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: 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. 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.
parasitology-helminth-nematoda ; Ascaris lumbricoides ; epidemiology ; reinfection

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.
parasitology-helminth-nematoda ; Ascaris lumbricoides ; epidemiology ; reinfection

This study was undertaken to estimate the reinfection incidence of Ascaris lumbricoides after biannual blanket mass chemotherapy and to figure out the characteristic seasonal fluctuation pattern in a Korean rural village. A total of 612 residents from 4 Ri's of Hwasung Gun, Kyunggi Do, Korea was selected and divided into 6 groups according to hamlets, each of which consisted of about 100 inhabitants. Each group received blanket biannual mass chemotherapy with 10 mg/kg of pyrantel pamoate respectively in each month, during the period from April 1977 to September 1978 (Group A-April and October 1977 and April 1978, Group B-May and November 1977 and May l978, and so on). Beforehand Ascaris infection status was evaluated by examining eggs and worms expelled exactly after the first mass chemotherapy checked during the first 6 months and the reinfection incidences were estimated in follow-up examinations during next l2 months by the above two kinds of methods and by detection of young Ascaris positive cases. Young Ascaris was defined as worm shorter than l3 cm and lighter than 500 mg and considered to have introduced to human host during the period from the previous 2 months to 2 weeks. The results were summarized as follows: Beforehand infection rate with Ascaris were 42.3 percent (34.4-50.6 percent by group) by egg detection and 46.2 percent (36.2-51.9 percent by group) by worm detection methods in average. Number of worms per infected case was 2.7 (1.5-4.2 by group) in average. Reinfection rates estimated by egg detection ranged from 8.0 to 3l.5 percent (l6.9 percent in average) in the first follow-up period and from 14.0 to 20.0 percent (l7.5 percent in average) in the second follow-up. Seasonal fluctuation was found marked and there were roughly two peaks, of which the larger appeared from February to March and the smaller from August to September. Reinfection rates by worm detection method ranged from 20.6 to 34.9 percent(25.7 percent in average) and from 14.3 to 21.9 percent (19.6 percent in average) in respective follow-up examinations. Seasonal fluctuation was also observed and the peak incidence appeared one month earlier than those made by egg positive conversion. Number of worms per infected case decreased to 1.6 in average in both follow-up. Young Ascaris detection rates ranged from 6.0 to 12.9 percent (9.4 percent in average) and from 2.3 to 5.8 percent (3.8 percent in average) in respective follow-up. Seasonal fluctuation was also observed. From January to February, the positive rates were up to 12.9 percent and 12.7 percent respectively, which formed the higher peak. Lower one was observed during July to August. From the above results, the actual time of Ascaris reinfection were November to December for the higher peak and May to June for the lower one in Korean population. Pickled vegetable was suggested as a most probable source of Ascaris reinfection during late autumn to winter season.
parasitology-helminth-nematoda ; Ascaris lumbricoides ; reinfection ; epidemiology

The present study was undertaken to determine whether an analysis of the collected worms after chemotherapy with pyrantel pamoate could be used as a method measuring the amount of reinfection of Ascaris lumbricoides in a given population. A total of 398 cases from two villages and one primary school were treated with pyrantel pamoate with dose of 10 mg/kg of body weight. The whole two-day stool specimens after treatment were examined. Out of 279 followed cases, 110 cases (39.4%) were found infected with A. lumbricoides. A total of 527 worms were collected, they were in the range of 1.2 to 32.5 cm in length and 0.0004 to 7.424 gm in weight. The measurements were made on the specimens fixed with 10% formalin. The relationship between the number of worms per positive case(X) and the total weight of worms(Y) showed the positive linear regression; this was expressed by the equation, Y= 2.012X + 1.135 (Sy=4.84, r=0.92). From the above results, it seems that worms of small size may not be considered as a product of crowding effect in heavy infections. The relation between the weight(Y) and length(X) of collected A. lumbricoides was expressed as an equation, Log(e)Y=3.032 log(e)X-8.2903(S.E. of reg. coeff.= 0.040, r=0.957). In the intestinal phase of development, the first increase of the length of the worm, up to 10-12 cm was observed and this followed by the well marked increase of weight from 13 cm upto 32.5 cm in the sexually maturing phase. A total of 285 schoolchildren were treated by pyrantel pamoate, 10 mg/kg of body weight three times each in two months interval. After the second and third treatment, thirteen and fifty-four worms were collected respectively. They were measured in length and weight and were all in the range of 1.2 to 13.2 cm in length and 0.0006 to 0.436 gm in weight except 3 fully matured adults. It is assumed that these young worms, defined as those less than 0.5 gm in weight and less than 13 cm in length should be regarded as those having reinfected during the previous two months period. From this observation, it was possible to calculate the reinfected number of young worms. Therefore, it is suggested that the average number of Ascaris per month per person means the reinfection amount in a certain period of time in an endemic area of A. lumbricoides. In other words, reinfection amount may be expressed by the calculated figure of young worms reinfected in a certain period of time in a population.
parasitology-helminth-nematoda ; Ascaris lumbricoides ; ascariasis ; epidemiology-reinfection ; pyrantel pamoate

Continuous evolution of Omicron variant of 2019-nCoV has resulted in a rapid and simultaneous emergences of novel sub-variants with increased immune escape ability, higher reinfection risk and shorter time interval between infections. Compared with the first infection, the reinfection would still pose exceed risk to people's health although the clinical manifestations of the reinfection might be milder and the risk for severe illness or death is lower. The reinfection is highly associated with people's vaccination status, immunity level, age, working and residential factors. Those who have not received 2019-nCoV vaccination, the elderly and those with comorbidities, especially the previous 2019-nCoV patients with severe/critical illness, are at high risk for the reinfection. Booster doses of vaccine might play an additional role in the prevention of the reinfection and severe illness on the basis of natural immunity.
Aged ; Humans ; COVID-19 ; Reinfection/epidemiology* ; SARS-CoV-2 ; Immunity, Innate