Ascaris infections in humans from North America: molecular evidence for cross-infection.
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.
Anderson
T J
TJ
Department of Biology, University of Rochester, NY 14627.
D000328:Adult; D000818:Animals; D001196:Ascariasis / Q000635:transmission*; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D018509:DNA, Helminth / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008969:Molecular Sequence Data; D009656:North America / Q000453:epidemiology; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic / Q000235:genetics*; D013552:Swine / Q000469:parasitology*
D018509:DNA, Helminth; D004275:DNA, Ribosomal