A differential filtration technique for the measurement of schistosome cercarial densities in standing waters.

The technique of differential filtration allows the detection of schistosome cercariae, with a recovery greater than 80%, in natural waters with a high concentration of microorganisms. This technique makes use of a new type of monofilament polyamide filter Nytrel-TI, with a pore size of 40 mum, allowing filtration of turbid water without clogging of the filter. A three-level prefiltration column (1000, 500 and 200 mum), which retains organisms larger than cercariae, facilitates reading of the filter. The apparatus used weighs less than 3.5 kg; it requires no power supply and can easily be used in the field.