In vivo and in vitro studies on the sonographical detection of Ascaris lumbricoides.

Intestinal ultrasound, a frequently applied diagnostic tool in industrialized nations, has recently also been introduced in tropical regions. This study attempts to describe the anatomical and sonographical features of Ascaris lumbricoides in the human intestine. In the course of a schistosomiasis morbidity study in Madagascar, 581 inhabitants of a rice-farming village on the high plateau of the island had their stools examined by means of a modified Kato-Katz thick smear technique (four slides per sample); 53% had eggs of Ascaris lumbricoides in their stools. Twenty-two individuals underwent intestinal ultrasound examination and, in six cases, Ascaris lumbricoides was visualized. All six patients showed eggs upon stool examination. At ultrasound, the parasite was seen as a large, curved echogenic strip (4-6 mm in diameter) with an inner, anechoic, longitudinal canal. The image resembled a winding highway, the central structure representing the pseudocoel of the parasite. Patients were treated with mebendazole. The excreted worms of one patient were scanned under water, showing the same characteristics as in vivo. We conclude that Ascaris lumbricoides has a characteristic sonographical appearance and should not be a confounding factor in studies using intestinal ultrasound.