Biology Reference
In-Depth Information
Other management practices like the use of the all-in-all-out
system and early weaning are linked to lower prevalence of
A. suum
.
3,48,68,82
In the all-in-all-out production system, pigs are moved
into and out of facilities in distinct groups with the hope that, by pre-
venting the commingling of groups, the spread of disease is reduced. This
practice also allows for a period of thorough cleaning and disinfecting
between subsequent groups of animals. Early weaning of piglets (3
e
5
weeks) also seems to be associated with a reduced risk of
A. suum
infection.
68
However, it is likely that this can be attributed to the fact that
both these parameters are associated with other factors that are more
important for parasite survival, like, for instance, the use of more tradi-
tional rearing methods or poorer general pen hygiene.
Reducing contact of pigs with their own fecal deposits or from pigs
from previous rounds is important. Consequentially, housing of pigs on
slatted floors seems to reduce the chance of parasite infestation compared
to solid or partially slatted floors.
48,82,83
Increased risk is associated with
bedding being present in the pens. The use of bedding material may
provide extra refugia that promote egg embryonation and hamper the
effectiveness of repeated cleaning and disinfection measures. Evidently,
the stocking density in the pig house will also be important,
82
as chances
of pens containing pigs with patent infections will increase.
Positioning the water supply in the dung area instead of in the lying
area or the feeding troughs seems to be associated with a decreased
prevalence of
A. suum
.
68
Water spillage in areas where eggs are present
will enhance the chances for survival of the eggs due to constant
humidity. Despite the extremely rigid eggshell, eggs do not embryonate
when relative humidity is low, for instance in the dry resting areas in pig
pens, or when floor temperatures are lower than 15
C. Additionally, pig
urine also seems to exhibit a strong inhibitory effect on the development
of
A. suum
eggs.
40
Once in the environment, the eggs will embryonate
until the infective larvae are present inside the egg. Only then is the egg
infective for a new host. In a Danish study it was shown that
A. suum
eggs
could embryonate on a pasture within 4
e
6 weeks during a normal Danish
summer.
14
These results were supported by experiments in laboratory
conditions, during which it was observed that although motile larvae
were noticed from 4 weeks post-incubation, an incubation period of at
least 6 weeks at room temperature was needed for eggs to become
infective in mice.
84
When environmental factors like temperature, oxygen
availability, and relative humidity are suboptimal, the time for larvae to
become infective increases.
40
This is reflected by the fact that white spot
levels seem to vary within farms depending on the season. Presumably,
the rising temperatures in spring and summer allow simultaneous
development of infectious stage larvae in the eggs that have spent the
winter in the pig pens. This would increase the amount of infective eggs
