Comparison of different staining methods for determination of viability on Mesocestoides vogae tetrathyridia

Mesocestoides vogae is widely employed as a model for studying the biology, differentiation, and experimental chemotherapy of cestodes. Currently, there are few techniques to measure the viability of M. vogae metacestodes during pharmacological experiments. The aim of the present work was to evaluate and compare different staining techniques to determine objectively the viability of M. vogae tetrathyridia. Eosin (0.05% w/v), methylene blue (0.01% w/v), propidium iodide (PI, 2 μg/ml), and fluorescein diacetate (FDA, 0.5 μg/ml) solutions were tested against live, heat-killed (cultivated at 65 °C for 2 h) and thymol-treated tetrathyridia (50 and 250 μg/ml). Parasites were counted under a dissecting microscope or a fluorescence compound microscope, as appropriate. Studies by scanning electron microscope were performed to compare the ultrastructural damage with the viability of parasites. After comparing the performance of different dyes, we chose the eosin staining technique because its simplicity, rapidity, sensitivity, low cost and fidelity.