Abstract:
BACKGROUND: Hookworms are blood-feeding nematodes that parasitize the small intestines of many
mammals, including humans and cattle. These nematodes are of major socioeconomic importance and
cause disease, mainly as a consequence of anaemia (particularly in children or young animals), resulting in
impaired development and sometimes deaths. Studying genetic variability within and among hookworm
populations is central to addressing epidemiological and ecological questions, thus assisting in the control
of hookworm disease. Mitochondrial (mt) genes are known to provide useful population markers for
hookworms, but mt genome sequence data are scant.
RESULTS: The present study characterizes the complete mt genomes of two species of hookworm,
Ancylostoma caninum (from dogs) and Bunostomum phlebotomum (from cattle), each sequenced (by 454
technology or primer-walking), following long-PCR amplification from genomic DNA (~20–40 ng) isolated
from individual adult worms. These mt genomes were 13717 bp and 13790 bp in size, respectively, and
each contained 12 protein coding, 22 transfer RNA and 2 ribosomal RNA genes, typical for other
secernentean nematodes. In addition, phylogenetic analysis (by Bayesian inference and maximum
likelihood) of concatenated mt protein sequence data sets for 12 nematodes (including Ancylostoma
caninum and Bunostomum phlebotomum), representing the Ascaridida, Spirurida and Strongylida, was
conducted. The analysis yielded maximum statistical support for the formation of monophyletic clades for
each recognized nematode order assessed, except for the Rhabditida.
CONCLUSION: The mt genomes characterized herein represent a rich source of population genetic markers
for epidemiological and ecological studies. The strong statistical support for the construction of
phylogenetic clades and consistency between the two different tree-building methods employed indicate
the value of using whole mt genome data sets for systematic studies of nematodes. The grouping of the
Spirurida and Ascaridida to the exclusion of the Strongylida was not supported in the present analysis, a
finding which conflicts with the current evolutionary hypothesis for the Nematoda based on nuclear
ribosomal gene data.
