It has recently been shown using genetic markers that Ascaris
in humans and pigs in Central America comprise
reproductively isolated populations. We present a similar analysis for
region of China in which close 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 mitochondrial
and ribosomal DNA were amplified by
PCR and allelic forms identified following digestion with a panel of
restriction enzymes, using DNA from a total of 115
individual worms from both people and pigs from 2 neighbouring villages.
Significant frequency differences in both
mtDNA haplotypes and the rDNA spacer were found between the 2 host-associated
populations, indicating that they
represented reproductively isolated populations. Mitochondrial haplotype
frequencies were different from those observed
in Guatemala and also from other Asian Ascaris populations,
suggesting low levels of gene flow between populations.
However, we found no evidence for significant heterogeneity in the
genetic composition of Ascaris infrapopulations in
either humans or pigs, possibly indicative of agricultural practices
in China which have resulted in a random distribution
of alleles within the parasite populations.