Biology Reference
In-Depth Information
There are also indications that slaughter yield and meatiness
(percentage lean meat according to the EUROP scale) can be affected as
they were decreased by 2.7 and 6.1%, respectively, by helminth infections
(
A. suum
and
Oesophagostomum
spp.) when pigs are fattened in pens with
slatted floors (
n
60).
62
Corresponding figures for pigs on shallow litter
¼
(5
20 cm of straw and fecal matter, removed frequently) were 1.7 and
4.2%. Infection status of animals was apparently determined by fecal egg
counts twice during the fattening period but it was not clear when
randomization took place. This study confirmed an earlier study in
fatteners naturally infected with
A. suum
(post-mortem examination)
showing significantly poorer carcass characteristics (4% reduction in
relative ham size and increased fat-to-meat ratio) as compared to unin-
fected pigs.
17
However, the same study failed to show an effect on weight
gains. Matthes et al.
63
reported increased weight gains, carcass weights
and feed intake after treatment with ivermectin at entry to the fattening
unit as compared to untreated controls (
N
e
¼
3521 pigs). However, the
farm had a history of both
A. suum
and sarcoptic mange and it was not
possible to separate the effects.
INDIRECT EFFECTS
Indirect effects of
A. suum
infections are related to co-transmission of
other pathogens with the parasite eggs, enhanced pathogenicity associated
with the migratory phase or the intestinal phase, and what can be termed
as a “systemic immunomodulatory effect.” With a few exceptions, these
studies are based on few animals and are seldom repeated by other inves-
tigators. Nevertheless, infective eggs may potentially contain pathogenic
E. coli
64
but whether they can in fact transmit other infectious diseases, as
shown for the bird helminth
Heterakis gallinarum
and
Histomonas
meleagridis
,
65
remains to be explored. Lung phase studies have focused on
whether larvae with a contaminated cuticle may lead to lung infections, of
which there is little evidence
66
or whether the associated lung pathology
makes the infected pig more vulnerable to air-borne infections. Underdahl
and Kelley
67
first reported a marked exacerbation of viral lung lesions by
migrating ascarid larvae in experimentally infected pigs. A reduced lung
clearance of bacteriawas later found in a study reporting a sevenfold higher
bacterial load in lungs of
A. suum
-infected pigs as compared to controls 2
hours after aerosol exposure to
E. coli
.
30
In addition, a higher pathogenic
effect of an aerosol with
Pasteurella multocida
has been reported during the
lungmigration phase in
A. suum
-infected mice.
68
The migratory lung phase
may perhaps in itself lead to lung lesions characterized by small spots of
fibroplasia with surrounding hemorrhage as indicated by a higher occur-
rence of liver milk spots in pig with these lung lesions.
69
