A DIFFERENTIAL FILTRATION TECHNIQUE FOR THE MEASUREMENT OF SCHISTOSOME CERCARIAL DENSITIES IN STANDING WATERS

Abstract

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 .mu.m, allowing filtration of turbid water without clogging of the filter. A 3-level prefiltration column (1000, 500 and 200 .mu.m), 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.