Biology Reference
In-Depth Information
Lack of convincing and consistent findings on weight gain benefits in
treatment trials in commercial herds create problems in motivating
farmers and advisors, including decision making on when to intervene
and how. From a farmer's perspective, the apparent paradox that better
control and reduced transmission may in some cases lead to more livers
condemned at slaughter due to later exposure and lower levels of
immunity makes it even harder to understand. A later acquisition of
A. suum
(and
Oesophagostomum
spp.) by growing pigs in intensive
systems may, however, still have a beneficial impact on the economics of
production as numbers of both migrating larvae and adults may be
negligible while the duration of the infections may be short. Therefore
the overall impact of a relevant intervention may still be substantial.
A. suum
can cause significant clinical manifestations and reduce carcass
quality in cattle and sheep. However, in areas of industrialized farming
systems we expect the clinical impact of
A. suum
to be limited since most
farms are specialized for a single type of livestock, and pig slurry is
seldom applied on ruminant grazing areas. In contrast, in more extensive
livestock production systems with mixed species or in areas where live-
stock are roaming freely, as is the case in many developing countries, the
impact of
A. suum
might be higher although not yet documented.
Lastly, the more subtle impact of
A. suum
on the course and impact of
other infections, including the possible interference with vaccinations,
should not be neglected. There is circumstantial evidence that
A. suum
together with other helminths result in more pronounced effects, bacterial
and viral co-infections are potentiated, and Th1-dependent vaccinations
may fail to protect as stipulated. There is an urgent need to assess the
impact of
A. suum
in this context. This may well turn out to be just as
important as any direct effect.
References
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