UNEXPECTEDLY HIGH PREVALENCE OF WUCHERERIA BANCROFTI INFECTION OBTAINED BY ICT CARD TESTS IN COMPARISON WITH THAT DETERMINED BY IgG4 ELISA USING URINE SAMPLES : A POSSIBILITY OF FALSE POSITIVE REACTIONS WITH ICT CARD TESTS IN A STUDY IN THAILAND

Abstract

With the purposes of studying the recent prevalence of Wuchereria bancrofti infection in Thai-Myanmar border areas, and evaluating the usefulness of a new ELISA, which uses urine as samples (urine ELISA), 519 people in Sangkhla Buri and 84 people in Suan Phung were examined by ICT card test for filarial antigen and by urine ELISA for filaria-specific IgG4. In the former area, positive rates by ICT test and the ELISA were 16.8% and 21.2%, respectively; in the latter area, the respective rates were 10.7% and 7.1%. These figures were unexpected, because the urine ELISA used to give much higher prevalence than antigenemia tests in our previous studies. In addition, only 37 of 96 ICT positives (38.5%) were urine ELISA positive. Our previous studies showed that the sensitivity of urine ELISA among the microfilaria and/or antigen positive individuals was more than 90%. Diethylcarbamazine treatment given to the known ICT positives at 300 mg/day for 12 days reduced antigenemia rate from 100% to 32.8%, which was determined 2 months after treatment by Og4C3 ELISA. The reduction of 67.2% seemed to be unusually high. These conflicting results could be explained by possible false positive reactions produced by ICT test.