Biology Reference
In-Depth Information
mortalities
1,2
(see Chapter 14). Despite the impact of ascariasis and the
increased attention in recent years through the Millennium Development
Goals
3
and the Neglected Diseases Initiative,
4
treatment is confined to
a handful of drugs, and the prevalence of the disease remains high in
many areas of the world.
5
Ascaris
is transmitted directly by the fecal
oral route. The human and
porcine hosts become infected by ingesting larvated
Ascaris
eggs from the
environment (e.g. in contaminated water or food); third-stage larvae
hatch from the eggs migrate through the intestinal wall into the blood-
stream, and then through the liver and to the lungs (
e
hepatopulmonary
migration), after which the larvae ascend the trachea, are swallowed and
then develop as dieocious adults in the small intestine. The damage
caused by the migrating larvae can be significant, in addition to the effects
of the large worms (10
ΒΌ
20 cm long) in the small intestine, relating to
occlusion of the lumen, perforation of the intestinal wall or occlusion of
bile/pancreatic ducts and death in hosts with high burdens.
6
Morpho-
logically,
Ascaris
of humans (
Ascaris lumbricoides
) and pigs (
Ascaris suum
)
are indistinguishable, and their status as separate species remains
controversial,
7
with reported cases of
A. suum
infections in humans
8
(see Chapters 8 and 11). Given the close genetic relationships between
A. lumbricoides
and
A. suum
9
as well as between the human and
porcine hosts, the
Ascaris
-swine model
10
provides an excellent system to
explore many aspects of
Ascaris
and ascariasis at the molecular level
(see Chapters 14 and 16).
The development of high-throughput nucleic acid sequencing and
bioinformatic technologies are having far-reaching implications for all
areas of the biological sciences, including the study of geohelminths of
major socioeconomic importance. These technologies provide the pros-
pect of exploring these helminths on a scale that, even in the last few
years, was unachievable for all but the largest of sequencing centers,
providing unprecedented opportunities to investigate key aspects of the
biology of these critically important parasites. Such advances also provide
a window to revitalizing the urgently needed development of new
interventions through the identification and characterization of novel
drug and vaccine targets as well as the prospects of defining genetic and
biological markers for improved diagnostic applications. To facilitate such
efforts, we recently sequenced the 273 Mb draft genome of
A. suum
utilizing massively parallel sequencing and advanced bioinformatics and
also undertook extensive comparative analyses.
11
In this chapter, we
(1) describe the advanced methodologies used to sequence, assemble, and
annotate the
A. suum
genome, (2) review the salient features of this
genome and associated transcriptomes, and (3) emphasize the unique
prospects that knowledge of this genome provides for investigations into
the genetics, evolution, immunobiology, epidemiology, ecology of
Ascaris
e
