Research Article

Ascaris infections in humans from North America: molecular evidence for cross-infection

T. J. C. Andersona1*

a1 Department of Biology, University of Rochester, NY 14627, USA


Cases of human Ascaris infection occur sporadically in areas such as N. America and Western Europe, where this parasite is thought to be non-endemic. Clinical case histories suggest that many of these cases may be cross-infections from pigs. I describe patterns of variation in the ribosomal DNA of Ascaris from 9 such cases. For comparative purposes, I also describe patterns of variation in parasites obtained from pigs and humans from worldwide locations. A Hae III restriction site distinguishes two classes of rDNA repeats; repeats bearing this restriction site were found in > 96% of parasites from pig populations worldwide and in all 9 worms from humans in N. America. In contrast, repeats bearing this restriction site were detected in < 2% of parasites from humans in endemic areas. The molecular data clearly incriminate pigs as the source of infection in the N. American cases. I discuss evolutionary and public health implications of incomplete host fidelity in Ascaris.

(Received July 27 1994)

(Revised August 22 1994)

(Accepted August 22 1994)


* Address for reprint Requests: Department of Zoology, university of Oxford, South Parks Road, Oxford Ox1 3ps, UK.