Evaluation of a PCR-ELISA to detect Wuchereria bancrofti in Culex pipiens from an Egyptian village with a low prevalence of filariasis

Abstract

The programmes for the elimination of bancroftian filariasis that have been implemented in the Nile delta of Egypt are expected to lead to substantial reductions in filarial loads in the treated populations. Better methods than those currently available are needed for monitoring the efficacy of these and similar efforts at intervention. A PCR-ELISA was therefore evaluated as an epidemiological tool for the detection of the Wuchereria-bancrofti-specific SspI repeat in pools of Culex pipiens collected in a village with a low prevalence of filarial infection in its human residents (2.1%). Indoor-resting mosquitoes were collected by aspiration from 114 randomly selected houses (during one to nine visits/house) and separated into 673 pools, each of which held the mosquitoes collected during one night from one house. Although 18 (2.7%) of the pools showed PCR inhibition and had to be excluded, filarial DNA was detected, using the PCR-ELISA, in 91 (13.9%) of the 655 remaining mosquito pools. The minimum prevalence of W. bancrofti infection in the mosquitoes caught (assuming one infected mosquito/positive pool) was 2.8%. The mean (s.d.) number of mosquitoes/pool did not vary significantly between positive [5.5 (3.4)] and negative [4.9 (3.5)] pools. The assay detected parasite DNA in mosquitoes from 19.3% of 114 houses when only the first visit was considered and from 73.9% of the 88 houses visited more than once. The PCR-ELISA yielded results comparable with those of the regular PCR-SspI assay. The latter assay is recommended for the routine examination, in laboratories in endemic areas, of mosquito pools from randomly selected houses, as the ELISA component of the PCR-ELISA is exceedingly time-consuming, expensive and requires special equipment.