Tropical medicine and health · 2026
Diagnostic accuracy of ARK Checker® C/G-DyLight® 488: simultaneous detection of Giardia and Cryptosporidium by fluorescent antibody microscopy.
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Oshiro Yusuke, Kawashima Akira, Akashi Megumi, Yanagawa Yasuaki, Shimodaira Kanako, Matsuzawa Haruka, Nemoto Takashi, Shimogawara Rieko, Kurokawa Masami, Ando Naokatsu, Uemura Haruka, Aoki Takahiro, Yamamoto Kei, Akiyama Junichi, Mizushima Daisuke, Kitazawa Toshio, Gatanaga Hiroyuki, Yagita Kenji, Watanabe Koji
Аннотация
BACKGROUND: Giardiasis and cryptosporidiosis are often misdiagnosed by stool ova and parasite test (classical O&P). Multiplex PCR and rapid antigen immunochromatography (rapid-IC) could offer high diagnostic accuracy; however, their cost and restricted coverage, especially for parasites, limit routine use. This study evaluated the efficacy of adapted fluorescent antibody microscopy using ARK Checker® C/G-DyLight® 488 (FAM-TEST). The reagent is a liquid-form conjugated antibodies which directly detect Giardia cysts and Cryptosporidium oocysts under fluorescence microscopy.
METHODS: A total of 694 stool samples submitted for microbiological examination were screened by FAM-TEST, in which specimens were mixed with DyLight-488-labeled antibodies and examined microscopically. Samples with discordant results among these methods were additionally tested by conventional PCR with Sanger sequencing to verify infection status.
RESULTS: Diagnostic accuracy was assessed by reference to multiplex PCR results and compared with that of rapid-IC. FAM-TEST identified Giardia and/or Cryptosporidium in 35 samples. In addition, 49 FAM-TEST-negative samples from a randomly selected month were included as negative controls. For Giardia, all FAM-TEST results were identical to those of rapid-IC, including three false negatives [88.0% sensitivity, 100% specificity, 100% positive predictive value (PPV), and 95.2% negative predictive value (NPV)]. For Cryptosporidium, FAM-TEST showed 93.8% sensitivity, 100% specificity, 100% PPV, and 98.6% NPV, which were comparable with those of rapid-IC. Notably, conventional PCR for Giardia sequences produced negative results for three samples considered to yield FAM-TEST false negatives, raising another possibility of multiplex PCR false positives or extremely low pathogen burden.
CONCLUSION: Concurrent use of FAM-TEST with classical O&P offers a cost-effective, practical diagnostic approach for enteric parasites, which especially strengthens diagnostic accuracy for giardiasis/cryptosporidiosis.
METHODS: A total of 694 stool samples submitted for microbiological examination were screened by FAM-TEST, in which specimens were mixed with DyLight-488-labeled antibodies and examined microscopically. Samples with discordant results among these methods were additionally tested by conventional PCR with Sanger sequencing to verify infection status.
RESULTS: Diagnostic accuracy was assessed by reference to multiplex PCR results and compared with that of rapid-IC. FAM-TEST identified Giardia and/or Cryptosporidium in 35 samples. In addition, 49 FAM-TEST-negative samples from a randomly selected month were included as negative controls. For Giardia, all FAM-TEST results were identical to those of rapid-IC, including three false negatives [88.0% sensitivity, 100% specificity, 100% positive predictive value (PPV), and 95.2% negative predictive value (NPV)]. For Cryptosporidium, FAM-TEST showed 93.8% sensitivity, 100% specificity, 100% PPV, and 98.6% NPV, which were comparable with those of rapid-IC. Notably, conventional PCR for Giardia sequences produced negative results for three samples considered to yield FAM-TEST false negatives, raising another possibility of multiplex PCR false positives or extremely low pathogen burden.
CONCLUSION: Concurrent use of FAM-TEST with classical O&P offers a cost-effective, practical diagnostic approach for enteric parasites, which especially strengthens diagnostic accuracy for giardiasis/cryptosporidiosis.