Review of the Common Internal Parasites of Swine

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Review of the Common Internal Parasites of Swine
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Introduction Most parasitic infections of swine
will be diagnosed by finding the adult or larval
parasites or the lesions they produce while
performing a necropsy. However, in reviewing the
common spp. Of swine parasites, a characteristic
egg has also been included. If a more thorough
explanation of the Salient Points, or Feature
of the Life Cycle is necessary, please see your
corresponding lecture notes from the second year
or appropriate texts.
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Unembryonated egg of Ascaris suum (50-75 um x
40-50 um) -eggs are unembryonated in fresh feces,
oval, brownish and possess an irregular
albuminous coat. Occasionally unfertilized eggs
are passed which vary in shape and lack the
irregular coat.
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Embryonated eggs of Ascaris suum When allowed
to stand for a time at room temperature, eggs may
contain larvae.
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Life Cycle features of Ascaris suum The
infective stage (L2) occurs in the eggs which
hatch upon ingestion. Tissue migrations follow
the hepaticotracheal route and may be completed
as early as 10 days. Resulting L4 larvae molt and
mature to egg producing adults in 43-50 days.
Most worms are expelled by 23rd week of patency.
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Adult Ascaris suum heavy infection Large
numbers of adult worms adult may occlude or
perforate the gut. Migration into the bile duct
has been reported. This migration may occur after
treatment.
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Gross liver lesions These are produced by host
response to migrating larvae and maycause
considerable loss at slaughter due to
condemnations. The majority of these may resolve
in a period of 25- 40 days. Some heavy infections
may be found in the intestines without any
visible liver damage.
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Lungs of an 11-week-old pig with chronic
pneumonia and heavy ascarid infection. Thumps
or a soft moist cough which occurs early (7 10
days) after ascarid has been attributed to
migrating larvae. This point has been questioned
by some authors.
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Ascaris suum Salient points Review of the main
features of A. suum infections including Rx-
Piperazine salts, dichlorvos, fenbendazole,
ivermectin, levamisole, and pyrantel. Hygromycin
and pyrantel can be used in feed as prophylatics.
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Oesophagostomum spp. Egg(73 89u x 34
45u) These eggs are typical thin-shelled
strongyle-type eggs and are similar to the eggs
of the red stomach Hyostrongylus.
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Oesophagostomum nodules in large intestine. These
worms are very common in older swine, infection
occurs by ingestion of third stage larvae which
encyst in nodules later to emerge as L4. The
prepatent period is 23 - 53 days according to
species.
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Oesophagostomum salient points The nodular
worm of swine are generally considered
non-pathogenic although very heavy infections may
cause G.I. disturbances.Rxpiperazine salt, TBZ.
levamisole. fenbendazole, ivermectin. Dechlorvos,
and pyrantel.
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Strongyloides ransomi eggs (45-55 u. x 26-35 um)
eggs are similar to other Strongyloides sp. ,
thin-walled and larvated.
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Life cycle features of Strongyloides
ransomi Three routes of infection occur,
prenatal, transcolostral and percutaneous( lung
migration). Prepatent periods are very short ( 2
10 days)
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Section of pig intestine showing location and
small size of adult worms.
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Comparison of litter mate pigs Heavy
infections of Strongyloides, may be fatal or
severly affect growth
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Strongyloides salient points The earliest
parasitic infection producing signs in very young
animals. Rx TBS, levamisole.
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Trichuris suis egg ( 50 60u x 21 25
u) Trichuroid egg with mucoid plugs. These are
common worms of swine
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Trichuris suis adults in pig cecum Like all
whipworms the thin anterior end is embedded in
the mucosa. Heavy infections have been reported
to cause necrosis, edema, hemorrhage, ulcerlike
lesions and nodule formation in the cecum and
colon, but these are generally considered to be
rare.
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Trichuris suis salient points Characteristics
are similar to those of other whipworms, direct
life cycle. Rx dichlorvos, fenbendazole.
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Stomach worms
Three species of stomach worms commonly occur in
swine a. Hyostrongylus rubidus red stomach
worm ( a trichostrongyle) b. Ascarops
strongylina thick stomach worm ( a
spirurid) c. Physocephalus sexalatus thick
stomach worm ( a spirurid
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Hyostrongylus rubidus eggs Diagnosis of this
infection by finding eggs in the feces is
difficult since they are similar to
Oesophagostomum eggs. Cultures can be made and
3rd stage larva identified. Pathology varies
from hyperemia to eroded areas of ulcers. The
occurrence of clinical disease due to these
infections is questionable
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Physocephalus eggs Thick-walled, larvated,
spiruroid type eggs. ( 22 26u x 41 45 u)
Ascarops eggs may be slightly smaller (34 39u x
15 17 u) but are difficult to distinguish from
Physocephalus
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Thick stomach worms in mucosa of
stomach Pathology rare, may cause gastritis with
pseudomembrane formation
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Swine stomach worms salient points Life cycle
are of trichostrongyle and spiruroid types, worms
are common in pastured swine. Rx
Hyostrongylus(TBZ, levamisole, dichlorvos)
spiruroids (dichlorovos).
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Gongylonema egg( 50 70u x 25 37
u) Thick-walled, larvated egg, spiruroid type
egg, larger than stomach worm eggs.
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Gongylonema adult in tongue of pig Non-pathogeni
c, life cycle of spiruroid type, may also occur
in mucosa of the esophagus.
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Metastrongylus spp. Egg( 45 57u x 38
41u) Three species of lungworms commonly occur
in pastured pigs, in the S.E. all produce
thick-walled, larvated eggs similar in size to
Ascaris eggs.
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Metastrongylus adults in pig bronchi A moderate
amount of tissue change( and respiratory
distress) have been directly associated with the
worms. Worms act as vectors of swine influenza
and possibly other viruses.
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Metastrongylus salient points Transmission is
via ingestion of infected earthworms. Rx-
Levamisole, fenbendazole, ivermectin.
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Stephanurus dentatus eggs ( 100u x 60u) Rarely
if ever used in diagnosis, they are found in urine
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Stephanurus dentatus life cycle features Is
direct and a long period of migration occurs,
with a prepatent period of at least 6 months.
Many tissues may be invaded prior to the adults
locating in the renal area.
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Stephanurus adults in urethral cyst
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Stephanurus liver damage The predominant (
necrotic abscesses and fibrosis) produced occur
in the liver during larval migrations. Other
tissues may also be involved.
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Stephanurus salient points The major problem
associated with S. dentatus infections is
condemnation at slaughter. Rx - Fenbendazole,
ivermectin, levamisole(adults only)
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Macrocanthorynchus hirudinaceus eggs (67 110u x
40 65u) Thick-shelled, dark brown,
football-shaped
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M. Hirudinaceus nodules on serosal surface of pig
small intestines. They are due to the proboscis
attachment. Generally non-pathogenic, may
perforate gut
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M. Hirudinaceus adults attached to small
intestines They can be differentiated from
ascarids by presence of proboscis, and wrinkled
sometimes flat appearance
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Balantidium coli cysts Common in swine rarely
pathogenic, 40 60u organism can be recognized
in cyst.
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Balantidium coli on occasion will invade mucosa,
causing ulceration and enteritis of large
intestine. Tetracyclines are effective.
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