Methylene blue was used as a vital stain for assessment of viability of protoscolices from hydatid cysts taking advantage of the chemical nature of the dye as a redox indicator and the kinetically distinct molecular transfer systems of Echinococcus protoscolex for uptake of materials across the tegument. To validate the criteria by which viability is assessed, control tests were performed using normal protoscolices and protoscolices previously treated with distilled water at 60 °C for 5 min. Normal protoscolices were able to adsorb and reduce the dye and have therefore lost the blue color. Protoscolices previously treated with warm water on the other hand, being functionally dead, failed to reduce the adsorbed dye and permanently retained the blue color. These findings suggest that viability of protoscolices can be assessed on the basis of acquisition and loss/ retaining of the dye blue color. Performance of methylene blue was further studied at intervals over a period of 50 min after protoscolex exposure using 1% dye concentration. Results indicated that a clear distinction between dead and alive protoscolices can be made within one min. Reading of the test after 10 min would be misleading giving a false result. It is proposed that effective assessment of protoscolex viability will reveal the relative importance of different species of intermediate hosts in parasite transmission and may as well be useful in experimental studies such as drug evaluation, immunological investigations or in vitro parasite culture. A number of studies used muscular movements and evagination as criteria for assessment of viability of protoscolices. Increasing the concentration of methylene blue to 1% was noticed to be associated with remarkable enhancement of contractility, sucker movement and evagination. Such a stimulatory action of the dye may be exploited in viability tests which adopt these criteria.
Key words: Methylene Blue, Oxygen, Protoscolices, Viability.
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