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Background <p>Giardiasis and cryptosporidiosis are often misdiagnosed by stool ova and parasite test (classical O&amp;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 <i>Giardia</i> cysts and <i>Cryptosporidium</i> oocysts under fluorescence microscopy.</p> Methods <p>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.</p> Results <p>Diagnostic accuracy was assessed by reference to multiplex PCR results and compared with that of rapid-IC. FAM-TEST identified <i>Giardia</i> and/or <i>Cryptosporidium</i> in 35 samples. In addition, 49 FAM-TEST-negative samples from a randomly selected month were included as negative controls. For <i>Giardia</i>, 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 <i>Cryptosporidium</i>, 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 <i>Giardia</i> 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.</p> Conclusion <p>Concurrent use of FAM-TEST with classical O&amp;P offers a cost-effective, practical diagnostic approach for enteric parasites, which especially strengthens diagnostic accuracy for giardiasis/cryptosporidiosis.</p>

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Diagnostic accuracy of ARK Checker® C/G–DyLight® 488: simultaneous detection of Giardia and Cryptosporidium by fluorescent antibody microscopy

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月27日

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  • Yusuke Oshiro,
  • Akira Kawashima,
  • Megumi Akashi,
  • Yasuaki Yanagawa,
  • Kanako Shimodaira,
  • Haruka Matsuzawa,
  • Takashi Nemoto,
  • Rieko Shimogawara,
  • Masami Kurokawa,
  • Naokatsu Ando,
  • Haruka Uemura,
  • Takahiro Aoki,
  • Kei Yamamoto,
  • Junichi Akiyama,
  • Daisuke Mizushima,
  • Toshio Kitazawa,
  • Hiroyuki Gatanaga,
  • Kenji Yagita,
  • Koji Watanabe

摘要

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.