Assessment of in vitro killing assays for detecting praziquantel-induced death in Posthodiplostomum minimum metacercariae

- Fish intermediate hosts harbor trematode metacercariae that are infectious for vertebrates.
- In some systems, praziquantel treatment of fish may aid in disrupting parasite life cycles.
- Few in vitro tests are available to compare the drug sensitivity of metacercariae recovered from fish.
- Propidium iodide staining was a suitable method for detecting praziquantel-mediated death of metacerariae in vitro.

Control of parasitic infections may be achieved by eliminating developmental stages present within intermediate hosts, thereby disrupting the parasite life cycle. For several trematodes relevant to human and veterinary medicine, this involves targeting the metacercarial stage found in fish intermediate hosts. Treatment of fish with praziquantel is one potential approach for targeting the metacercaria stage. To date, studies investigating praziquantel-induced metacercarial death in fish rely on counting parasites and visually assessing morphology or movement. In this study, we investigate quantitative methods for detecting praziquantel-induced death using a Posthodiplostomum minimum model. Our results revealed that propidium iodide staining accurately identified praziquantel-induced death and the level of staining was proportional to the concentration of praziquantel. In contrast, detection of ATP, resazurin metabolism, and trypan blue staining were poor indicators of metacercarial death. The propidium iodide method offers an advantage over simple visualization of parasite movement and could be used to determine EC50 values relevant for comparison of praziquantel sensitivity or resistance.

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