A polymerase chain reaction assay for the survey of bancroftian filariasis

Abstract

A polymerase chain reaction (PCR) assay based on a highly repeated DNA sequence found in Wuchereria bancrofti (SspI repeat) has been modified for the survey of bancroftian filariasis in expatriate workers (Myamese, Karen and Mon) from Myanmar where human filariasis is endemic. The PCR was very sensitive with the ability to detect the presence of as little as 10 pg of parasite DNA. The primers used in this PCR also showed highly specific amplification of parasite DNA without the presence of non-specific and non-target PCR products such as Brugia malayi, Plasmodium falciparum and human DNA. The primers were used to investigate filariasis in four provinces in the central and western Thailand, Samut Songkram, Ratchaburi, Nakhon Pathom and Tak during 1997-2001. Among them, Tak and Ratchaburi are the only endemic areas of bancroftian filariasis. In this field study, 1,299 human blood samples (501 from Samut Songkram, 510 from Ratchaburi, 109 from Nakhon Pathom, and 179 from Tak) were collected and screened by PCR. The result showed that 1, 2, 3, and 33 patients from Samut Songkram, Ratchaburi, Nakhon Pathom, and Tak respectively were infected with W. bancrofti. These numbers were corresponded to the prevalence rate of infection of 0.2, 0.4, 2.8, and 18.5%, respectively. The PCR was able to detect the third-stage infectious larvae (L3) from Culex quinquefasciatus, mosquito vector of the W. bancrofti, that was experimentally fed to infected patient. The PCR screening of each of field mosquito pools from two endemic areas, Ratchaburi and Tak, showed that no L3 of W. bancrofti was detected.