A polymerase chain reaction-based assay for detection of Wuchereria bancrofti in human blood and Culex pipiens

Human blood samples and indoor-resting Culex pipiens were collected in 33 randomly selected houses from different sectors of a village in the Nile Delta of Egypt which was endemic for Wuchereria bancrofti. Blood was also collected from subjects with no history of living in filarial endemic areas. Human blood samples were divided and assessed by both membrane filtration and polymerase chain reaction (PCR). Similarly, mosquito samples were assessed by both dissection and PCR. Blood pools representing each household were tested by PCR. If a pool gave a positive result, then individual blood specimens were also tested by PCR. Of the 33 houses tested, both membrane filtration and blood pools assayed by PCR identified 14 (42.4%) 'infected houses'. PCR detected parasite deoxyribonucleic acid (DNA) in blood pools from an additional 3 households that gave negative results by membrane filtration. Of 178 endemic blood samples tested by membrane filtration, 22 (12.3%) had microfilariae and all were individually positive by PCR. Although microfilaria counts were lower in blood collected during the day than in night-collected blood, the PCR results were consistent, regardless of time of collection. All non-endemic blood samples were negative by PCR. Among the 33 houses tested, mosquito pools assayed by PCR identified 17 (51.5%) as 'infected households'. Of these, 8 houses (47%) contained at least one microfilaraemic resident. One 'infected household' was identified by mosquito dissection. We concluded that PCR is a powerful epidemiological tool for screening villages for the prevalence of W. bancrofti. PCR detection of W. bancrofti DNA in blood-fed mosquitoes could be used initially to locate endemic areas with transmission of bancroftian filariasis. PCR detection of W. bancrofti DNA in blood collected during the day could then be used to assess W. bancrofti infection rates.