Biology Reference
In-Depth Information
unaffected) became infected and it is possible that
A. suum
may cause
illness in humans if raw chicken livers are consumed.
90
D
ISCUSSION AND CONCLUSION
S
Losses due to ascariasis in pigs can be summarized as (1) farm economic
losses due to clinical effects (although limited), reduced growth and feed
conversion efficiency and costs of control (e.g. use of anthelmintics), (2)
abattoir operator losses due to condemnation or downgrading of livers
and lower product quality, and (3) potential interference with vaccinations
and higher risk of co-infections. Apart from the cost of liver condemna-
tions that can be extrapolated from available data, it is difficult to get an
overall impression of relative importance and to assign values to these
losses. An attempt to address some of the problems associated with
economic evaluation of worm control has been reported,
91
indicating gross
margin increases of 3
per average present finisher per year after
strategic de-worming during the fattening period. In the USA, the poorer
feed conversion has been estimated to account for a total loss of US$60.1
million in 1999, based on a 5.6% higher feed intake to reach target weight
in about 50% of the pigs slaughtered.
92
This loss was considerably larger
than costs due to liver condemnations. Gross margin increases with 3 to
12
e
12
V
per average present finisher per year, depending on the cyclic pig
price conditions.
After reviewing the existing literature, it is most likely that pigs heavily
exposed to
A. suum
will experience a reduction in feed utilization and
perhaps also weight gain. The effect may be transient and perhaps more
strongly associated with the intestinal phase than the early stages of infec-
tion. Further, it is striking how difficult it has been in more recent studies to
demonstrate significant reduced productivity due to
A. suum
V
both in
experiments and on-farm.
42
As mentioned earlier, this may be related to the
strong overdispersion of the
A. suum
infection
e
only a limited number of
animals are infectedwithhigh numbers ofworms at any one time
e
together
with well-balanced diets rich in essential amino acids in most intensive
systems. This can explain the oftendramatic effects reportedseveral decades
ago and the pronouncedeffects of anthelmintic treatments inmore extensive
systems, e.g. indeveloping countries.
A. suum
andother intestinal helminths
most likely constitute a serious problem of disease and productivity in poor
farming communities worldwide. The impact of
A. suum
in these systems
needs to be addressed in future studies. Another obvious explanation is, of
course, that there is no measurable impact due to a high degree of co-
adaptation between parasite and host. However, any researcher having
necropsied
A. suum
-infected animals will find it hard to believe that the
marked pathological changes do not impact upon function.
e
