Observations on the Epidemiology of Ascariasis in a Region of High Hookworm Endemicity

Abstract

The incidence of ascariasis is singularly low in the sandy coastal plain of s.-e. U.S. where hookworm disease is highly endemic. Ascaris-infected families were found to be typical of the hookworm-infected families of the same region. Viable ascaris eggs, usually some with larvae, were found in dooryards of all families examined but in the dry season they were scarce and limited to the entranceways where dampness was maintained by househoud refuse. Ascaris infections in pigs were light and infrequent as compared with reported findings in other areas. In experimentally inoculated plots, development and survival of human ascaris eggs were enhanced by the presence of clay in the soil. Splashing of raindrops transported eggs at least 1.5 m. laterally and onto vertical surfaces up to 30 cm. above ground. The sorting action of rain concentrated the eggs in the topmost stratum of sandy soil but in soil containing clay they were buried under a thin buffering layer of fine colloidal particles. Evidence indicates that the low endemicity of ascariasis in the hookworm belt is due chiefly to the sandy character of the topsoil which, in contrast to denser soils, does not contain sufficient light colloidal elements to retain surface moisture and to stratify the eggs just below the ground surface where they are protected and at the same time are advantageously situated for transfer to new hosts.