Bancroftian filariasis: a comparison of microfilariae counting techniques using counting chamber, standard slide and membrane (nuclepore) filtration.

Three techniques were compared for counting microfilariae of Wuchereria bancrofti in blood specimens--a standard slide method, the counting chamber technique (CCT) and a membrane filtration technique (MFCT). The CCT was much more sensitive than the slide method, the difference in sensitivity between these two methods probably being due mainly to the loss of microfilariae during the dehaemoglobinizing process prior to staining in the standard slide method. There was good correlation between the techniques when 0.1 ml of finger-prick blood was examined by the CCT and 1 ml of venous blood by the MFCT. The number of additional positives revealed by the MFCT was ten of 275 (3.6%) subjects examined. The use of venepuncture for MFCT is impractical for field surveys in East Africa whereas a microfilarial count on 0.1 ml of finger-prick blood meets most of the criteria required of a field technique. The method is simple, quantitative and acceptable to the population. The results are reproducible, can be readily checked, the technique provides a useful and practical method for obtaining prevalence information following control schemes. The finding of a relatively low prevalence of microfilariae seen by both MFCT and CCT in children aged five to nine years from a highly endemic filariasis area agrees with the results of previous East African surveys carried out by blood smear and CCT.