Research Article: Real-time PCR Demonstrates High Prevalence of Schistosoma japonicum in the Philippines: Implications for Surveillance and Control

Date Published: January 21, 2015

Publisher: Public Library of Science

Author(s): Catherine. A. Gordon, Luz P. Acosta, Geoffrey N. Gobert, Remigio M. Olveda, Allen G. Ross, Gail M. Williams, Darren J. Gray, Donald Harn, Yuesheng Li, Donald P. McManus, Stefanie Knopp.

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.

Partial Text: Schistosoma japonicum is the causative agent of intestinal schistosomiasis in the Philippines, China and parts of Indonesia. In the Philippines, 10 out of 16 regions have reported cases of schistosomiasis, with an estimated 6.7 million people living in endemic areas [1]. Of these, 1.8 million, nearly 2% of the total Philippine population (105 million) [2], are considered to be directly exposed to infection through farming, fishing and other essential occupational and domestic activities involving regular water contact [3,4]. The spread of schistosomiasis japonica requires the presence of the intermediate aquatic snail host, Oncomelania hupensis quadrasi, appropriate mammalian definitive hosts and specific environmental conditions to support transmission. Schistosomiasis is a focal disease and in some Filipino communities the prevalence of infection has been reported to be as high as 65% [5–9].

In this study we found a high prevalence of schistosomiasis japonica in humans in the municipality of Palapag in Northern Samar province, the Philippines—higher than previously reported for this region. The high prevalence of S. japonicum mirrored the results of a small pilot study we undertook in September 2010 in Western Samar [26]. The prevalence (90.2%) and infection intensity (36.5 qGMEPG) values determined by the qPCR assay in this study were considerably higher than those obtained using the KK method (22.9%; 11.5 GMEPG). The sensitivity of the KK technique was estimated as 26.1% and the specificity as 82.8%. It is noteworthy that the KK sensitivity calculated in this study was from individuals submitting two stool samples, with three slides per stool only. The disparity between the two methods used in the current study clearly highlights the need for the development of a more sensitive technique for detecting schistosome infections in humans. The majority (N = 345, 61.61%) of qPCR positive samples were low intensity infections.

The results presented here clearly indicate that the prevalence of S. japonicum in Palapag, Northern Samar is much higher than has previously been reported, a situation that may be reflected in other endemic areas in the Philippines. Through diagnostic surveillance, molecular tools such as qPCR can provide improved assessment of the effectiveness and impact of integrated schistosomiasis control strategies.



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