Author:
ANDERSON T. J. C.,JAENIKE J.
Abstract
We describe a variety of restriction site polymorphisms in the
introns
of Ascaris nuclear genes and in the ribosomal DNA
spacers. We use these markers, in addition to previously described
mitochondrial variation, to clarify our understanding
of the epidemiology of Ascaris in Guatemalan villages where
humans and pigs occur in sympatry and to describe the
genetic structure of host-associated Ascaris populations from
world-wide locations. Intron sequences were amplified from
individual worms and alleles defined by endonuclease digestion. Two loci
were monomorphic, while 4 length variants and
22 point mutations were detected in the other 7 loci. Within sympatric
Guatemalan populations no single locus from either
the nuclear or mitochondrial genome was fixed for alternative alleles,
although allele frequencies were significantly different
at many loci. Phenograms constructed from multilocus nuclear genotypes
of
individual worms failed to reveal a single case
of cross-infection, and demonstrate that divergent mtDNA genotypes are
segregating within host-associated populations.
On a world-wide scale, the data suggest that extant worm populations result
from a single host shift, although characterization of genetic variation
in additional loci will be necessary to confirm this. The direction and
the
geographical origin
of the host shift were unresolved. Overall 65% of nuclear genetic variation
was found within populations, host (human
or pig) explained 18%, while geographical variation within
host-associated populations explained 17%. The results (a)
demonstrate the utility of introns for studying the epidemiology of
parasites showing limited allozyme variation (b) suggest
that programmes aiming to control Ascaris infection in the
human population can safely ignore zoonotic infection from
pigs and (c) illustrate the problems inherent in using single genetic
markers to make inferences about the epidemiology
of closely related parasite taxa.
Publisher
Cambridge University Press (CUP)
Subject
Infectious Diseases,Animal Science and Zoology,Parasitology
Cited by
99 articles.
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