Bancroftian filariasis and membrane filters: are night surveys necessary?

Paired day and night blood specimens from 41 persons living in a hyperendemic Wuchereria bancrofti area of southwestern Ethiopia were examined for microfilariae by Nuclepore filter, thick film, and counting chamber techniques. Filtering techniques were so highly sensitive that more infected persons were identified by filtering day blood than by examining night blood by conventional methods. Increasing the volume of blood filtered from 1 ml to 5 ml increased the number of positives identified during the day. Filtering 5 ml of day blood obviated the need for examining night blood, even though a high proportion of infected persons had very low numbers of circulating microfilariae.