Biology Reference
In-Depth Information
natural exposure to
A. suum
.
71,72
Pathology and clinical signs have been
correlated with inoculation dose in surviving calves, but the link to
mortality is less clear. Some animals have thus died after receiving “low
doses” of 10,000
100,000 eggs whereas others have survived multiple
doses adding up to 11 million eggs.
80,81
A. suum
has also been shown to cause varying levels of gross liver
pathology in cattle. In one study, no milk spots or larvae were detected
after inoculation of four 2
e
3-day-old calves with a single dose of 10,000
A. suum
eggs
80
whereas milk spots were noted 3
e
5 days p.i. and larvae
were isolated from the liver of 4-week-old calves infected with 2 million
eggs.
78
Larval migration may have been underestimated due to subop-
timal recovery methods. Alternatively, the difference in results may
reflect the variation in age and/or dose level as it is likely that overall
migration success is considerably lower in an inappropriate host. At
slaughter, livers from cattle given 2000 or 5000
A. suum
eggs were all
condemned.
80
Mature
A. suum
has been observed in the intestine or bile ducts of
lambs at several abattoirs.
82
e
84
These infections were probably the result
of exposure to pastures contaminated with pig feces
85
as worms from
lambs have been genetically characterized to be of pig origin (Nejsum,
unpublished data). Worms in the bile ducts have been shown to cause
pathological changes
83
but clinical manifestations due to intestinal worms
are to our knowledge unknown. As for cattle, transient lung symptoms
days 5
e
14 p.i. have been reported for lambs and kids after experimental
exposure to
A. suum
.
86,87
Symptoms included dry coughs, dyspnea and
pneumonia, and an animal died. Larvae were isolated from the lungs in
both studies.
Condemnation of 70% of the lamb livers from one farm was associated
with
A. suum
,
88
and the pathological changes were similar to those
described in an earlier
A. suum
suspected case in lambs.
83
Yellow
e
white
plaques (15 mm in diameter) were observed on the liver from a lamb that
also harbored
Ascaris
spp. in the bile ducts.
84
Histological examination of
lamb livers after supposedly
Ascari
s spp. infection showed intensive
eosinophil infiltration of the portal tracts, parasite tracks in the paren-
chyma and portal fibrosis.
83
However, other researchers have reported an
apparent lack of macroscopic milk spots in lambs experimentally infected
with
A. suum
.
87,89
The lack of interlobular connective tissue in lambs is
considered the main reason why “white spots” do not develop in this host
animal.
87
They are therefore critical to the reports suggesting that
condemnation of liver at abattoirs should be related to white spots
caused by
A. suum
but do not refute that pathological changes take place
in the liver.
The importance of
A. suum
in other livestock species is not known. Pigs
fed livers and lungs from
A. suum
inoculated chickens (clinically
e
