Detection of Wuchereria bancrofti in mosquitoes by the polymerase chain reaction: a potentially useful tool for large-scale control programmes

Focally endemic bancroftian filariasis is targeted for elimination in the N ile delta of Egypt. Improved methods are needed for identifying endemic vil lages to be included in the control programme and for monitoring its succes s. We have evaluated the performance of a polymerase chain reaction (PCR) a ssay in estimating Wuchereria bancrofti infection in pools of Culex pipiens (1-25 females) from 2 adjacent villages with high (El Qolzom, 10.8%) and l ow (Kafr Shorafa, 2.1%) prevalence rates of human filariasis. This assay de tects a repeated sequence in W bancrofti deoxyribonucleic acid (DNA). Mosqu itoes resting within houses were captured by aspiration and pooled by house . Houses were classified as positive or negative for human filarial infecti on based on night blood examinations of residents. The assay detected paras ite DNA in mosquitoes from 60% of 25 infected houses and 24% of 25 uninfect ed houses. PCR processing of mosquitoes caught within houses of unknown fil ariasis infection status (44 in El Qolzom, 37 in Kafr Shorafa) identified 3 1.8% and 8.1% of houses, respectively, as containing infected mosquitoes. T hese results support the validity of the PCR assay for evaluating filarial prevalence in different villages. C. pipiens collected outdoors in dry ice- baited traps and tested by PCR (266 in Qolzom, 82 in Kafr Shorafa) did not contain parasite DNA. Pools of female mosquitoes (296 in Qolzom 240 in Kafr Shorafa) captured in oviposition traps were also negative. We concluded th at the PCR based assay is a powerful epidemiological tool that can be used for evaluating W. bancrofti infection in villages in the Nile delta and for monitoring the application of control programmes in filariasis endemic are as.