Biology Reference
In-Depth Information
female parasites starts. A study by Mejer and Roepstorff
15
showed that
pigs that are naturally exposed to a paddock contaminated with
A. suum
show the highest egg excretion 17 weeks after being introduced onto the
paddock. After this point, egg counts begin to drop. The lifespan of adult
A. suum
worms can be over 1 year. This is significantly longer than the
average life of a fattening pig these days. Therefore, once adult worms are
present in pigs, the egg shedding increases with the age of the pigs unless
the worms are cleared from the intestine by anthelmintic therapy.
Ascariasis is present in most countries worldwide. However, few
countries have up-to-date information on its prevalence. Many of the
prevalence studies were performed decades ago, making the results
unrepresentative for the current situation.
Table 16.1
provides an over-
view of the studies in the literature investigating the prevalence of
A. suum
. Different studies applied different methods to determine the
presence of
Ascaris
in pigs. Some used the percentage of rejected livers as
a measure of parasite exposure; others checked the presence of worms by
examining the intestinal tract at slaughter or by coprological examination
of fecal samples to detect parasite eggs. The table shows the results of
studies that were performed in different countries, in different times and
settings. Because of this, it is not possible to draw conclusions concerning
epidemiological trends of ascariasis on pig farms. However, two
comparable studies from Denmark performed in 1989 and 2010, two
decades apart, show that the situation has remained roughly the same
with
A. suum
being present on 88% and 76% of the investigated farms,
respectively.
There are several reasons why
Ascaris
is still so prevalent in current
high intensity pig farms. First, because the ascarid has a direct life-cycle
and is therefore not reliant on other organisms for its transmission to new
hosts. Second, the female parasitic worms are highly fecund and are
capable of producing hundreds of thousands of eggs per day that
contaminate the surroundings instantaneously. Third, the eggs are
extremely resistant to external environmental factors, ensuring their
survival for up to several years in the appropriate conditions. Finally, and
maybe most importantly, the lack of efficient diagnostic tools to shed light
on the problem at a farm level, together with the seemingly unimportant
health consequences of
A. suum
infections, have led to a certain negligent
attitude towards roundworm infection on the part of the farmer. Yet,
today, the economic pressure on the pig industry is of such extent that
production efficiency is crucial and nobody can afford to neglect the
treatment of a parasitic ailment like ascariasis, which has shown to
significantly affect economic profitability.
16
e
20
However, in order to
effectively control
A. suum
infections on a pig farm, it is necessary for the
farmer to be informed of the evolution of the “
Ascaris
-status.” In order to
do so, good diagnostic tools are indispensable. These tools will allow for
