Hyperendemic bancroftian filariasis in the Kingdom of Tonga: the application of the membrane filter concentration technique to an age-stratified blood survey.

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 greater than 50 years old, about 70%. The microfilaria rate by examination of stained 60 mm-3 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 20- and 21- to 50-year-old groups, and 1.6 times in the greater than 50-year-old group. Concentration revealed the prsence 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.