The non-randomness of the distribution of Trichuris trichiura and Ascaris lumbricoides eggs in faeces and the effect of stirring faecal specimens

Abstract

Experiments were performed to describe the distribution of Trichuris trichiura and Ascaris lumbricoides eggs in faeces and to test for the effect of stirring faecal specimens prior to sampling. For each of 5 volunteers infected with A. lumbricoides and 7 volunteers infected with T. trichiura, helminth eggs were counted in 150 samples from a single stool specimen using the Kato-Katz smear technique. No significant differences between the distribution of eggs in samples from the surface and the centre of the specimens were found. Prior to stirring, eggs were found to be aggregately distributed in four of the specimens with T. trichiura and all of the specimens with A. lumbricoides. The distributions of eggs were not significantly altered by stirring the stool prior to sampling except in the case of one volunteer infected with A. lumbricoides for whom stirring reduced variability.