The dispersion of Echinococcus granulosus in the intestine of dogs.

We studied the dispersion of adult Echinococcus granulosus in the intestine of experimentally infected dogs at 2 scales of habitat use. On a coarse scale, worms were found most frequently in the anterior third of the small intestine. On a fine scale, clumps or aggregations, typically of 4-5 worms in an area of 12 mm2, occurred throughout the anterior two-thirds of the intestine. The most likely proximate cause of aggregative behavior is attraction between individual worms. There are at least 2 equally plausible ultimate causes of the behavior: to enhance cross-fertilization and to improve the quality of the environment. Restriction of worms to the anterior small intestine may be a consequence of aggregative behavior on a finer scale or a response to different proximate and ultimate factors.