Population dynamics of human helminth infections: control by chemotherapy

Epidemiological Studies On Ascaris Lumbricoides Reinfection In Rural Communities In Korea: 1. The Relationship Between Prevalence And Monthly Reinfection Rate

The epidemiological relationship between the current prevalence and monthly reinfection rate of Ascaris lumbricoides was observed in rural communities in Korea by measns of blanket mass chemotherapy and worm collection for measurement of the prevalence and reinfection rates. During the period from 1975 to 1980, a total of 4,466 inhabitants in 10 different localities were treated with 10 mg/kg of pyrantel pamoate and 2 days' whole stools were collected from 2,547 inhabitants. The stools were examined for the presence of expelled adult and/or young worms, which represent the prevalence and reinfection rates for past 2 months respectively. After then, the obtained rates were correlated each other applying the time-prevalence curve proposed by Hayashi. It was observed that the prevalence (overall worm positive rate) and worm burden per individual ranged by areas from 13.6 to 72.3% and 1.4~10.2 respectively. The calculated monthly reinfection rates (X) (from young worm positive rates) according to areas were in the range, 2.6~16.2%, and clearly correlated with the current prevalence (Y) under the equation, Y=1-(1-X)(7.2) where 7.2 is time in month. The equation means that after one time mass chemotherapy the period needed to attain equilibrium of prevalence again would be about 7~8 months. And it is inferred that the majority of reinfected worms in human host turn over every 7~8 months.

Epidemiological Studies On Ascaris Lumbricoides Reinfection In Rural Communities In Korea II. Age-Specific Reinfection Rates And Familial Aggregation Of The Reinfected Cases

Epidemiological studies on the reinfection pattern of Ascaris lumbricoides were undertaken by means of blanket mass chemotherapy and worm collection in a rural village in Korea, during 1977~1980. The study objectives were to determine the age(sex)-specific reinfection rate during 2, 4, 6 and 12 months through repeated mass chemotherapy with pyrantel pamoate, and to observe the familial aggregation tendency of the reinfected cases. The results obtained are as follows: 1. The age(sex)-reinfection curve revealed that the reinfection rate is much higher in younger individuals than in olders in all of 4 kinds of interval chemotherapy groups. The highest reinfection rate and the highest burden of reinfected worms were observed in preschool childen, followed by primary school students. Such fluctuation in the age-specific reinfection rates was more pronounced in males than in females. 2. There was noted a significant tendency of familial aggregation among the reinfected cases. It is suggested that reinfection occurs never randomly but preferably to the members of certain household families. From these reinfection analyses, it is inferred that the principal mode of A. lumbricoides transmission in the surveyed rural area is likely to be of 'dooryard type', in which case childen and certain family members are more preferably reinfected. It is also suggested that the preschool childen should be included in the primary targets of mass control programme.

Parasite population biology and host nutrition: dietary fructose and Moniliformis (Acanthocephala)

Experiments were carried out to investigate the possible influence of host-dietary fructose concentration on the relationship between worm burden and the fecundity of Moniliformis dubius. Worm length was found to be dependent both on the fructose concentration of the host's diet and on worm burden. The number of free ovaries/female worm was found to increase linearly with increasing dietary fructose concentration but was independent of worm burden. The length of the ovaries increased with increasing dietary fructose concentration and decreased in response to increases in worm density. The magnitude of the density-dependent reduction in the volume of ovarian tissue/female was decreased in worms from rats fed on diets containing low concentrations of fructose. The numbers of eggs present in the body cavities of the female worms was found to be positively correlated with dietary fructose concentration. At 5 weeks post-infection, mature eggs (containing fully developed acanthor larvae) were found in the body cavities of female worms from rats whose diets contained 3 and 12% fructose, but not in those from rats whose diets contained 1 and 2% fructose (w/w). The experimental results are discussed in the wider context of the influence of host nutrition on parasite population biology.

The prevalence and intensity of Ascaris lumbricoides infections in Moslem children from northern Bangladesh

The results are presented of a horizontal epidemiological survey of intestinal infections of children aged between six months and 15 years in three adjacent villages in northern Bangladesh. On the basis of 203 stool sample examinations, the prevalence of Ascaris lumbricoides, Trichuris trichiura, hookworm and amoebic infections was estimated as 68, 56, 53 and 19%, respectively. Age-specific prevalence data indicated that approximately 90% of the children were harbouring patent Ascaris infections by the time they were four years old and there was some evidence to suggest differences in the pattern of age-prevalence between male and female children. The intensity of Ascaris infection was found to rise to its maximum value within the first four years of life. No significant differences were detected in the mean worm burdens of children aged between four and 15 years. Each child in this age-group harboured on average 10 worms. The frequency distribution of numbers of A. lumbricoides per host was found to be overdispersed, with a value of the negative binomial parameter, k, of 0.44. The degree of aggregation was found to be approximately the same for each age-class of the population between one and 15 years (0.26 less than or equal to k less than or equal to 0.82). No evidence was found to suggest a density-dependent reduction in the weight of either male or female Ascaris within the range one to 43 worms per host.(ABSTRACT TRUNCATED AT 250 WORDS)