Evaluation of a membrane (Nuclepore) filtration method using capillary blood for the detection of microfilariae

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Abstract
The efficacy of a membrane (Nuclepore) filtration technique using capillary blood (100 mm2) for the detection of blood-circulating microfilariae was investigated during a prevalence survey for Wuchereria bancrofti and Mansonetta ozzardi in north Trinidad by comparing results thus obtained with results from conventional thick smear preparations (25 mm3) and from membrane (Nuclepore) filtration of venous blood (1 ml). Prevalence rates of W. bancrofti were 14% by thick smear, 17% by filtration of capillary blood and 16% by filtration of venous blood. For M. ozzardi the corresponding rates were 27%, 29% and 31%. A total of 389 persons was examined by all three methods. Microfilaria detection rates for both of the filtration techniques were significantly higher than by thick smear preparation, with the exception of results for M. ozzardi obtained by filtration of capillary blood. There was no significant difference between the number of positive persons detected by filtration of capillary blood and filtration of venous blood. Significantly higher microfilaria densities per unit volume of blood were recorded by thick smear preparation and filtration of capillary blood than by filtration of venous blood, whereas results for the two capillary blood techniques were similar. In the detection of low density microfilaraemias, membrane filtration of capillary blood provides a practical and sensitive alternative to venous blood filtration and has the additional advantage of capillary blood collection rather than venepuncture.