intestinal worms
蛔 centers on parasitic worms that live in the intestines, specifically roundworms or ascarids. The meaning is narrow and medical, without broad abstract extensions.
蛔 combines 虫 (insect/worm) with 回, which likely contributes the sound and may suggest the coiled, round shape of intestinal worms.
The insect radical 虫 beside 回 (which looks like a coiled shape) suggests a worm that curls up inside the body: an intestinal worm.
For カイ, imagine a coiled worm crying out 'kai!' as it causes stomach pain: kai -> カイ, and the worm is the source of the cry.