A field survey on the role of low-density microfilaraemia cases in the transmission of filariasis.

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 microliter of blood in previously endemic areas of malayan filariasis. Although there were considerable numbers of An. 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 microliter of blood were exposed to two batches of An. sinesis 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 transmission of filariasis. It is suggested that the treatment of persons with low-density microfilaraemia (with 5 mf/60 microliters of blood) in areas with low microfilaria rates (less than 1%) need not to be considered as essential.

Clinical trial on furapyrimidone in filariasis.

A clinical trial was carried out with furapyrimidone in treating 51 patients with B. malayi, 159 with W. bancrofti and eight with D. perstans using different dosage schedules. Two hundred and fifty-seven cases of Malayan and bancroftian filariasis were treated with hetrazan for comparison. The results based on the microfilaricidal effects suggest that furapyrimidone possesses similar therapeutic effects of hetrazan on Malayan filariasis at eight-month follow-up, and higher incidences of microfilarial disappearance of W. bancrofti infection (81.3%) at six-month follow-up. The drug was also effective against D. perstans. The side effects consisted of fever and irritation of the digestive tract. Fever may be related to allergic reaction of foreign protein from the dead or dying parasites. The side reactions are similar to those of hetrazan and usually not serious. Comparing the efficacies and side effects of furapyrimidone with different dosage schedules the authors recommend regimens of 15 to 20 mg/kg/day for six days in treating Malayan filariasis and 20 mg/kg/day for seven days in treating bancroftian filariasis.