STUDIES ON THE PERIODICITY AND INTRAVASCULAR DISTRIBUTION OF WUCHERERIA-BANCROFTI MICROFILARIAE IN PAIRED SAMPLES OF CAPILLARY AND VENOUS-BLOOD FROM RECIFE, BRAZIL

We examined the periodicity and intravascular distribution of Wucherer ia bancrofti microfilariae (mf) and determined the effect of these par asite properties on the accuracy of blood filming and filtration metho ds for diagnosis of bancroftian filariasis in the endemic area of Reci fe, Brazil. Microfilariae in both venous and capillary blood exhibited a nocturnal periodicity pattern with a relatively high amplitude. Ove rall, capillary blood contained similar to 1-25 times the number of mf present at the same time in the same volume of venous blood. However, the ratio of mf present in capillary and venous blood varied over a 2 4-hour period, so that the fewest mf were present in the capillary bed of the skin at the time when biting activity of the local Culex vecto r is the lowest. Twenty or 60 mu l blood films did not reliably detect carriers with fewer than 100 or 60 mf/ml venous blood, respectively, and were thus inadequate for the identification of low density mf carr iers. In contrast, all carriers with >1 mf/20 or 60 mu l blood smear a t night could be identified during daytime hours by filtration of 1 ml venous blood.