Download Large Animal Internal Parasites

Large Animal Internal Parasites
Routine fecal examination of horses will reveal parasitism by four types of
parasites. Strongyloides westeri, Parascaris equorwn, Strongyles (large and
small, sp. are not distinguishable by eggs), and Anoplocephala sp. (eggs of the
two important sp. in the U.S. are indistinguishable). However, other sp. of
parasites occur and will be reviewed. If a more thorough explanation of the
“Salient Points” or “Features of the Life Cycle” are necessary please refer to your
corresponding lecture notes from the second year or an appropriate text.
Strongyloides westeri eggs (40-52 u x 32-40 u)
Thin walled, larvated egg, typical of Strongyloides
Strongyloides sp. Life Cycle:
Parthenogenic parasitic females are found in the small intestine of foals,
animals become immune and the adults are not generally found in the
intestine after six months of age, infection occurs, via milk, skin
penetration and ingestion, these parasites have a short prepatent period
(5-6 days) and may be found in very young horses.
Parascaris eguorum eggs (90-100u)
thick-shelled ,globular shape, eggs are not larvated in fresh feces, some
eggs here contain the infective larvae.
Parascaris equorum emerging from a perforated portion of the small
intestine, this may occur in heavy infections. Pathology due to
migrating ascarid larvae is considered to occur .
Gastrophilus
Almost all horses are infected with bots Gastrophilus intestinalis sometimes with
G. nasalis and rarely in the U.S., G. hemorrhoidalis. Bots cannot be diagnosed by
fecal examination. Finding eggs on the horse's hair is an indication of internal
infection. Unless treated most horses are infected.
Cutaneous habronemiasis:
“Summer Sore” on the prepuce of horse, develop from larvae being
deposited or escaping from vector flies feeding around a wound or abrasion.
May also cause pulmonary granulomas if larvae invade the lungs. In the
stomach Habronema sp. produce mucus exudate, and D.megastoma produce
tumor- like lesions along the margoplecates
Oxyuris equi egg(42-90 u)
Eggs are elongated and slightly flattened, with a operculum like plug at one end,
these are rarely seen in feces.
Oxyuris equi adult females:
More commonly found in foals, females rupture during their migrations to the
rectum and anus, eggs are released and attach to walls, fixtures, etc. ,
development to infective larvae within the eggs is fast, (3-5 days), prepatent period
-5 months
Loss of Hair:
Due to pruritus caused by migrating female 0. equi, this irritation and resulting hair
loss is the principle problem associated with the infection, and the common means
of diagnosis
Anoplocephala sp. Eggs -(50-60 u)
Eggs possess pyriform apparatus, spp. identification is not possible on egg
morphology .
A. magna in horse intestine:
Largest (up to 12 in) of two common spp. in the U.S.
found in posterior portion of small intestines may produce
catarrhal or hemorrhagic enteritis
Anoplocephala perfoliata adults:
Smaller than A. magna (1-2 in.) occur in larger numbers more , pathogenic of the
two spp. , produces ulcers, and may induce occlusion of ileo-cecal valve, or
intussusception in this area.
. Strongyle egg -{70-85 u x 40-47 u)
Spp. cannot be identified by egg morphology , egg here can be compared to Parascaris
equorwn and Strongyloides westeri.
The large strongyles are pathogenic because of their larval migrations, adults
attach to the mucosa of the large intestine and cecum and suck blood. Some
Triodontophorus spp. produce mucosal ulcers
Strongylus vulgaris caused aneurism in mesenteric artery due to
larval migrations
Strongylus vulgaris related intestinal infarction
Due to emboli produced by S. vulgaris larval migrations in mesenteric, arteries.
Other large strongyle larvae (S. edentatus & S. equinus) produce lesions during their
migrations in liver, diaphram and other viscera.
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Comparison of large and small strongyles
Symptoms of Parasitic Infestation in
Cattle
• Parasites to the
stomach and
intestines cause:
• Anemia
• Scouring
• Depression
• Death
Description of Parasitic Infestation
• Roundworms:
• Found in the digestive
system
• Most important
parasites from an
economic standpoint
• Mostly in stomach and
intestines
Stomach Worm
• Several species of stomach worm
• Twisted stomach worms and brown stomach
worms are the most important.
• Found in all classes of livestock
• Most common in cattle, sheep and horses.
• Penetrates the stomach lining
• Causes severe damage
Calf Scours
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Diarrhea
Two main forms
Hypersecretion
Malabsorption
Result of Diarrhea
Dehydration
Dryed out mouth
Strongyles
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Several species
Attack all species
Greater affect on young
Blood sucking parasites that attach to the
lining of the intestines
Ascarids
• Parasites of cattle, sheep, horses and hogs
• Affects young mostly
• The larvae burrow into the wall of the
intestines and migrate through the liver, heart,
and finally the lungs
Internal Parasites of Goats and Sheep
Strongyloides
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Strongyloides stercoralis is an unusual "parasite" in
that it has both free-living and parasitic life
cycles. In the parasitic life cycle, female worms are
found in the superficial tissues of the human small
intestine; there are apparently no parasitic
males. The female worms produce larvae
parthenogenically (without fertilization), and the
larvae are passed in the host's feces. The presence
of nematode larvae in a fecal sample is
characteristic of strongylodiasis. Once passed in
the feces, some of the larvae develop into "freeliving" larvae, while others develop into "parasitic"
larvae. The "free-living" larvae will complete their
development in the soil and mature into free-living
males and females. The free-living males and
females mate, produce more larvae, and (as above)
some of these larvae will develop into "free-living"
larvae, while other will develop into "parasitic
larvae."
