Effect of anthelmintics on the early stage of Enterobius vermicularis
Seung-Yull Cho,Shin Yong Kang,Suk Il Kim and Chul Yong Song*
Department of Parasitology, College of Medicine, Chung-Ang University, Seoul 151, Korea.
*Department of Biology, College of Liberal Arts and Science, Chung-Ang University, Seoul 151, Korea.
In order to determine the susceptible age of Enterobius vermicularis to anthelmintics and to observe the chronologic growth of female E. vermicularis in man, experimental infections were done. About 500 eggs were challenged to 19 volunteers. After 4, 8, 16, 20, 24, 28, 32 and 35 days of infection, each case was treated by either mebendazole or pyrantel pamoate. On the 40th day of infection all cases including control were treated again to terminate the expermental infection and to evaluate the effect of previous treatment. Each case collected 3-day stools to harvest the expelled worms. The results could be summarized as follows: The infection rates of females were in range of 0.6-13.1% in control cases. Because the collected worms showed comparable growth and development by day, the worns were concluded to be derived from experimental infection. Cases that were treated with mebendazole on 4, 8 and 16 days after infection expelled 37.5%, 2.5% and 67.5% of the number expelled by a control case on the 40th day. Cases treated thereafter expelled no worms on the 40 days. Cases that were treated with pyrantel pamoates on 4, 8, 16, 24, 28, 32 and 35 days, expelled 90.7%, 25%, 45.3%, 8%, 2.7%, 5% and 29.3% of the number collected from control cases in respect. All the worms collected were females. The total body length increased consistently and comparably from the 20th day of infection. Those collected on the 20th day were 2.5-3.0 mm long with vigina, sac-like structure and strands of ovaries; 24 day-old worms may have short uterus, 28 day-old worms had long uterus without eggs, 32 day-old worms began to produce eggs, 35 day-old worms showed wide variations in egg deposit in uterus, and 40 day-old worms had uterus filled with eggs from vulva to anal levels. From the above results, it was inferred that the life span of female Enterobius vermicularis was longer than 40 days, and the developmental stages of worms younger than 16 days resisted considerably to both mebendazole and pyrantel pamoate.
Fig. 1 Mean and standard deviation of total body length of female E. vermicularis collected on 20-40 days after the experimental infection. Length on the 0th day was that of naturally hatched larva from the shell (0.173mm in average).
Fig. 2 Degree of drug resistance according to age of infection in Enterobius vermicularis. The degree of resistance was calculated by the formula: (No. recovered in 2nd treatment on 40th day / Mean No. from control cases)×100
Table 1 Results of the first experiment in volunteers
Table 2 Results of the second experiment in volunteers
Table 3 Distribution of female Enterobius vermicularis by total body length which were collected on different days after the experimental infection. Out of 490 worms collected, 411 were measured
Table 4 Total body length of female E. vermicularis (mean, standard deviation and range) as presented by infection day and by individual case
Table 5 Developmental status of uterus in E. vermicularis by infection day
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