Biology Reference
In-Depth Information
the applied control strategies, the use of correct diagnostic tools is crucial.
Different possibilities are at hand to diagnose the presence of
A. suum
infections on pig farms.
Presence of Worms
Most farmers determine infection by observing expelled adult worms
after anthelmintic treatment.
21
Although the expelled worms might not
have conserved their exact shape and color, a farmer should be able to
detect these spaghetti-like organisms mixed with the feces. When
immature worms, which are notably smaller, are expelled, identification
by the untrained eye might be harder. Clinical signs such as unthriftiness,
difficulties breathing and wheezing, and indirect signs like decreased
growth rate and overall lower food conversion efficiency could also
indicate
A. suum
infection but are hardly ever associated with ascariasis
by the farmer because of their non-specificity.
The presence of adult worms in the small intestine of pigs can be
registered at slaughter. However, except in experimental settings, the
detection of worms in the intestine is hardly ever done in practice. If
performed, one must keep in mind the time between last anthelmintic
treatment and slaughter, as the larval stages in the intestine are small and
easily overlooked. This could lead to wrong conclusions when no worms
could be detected. The detection of adult parasites is, however, only
a qualitative measure, and not a quantitative one, as the number of adult
worms is not representative of the amount of migrating larvae the pig has
been exposed to. Regardless of the dose regimen, the number of worms
that end up in the small intestine is generally inconsistent and inde-
pendent of the intake of infective stages.
23
Furthermore, there seems to
exist an inverse relationship between the number of adults found in the
intestine and the amount of eggs given during a single experimental
infection dose.
11,24
Additionally,
Ascaris
populations are strongly aggre-
gated within the pig population with few pigs carrying the majority of
the worms while most of the pigs carry few or even no adult
worms at all.
11,25,26
The reason for this is currently still unknown (see
Chapters 7 and 12). It seems that host genetics could be an important
factor.
27
Fecal Examination
Detecting the eggs excreted by adult female worms can prove the
presence of adult worms in the intestine. For this, coprological tech-
niques of sedimentation/flotation or McMaster can be applied.
28
Both
techniques make use of the buoyancy of parasite eggs in a dense
salt/sucrose solution to separate the eggs from the fecal debris. The