Tapeworms
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Broad tapeworm - Moniezia expansa
Fringed tapeworm - Thysanosoma actinioides
Hydatid cysts - Echinococcus granulosus
Cysticercosis - Taenia ovis
Taenia hydatigena
Gid - Taenia multiceps
Broad tapeworm
- Moniezia expansa
The life cycle of Moniezia expansa involves sheep as the definitive host and soil mites as the
intermediate host. The tapeworm's eggs are passed in the sheep's feces, and mites are infected
when they eat the eggs; the metacestode stage in the mite is called a cysticercoid. Sheep are
infected when then ingest infected mites. This species of tapeworm is unusual in that each
proglottid contains two sets of female reproductive organs
Fringed tapeworm - Thysanosoma actinioides
• Definitive hosts: ruminants
• Site of infection: small intestine
Typical size: up to 30 cm long
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Distribution: cosmopolitan
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Intermediate hosts: cysticercoids
develop in psocid lice; these lice are
ingested along with vegetation
Hydatid cysts - Echinococcus granulosus
• The life cycle of Echinococcus granulosus includes dogs (and other
canines) as the definitive host, and a variety of species of warm
blooded vertebrates (sheep, cattle, goats, and humans) as the
intermediate host. The adult worms are very small, usually consisting
of only three proglottids (total length = 3-6 mm), and they live in the
dog's small intestine. Eggs are liberated in the host's feces, and when
these eggs are ingested by the intermediate host they hatch in the
host's small intestine. The larvae in the eggs penetrate the gut wall
and enter the circulatory system. The larvae can be distributed
throughout the intermediate host's body (although most end up in
the liver) and grow into a stage called a hydatid cyst.
Taenia hydatigena
• The life cycle of the Taenia tapeworm
starts in the host’s intestine, the host
being a dog or cat. The worm can be
unbelievably long (up to 5 yards for
Taenia hydatigena) and is made of
segments. Each segment contains an
independent set of organs with new
segments being created at the neck and
older segments dropping off the tail. As
segments mature, the reproductive tract
of the segment becomes more and more
prominent until it consists of a bag of
tapeworm eggs. These segments, called
proglottids, are passed with the feces
into the world where an unsuspecting
intermediate host (mouse, rabbit, deer,
goat etc.) swallows one while feeding.
Gid - Taenia multiceps
• The life cycle of this parasite involves warm blood vertebrates as both
the intermediate and definitive hosts.
• Infections with cenuri can cause pathology in the intermediate
host. Human infections (acquired by accidental ingestion of eggs)
have been reported. The cenuri of T. multiceps (sometimes called
Cenurus cerebralis) can infect the brains of sheep/goats, causing a
disease referred to as "gid" or "staggers." These terms refer to the
behavior of sheep/goats infected with this parasite.
Flukes - Trematodes
• Common liver fluke - Fasciola hepatica
Flukes - Trematodes
• The common name of this parasite, the "sheep liver fluke," is somewhat
misleading since this parasite is found in animals other than sheep (including
cattle and humans), and the parasite resides in the bile ducts inside the liver
rather than the liver itself. This species is a common parasite of sheep and
cattle and, therefore, relatively easy to obtain. Thus, in introductory biology or
zoology courses, it is often used as "THE" example of a digenetic
trematode. This species has been studied extensively by parasitologists, and
probably more is known about this species of digenetic trematode than any
other. The adult parasites reside in the intrahepatic bile ducts, produce eggs,
and the eggs are passed in the host's feces. After passing through the first
intermediate host (a snail), cercariae encyst on vegetation. The definitive host
is infected when it eats the contaminated vegetation. The metacercaria
excysts in the definitive host's small intestine, and the immature worm
penetrates the small intestine and migrates through the abdominal cavity to
the host's liver. The juvenile worm penetrates and migrates through the host's
liver and finally ends up in the bile ducts (view a diagram of the life-cycle). The
migration of the worms through the host's liver, and the presence of the
worms in the bile ducts, are responsible for the pathology associated with
fascioliasis.
Flukes - Trematodes
Protozoa - Coccidia
• Coccidia (coccidiosis) - Eimeria
Protozoa - Coccidia
• The diseases caused by these parasites are
referred to collectively as coccidiosis, and they
vary tremendously in virulence. Some species
cause diseases that result in mild symptoms
that might go unnoticed (i.e., mild diarrhea)
and eventually disappear, while other species
cause highly virulent infections that are
rapidly fatal.
Protozoa - Coccidia
A severe coccidiosis
infection in a small
animal
QUESTIONS?
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