Development of an in vitro drug sensitivity assay for Trichuris muris first-stage larvae

BACKGROUND: Trichuriasis represents a major public health problem in the developing world and is regarded as a neglected disease. Albendazole and mebendazole, the two drugs of choice against trichuriasis display only moderate cure rates, hence alternative drugs are needed. To identify candidate compounds, in vitro drug sensitivity testing currently relies on the adult Trichuris muris motility assay. The objective of the present study was to develop a simple and cost-effective drug sensitivity assay using Trichuris muris first-stage larvae (L1). METHODS: Several potential triggers that induce hatching of T. muris were studied, including gastrointestinal enzymes, acidic environment and intestinal microflora. Next, optimal culture conditions for T. muris L1 were determined assessing a wide range of culture media. T. muris L1 were incubated in the presence of mebendazole, ivermectin, nitazoxanide, levamisole or oxantel pamoate at 37°C. The viability of the parasites was evaluated microscopically after 24 hours. The usefulness of fluorescent markers (resazurin, calcein AM, ethidium homodimer-1 or fluorescein-conjugated albumin) in drug sensitivity testing was also assessed. RESULTS: The established L1 motility assay provided accurate and reproducible drug effect data in vitro. IC(50) values for oxantel pamoate, levamisole and nitazoxanide were 0.05, 1.75 and 4.43 μg/mL, respectively. Mebendazole and ivermectin failed to show any trichuricidal effect on L1. No correlation was found between data from the four fluorescent markers and the comparative motility assay. CONCLUSIONS: The motility assay based on L1 was found suitable for drug sensitivity screening. It is rather simple, cost-effective, time-saving and sustains medium-throughput testing. Furthermore, it greatly reduces the need for the animal host and is therefore more ethical. None of the viability markers assessed in this study were found to be satisfactory.