried and later examined for eggs and DNA. The results were stratified according to sex and age and subjected to Latent Class analysis. Presence of Dra1 in males (Se = 100%; Sp = 100%) exceeded haematuria (Se = 87.6%: Sp = 34.7%) and detection of eggs (Se = 70.1%; Sp = 100%). In females presence of Dra1 was Se = 100%: Sp = 100%, exceeding haematuria (Se = 86.7%: Sp = 77.0%) and eggs (Se = 70.1%; Sp = 100%). Dra1 became undetectable 2 weeks after praziquantel treatment. We conclude detection of Dra1 fragment is a definitive test for the presence of Schistosoma haematobium infection. The definitive test for schistosomiasis has been to detect parasite eggs in excreta. This is effective in children but as people age, it is difficult to find the eggs in spite of suspicion of infection. It also implies that adults have thrown off the infection, and therefore the infection is mainly one of children. However this is not the case as adults with chronic infections can develop severe bladder infection that can progress to bladder cancer. In clinical situations a sensitive test for urogenital schistosomiasis is important. We have recently shown that it is possible to detect schistosome species-specific DNA in urine, even in the absence of eggs in excreta. Here we use latent class analysis to compare sensitivity and specificity of three test procedures, haematuria, eggs in urine and specific DNA in urine in the absence of a gold standard. We show that the latter test is extremely promising for the diagnosis of urogenital schistosomiasis and should also be useful in field studies as it will be able to reveal infections in people frequently presumed to be uninfected. This new test indicated the presence of schistosomes in 10.7% of adults who did not pass eggs in urine specimens.