The "crowding effect" phenomenon in Ascaris lumbricoides.

Ascaris lumbricoides worm populations were studied from 150 Filipino children (0-14 years) dewormed with pyrantel pamoate (Combantrin) or oxantel-pyrantel pamoate (Quantrel). Populations were classified according to intensity of infection: very light, light, moderate or heavy. A total of 2072 adult worms were sexed (939 males and 1133 females) and weighed. Descriptive statistics on the weights obtained from each sex were derived and one-way ANOVA was performed to compare the mean weights among the 4 intensity classes. Linear regression analysis (individual worm weight versus total worm burden) was also employed to equalize the possible influence of host factors. Statistical analysis revealed that mean weights of both sexes were significantly different and decreased as worm burden increased. This strongly suggests that the "crowding effect" phenomenon may also apply to Ascaris lumbricoides, and not only to tapeworms, as reported in the literature.