Comparison of methods for diagnosis of bancroftian filariasis

Abstract

OBJECTIVE: Evaluate a rapid format immuno-chromatographic card test (ICT Diagnostics, Australia) in the diagnosis of bancroftian filariasis. METHOD: Thick night blood films (TBF), Nuclepore membrane filtration (NMF) and ICT were performed on venous blood collected from 226 individuals selected from highly endemic localities in Colombo [n~153 (63%)] and Gampaha [n=73 (32.3%)] districts. Blood was collected between 20.00 and 23.00 hours. 60ul of non-heparinised blood, 1ml and lOOpl of heparinised blood were used in TBF, NMF and ICT tests respectively. A self-administered questionnaire (expert validated) was used to screen for clinical manifestations. RESULTS: The mean age of the study population was 34-8yrs (range 14-76, SD 16.78); the male: female ratio was 98: 128. NMF was positive in 66/226 (29%), with a mean microfilariae count of 343/ml (range 9-1782, SD 422). All 66 were positive by ICT (sensitivity = 100%) but only 63 by TBF (sen.sitivity=95%). 59/226 (26.1%) had one or more filariasis specific symptoms (lymphoedema, hydrocoele, lymphadenitis, lymphangitis, fever, night cough and red spots). Of the 59, 25 (42.3%) were positive by the ICT, 24 (40.6%) were positive by NMF. The other 34 were negative in both tests. Out of the 166 asymptomatics, 42 were positive in both NMF and ICT, but there were 13 more positives with ICT. CONCLUSIONS: ICT card test was more sensitive in detecting microfilaria compared to venous thick night blood film. Both ICT and NMF were positive in only in about 40% of individuals with symptoms suggestive of filariasis.