Real-time PCR demonstrates high prevalence of Schistosoma japonicum in the Philippines: implications for surveillance and control.

Catherine A Gordon,Donald P Mcmanus,Yuesheng Li,Darren J Gray,Donald Harn,Luz P Acosta,Geoffrey N Gobert,Allen G Ross,Gail M Williams,Remigio M Olveda,Stefanie Knopp

doi:10.1371/journal.pntd.0003483

Abstract

BackgroundThe Philippines has a population of approximately 103 million people, of which 6.7 million live in schistosomiasis-endemic areas with 1.8 million people being at risk of infection with Schistosoma japonicum. Although the country-wide prevalence of schistosomiasis japonica in the Philippines is relatively low, the prevalence of schistosomiasis can be high, approaching 65% in some endemic areas. Of the currently available microscopy-based diagnostic techniques for detecting schistosome infections in the Philippines and elsewhere, most exhibit varying diagnostic performances, with the Kato-Katz (KK) method having particularly poor sensitivity for detecting low intensity infections. This suggests that the actual prevalence of schistosomiasis japonica may be much higher than previous reports have indicated.Methodology/Principal FindingsSix barangay (villages) were selected to determine the prevalence of S. japonicum in humans in the municipality of Palapag, Northern Samar. Fecal samples were collected from 560 humans and examined by the KK method and a validated real-time PCR (qPCR) assay. A high S. japonicum prevalence (90.2%) was revealed using qPCR whereas the KK method indicated a lower prevalence (22.9%). The geometric mean eggs per gram (GMEPG) determined by the qPCR was 36.5 and 11.5 by the KK. These results, particularly those obtained by the qPCR, indicate that the prevalence of schistosomiasis in this region of the Philippines is much higher than historically reported.Conclusions/SignificanceDespite being more expensive, qPCR can complement the KK procedure, particularly for surveillance and monitoring of areas where extensive schistosomiasis control has led to low prevalence and intensity infections and where schistosomiasis elimination is on the horizon, as for example in southern China.

Highlights

Schistosoma japonicum is the causative agent of intestinal schistosomiasis in the Philippines, China and parts of Indonesia
A number of molecular techniques have been used for the detection of schistosome infections including conventional PCR, real-time PCR and loop-mediated isothermal amplification (LAMP) [20,21,22,23,24,25]
Informed written consent was received from all human participants in the study and ethical approval was provided by the Ethics Committee of the Research Institute of Tropical Medicine (RITM), Manila, and the Queensland Institute of Medical Research (QIMR) Human Research Ethics Committee (Approval Number: H0309-058 (P524))

Summary

Introduction

Schistosoma japonicum is the causative agent of intestinal schistosomiasis in the Philippines, China and parts of Indonesia. Schistosomiasis is a focal disease and in some Filipino communities the prevalence of infection has been reported to be as high as 65% [5,6,7,8,9] Common diagnostic techniques, such as the microscopy-based Kato-Katz (KK) method, have been shown to have low sensitivity for detecting schistosome infections [10,11,12,13,14,15]. Of the currently available microscopy-based diagnostic techniques for detecting schistosome infections in the Philippines and elsewhere, most exhibit varying diagnostic performances, with the Kato-Katz (KK) method having poor sensitivity for detecting low intensity infections This suggests that the actual prevalence of schistosomiasis japonica may be much higher than previous reports have indicated

Methods

Results

Conclusion