GENETIC-VARIATION IN SYMPATRIC ASCARIS POPULATIONS FROM HUMANS AND PIGS IN CHINA

It has recently been shown using genetic markers that Ascaris in human s and pigs in Central America comprise reproductively isolated populat ions. We present a similar analysis for a region of China in which clo se association between pigs and humans has been the norm for thousands of years, and agricultural practices will result in frequent exposure to eggs from both sources. DNA fragments from selected regions of mit ochondrial and ribosomal DNA. were amplified by PCR and allelic forms identified following digestion with a panel of restriction enzymes, us ing DNA from a total of 115 individual worms from both people and pigs from 2 neighbouring villages. Significant frequency differences in bo th mtDNA haplotypes and the rDNA spacer were found between the 2 host- associated populations, indicating that they represented reproductivel y isolated populations. Mitochondrial haplotype frequencies were diffe rent from those observed in Guatemala and also from other Asian Ascari s populations, suggesting low levels of gene flow between populations. However, we found no evidence for significant heterogeneity in the ge netic composition of Ascaris infrapopulations in either humans or pigs , possibly indicative of agricultural practices in China which have re sulted in a random distribution of alleles within the parasite populat ions.