Hyperendemic Bancroftian Filariasis in the Kingdom of Tonga: The Application of the Membrane Filter Concentration Technique to an Age-Stratified Blood Survey *

Abstract

A survey carried out in Tonga, an area of hyperendemic subperiodic Wuchereria bancrofti filariasis, compared the diagnostic efficiency of the membrane-filtration and stained blood film techniques. Membrane filter concentration of 1 ml blood revealed a microfilaria rate that was approximately the same for all age groups, from 5 to 9 years old to > 50 years old, about 70%. The microfilaria rate by examination of stained 60 mm3 thick blood films was lower for all age groups. Membrane filter concentration detected 7.8 times as many infections as thick film diagnosis in the 5- to 9-year-old group, 4.8 times in the 10- to 14-year-old group, 2.4 times in the 15- to 20- and 21- to 50-year-old groups, and 1.6 times in the >50-year-old group. Concentration revealed the presence of microfilariae in the blood of 5 of 8 patients with gross elephantiasis, whereas microfilariae were found in the stained thick-film of only 1 of these individuals.