Diagnosing Schistosomiasis by Detection of Cell-Free Parasite DNA in Human Plasma

Abstract

IntroductionSchistosomiasis (bilharzia), one of the most relevant parasitoses of humans, is confirmed by microscopic detection of eggs in stool, urine, or organ biopsies. The sensitivity of these procedures is variable due to fluctuation of egg shedding. Serological tests on the other hand do not distinguish between active and past disease. In patients with acute disease (Katayama syndrome), both serology and direct detection may produce false negative results. To overcome these obstacles, we developed a novel diagnostic strategy, following the rationale that Schistosoma DNA may be liberated as a result of parasite turnover and reach the blood. Cell-free parasite DNA (CFPD) was detected in plasma by PCR.Methodology/Principal FindingsReal-time PCR with internal control was developed and optimized for detection of CFPD in human plasma. Distribution was studied in a mouse model for Schistosoma replication and elimination, as well as in human patients seen before and after treatment. CFPD was detectable in mouse plasma, and its concentration correlated with the course of anti-Schistosoma treatment. Humans with chronic disease and eggs in stool or urine (n = 14) showed a 100% rate of CFPD detection. CFPD was also detected in all (n = 8) patients with Katayama syndrome. Patients in whom no viable eggs could be detected and who had been treated for schistomiasis in the past (n = 30) showed lower detection rates (33.3%) and significantly lower CFPD concentrations. The duration from treatment to total elimination of CFPD from plasma was projected to exceed one year.Conclusions/SignificancePCR for detection of CFPD in human plasma may provide a new laboratory tool for diagnosing schistosomiasis in all phases of clinical disease, including the capacity to rule out Katayama syndrome and active disease. Further studies are needed to confirm the clinical usefulness of CFPD quantification in therapy monitoring.

Diagnostic and prognostic value of cell free circulating Schistosoma mansoni DNA: an experimental study

“…Similar results were reported by Wichmann et al (2009) who evaluated the Schistosoma circulating free DNA concentration in mice experimentally infected with S. mansoni and treated by praziquantel 42 days post infection, they found initial increase followed by progressive decrease till complete clearance in Schistosoma circulating free DNA level 138 days post treatment. In human, Wichmann et al (2009; purposed that, it may take more than one year until Schistosoma circulating free DNA becomes entirely undetectable as inactive eggs may release DNA with very slow kinetics. The greater number of eggs in humans with chronic disease may be responsible for a considerably longer duration until Schistosoma circulating free DNA is totally eliminated (Kato-Hayashi et al 2013).…”

Schistosomiasis

“…12 In chronic condition, symptoms would include blood in feces or urine, and can sometimes occur in the form of bladder cancer, liver cirrhosis, and esophageal varices. 11,14 Common signs and symptoms of S. Hematobium infection include : hematuria, dysuria, nocturia, proteinuria, leukocyturia, hydroureter, and hydronephrosis. In a more rare occurence, hematospermia could also be found.…”

“…15 During bladder biopsy, bladder calcification, bladder neck fibrosis, and bladder cancer could also be found. 11,14 Hepatic schistosomiasis or schistosomal hepatopathy is a chronic sign of S. Mansonia and S. Japonicum infection, which can cause liver fibrosis in the future.…”

“…Biopsy is done especially in patients with positive clinical presentations, but without eggs finding in examinations. 11 The diagnosis of Schistosomiasis in acute phase is very difficult, therefore a diagnosis model that can detect the prescence of parasite in any stage of its life cycle is needed. A study showed that Cell-free parasite DNA (CFPD) method was able to detect the prescence of schistosoma DNA in blood plasma on every stage of its life cycle.…”

Diagnosing schistosomiasis: where are we?

“…Recently, the same DNA sequence was used successfully in the detection of Schistosoma DNA in plasma by Wichmann et al 83 and in urine samples by Enk et al 84,85 and Ibironke et al 86 .…”