An epidemiological study of filariasis in Sorsogon province, Republic of the Philippines, with notes on experimental mosquito infection.

An epidemiological survey was conducted on Bancroftian filariasis in Sorsogon province, the Philippines, with special regard to low density microfilaremia (LDF). Filtration technique using nuclepore membrane examining 1 ml blood revealed 31% positive rate for microfilaria out of 262 volunteers. Out of 82 positives 21 (25.6%) had LDF (less than 10 in 1 ml blood). No conspicuous grouping of LDF was noted in younger age groups or sexes. In three out of 12 clinical filariasis, microfilaria was detected but none of them were LDF. Among 22 cases treated with diethylcarbamazine, nine subsequently had LDF suggesting necessity of improvement of drug administration regimen to avoid incomplete treatment. A series of feeding experiments using two mosquito species, Aedes poicilius and Culex quinquefasciatus, on volunteers showed that both species could act as vectors in the region. No larva was detected in either species fed on LDF carriers. It was concluded that there is little possibility that LDF plays an important role in the transmission of Bancroftian filariasis in the region.