PCR diagnosis of Opisthorchis viverrini and Haplorchis taichui infections in an endemic Lao community: a comparison of diagnostic methods for parasitological field surveys

Opisthorchiasis is a major public health problem in Southeast Asia. Affected individuals often have mixed infections with the liver fluke Opisthorchis viverrini and minute intestinal flukes such as Haplorchis taichui. The usual methods of diagnosing these infections involve the demonstration of fluke eggs in stool samples under light microscopy, but sensitivity and specificity are low.

We developed two PCR tests that detect and discriminate between O. viverrini and H. taichui infections. PCR tests were validated by stool samples from purged individuals. We then applied the PCR tests to estimate the prevalence of O. viverrini and H. taichui infections from a random sample of individuals selected from an endemic community in Khong District, Laos. PCR results were compared with those from the Kato-Katz (KK) method and the formalin-ether concentration technique (FECT).

When validated with purge results, PCR tests of O. viverrini and H. taichui had a sensitivity of 93.7% (95% Confidence Interval (CI): 85.8 to 97.9%) and 73.3% (95% CI: 60.3 to 83.9%) and could detect as low as 0.75 pg DNA and 1.32 ng DNA, respectively. The PCR-determined community prevalence of O. viverrini and H. taichui infections was 63.9% (95% CI: 54.1 to 72.9%) and 30.6% (95% CI: 22.1 to 40.2%), respectively. Using PCR as the gold standard to detect O. viverrini, three KK thick smears performed comparably well whereas one KK smear and FECT were poorer (sensitivity of 91.4% (95% CI: 81.0 to 97.1%), 62.3% (95% CI: 49.8 to 73.7%) and 49.3% (95% CI: 37.0 to 61.6%), respectively).

PCR may be a valuable and sensitive diagnostic tool, particularly for low intensity O. viverrini and H. taichui infections.