A field survey on the role of low-density microfilaraemia cases in the transmission of filariasis
Li, Z.X.; Shi, Z.J.
Southeast Asian Journal of Tropical Medicine and Public Health 20(1): 153-156
1989
ISSN/ISBN: 0125-1562 PMID: 2772701 Document Number: 339666
In former filariasis endemic areas, where the disease has been basically controlled, a few cases of low-density microfilaraemia remain. A survey was carried out in Deqing County, Zhejiang Province, from September 1981 to 1986 in order to determine whether such cases play a role in the continuation of transmission. The results of parasitological and entomological investigations for two consecutive years revealed that after the implementation of intervention measures, the mean microfilaraemia rate in the population fell to about 0.5% and the mean microfilaria density to about 4.2 mf/60 .mu.l of blood in previously endemic areas of malayan filariasis. Although there were considerable numbers of Anopheles sinensis biting humans, infective larvae could be found in only two positive mosquitoes out of 5,484 dissected, and no new microfilaraemic cases were detected in the 1983 and 1986 follow-up blood examinations, indicating that transmission had already been interrupted. Two volunteers with a microfilaraemia of 3-5 mf/60 .mu.l of blood were exposed to two batches of An. sinensis in August 1981. The engorged mosquitoes were dissected eight days later. Even though the infection rate of An. sinensis having fed on low-density microfilaraemic cases was as high as 16.8%, the intensity of infection was extremely low, being 1.1 mf/mosquito. From the transmission dynamics point of view, infected mosquitoes carrying very few infective larvae have no practical significance in the transmisssion of filariasis. It is suggested that the treatment of persons with low-density microfilaraemia (with 5 mf/60 .mu.l of blood) in areas with low microfilaria rates (< 1%) need not to be considered as essential.