KEY
Note Taking Guide
Topic: 3189D
Internal Parasites in Horses
Created by: Tracey Hoffman
Topic #3080
Parasite:
Organism that lives off another organism at the expense of the host
Major Equine Parasites
1. Strongyles
2. Roundworms
3. Bots
4. Pinworms
Strongyles
-
Includes both large and small strongyles
- Most common
- Commonly referred to as bloodworms
- Because of color after it ingests blood from host animal
- Life Cycle
A. Larvae develop to infective stage within one week.
B. Larvae crawl up blades of grass and are ingested by the horse.
C. Once ingested, larvae travel through the digestive system to the large
intestine.
S. vulgaris migrate to the anterior mesenteric artery.
S. endentatus to the liver and flank area.
S. equinus migrate to the liver and pancreas.
D. Adult large strongyles live in the cecum and large intestine.
E. Eggs are laid in the cecum and large intestine and passed through the
feces.
F. Superior Mesenteric Artery
Adult Strongyle Damage
1. These worms are aggressive feeders
2. After feeding, move to a fresh site leaving a bleeding crater
3. Craters ulcerate and heals, leaving a scar
Large Strongyles in Mesentaric Atery
1. Large strongyles can live in mesentaric artery, which supplies blood to
the intestine
2. Inflame artery wall
3. Create blood clots that interfere with oxygen and nutrients to/from the
intestine
4. Leads to severe and often fatal colic
Small Strongyles
1. Also called cyathostomes
2. Cause under-performance
loss of condition
feed inefficiency
predisposition to secondary diseases
1. Are extremely prolific
2. Emerge from lining of intestines and leave an ulcerated gut wall
Roundworm Life Cycle
A. Host foal ingests infected eggs from contaminated environment and/or
feed. Eggs pass through oral cavity to the stomach and into the small
intestine. (Solid Arrows)
B. Eggs hatch in intestine and migrate through the liver to the lungs via the
circulatory system. Larvae then travel to the pharynx and are swallowed
(tracheal migration shown by the interrupted arrows). Larvae mature to
adult state in the small intestine.
C. Adult roundworms in small intestine.
1
D. Eggs are laid in the small intestine.
E. Eggs are excreted in feces.
2
F. Larvae develop to infective 2nd stage eggs within two weeks.
G. Emaciated infected foal.
3
H. Adult roundworms clustered in ruptured small intestine.
Roundworms
- Adult roundworms are visible to the eye
- Round worm larvae migration through the lungs and liver is most
dangerous
- Often causes foal pneumonia – potentially fatal
Large Roundworms
- Most common in young horses
-
Intestinal infections may show no clinical signs
- Can decrease gut motility
-
Intestinal impactions from clustered roundworms may cause rupture to the
intestine and produce peritonitis
Bot Life Cycle
A. Pupae form in loose soil.
B. Adult bot fly emerges from pupa in 3-10 weeks. Female posterior is long and
pionted to deposit eggs.
A. Common bog fly (G. intestinalis) lays eggs on leg hairs. Eggs must be licked
to hatch larvae. After ingestion, larvae tunnel in epithelium of tongue and
form pockets between upper molars. One month later, larvae migrate to
stomach or duodenum.
B. Throat bot fly (G. nasalis) lays eggs on hairs around side and back of mouth.
Eggs are ingested with food and water.
C. Nose bot fly (G. hemorroidalis) lays eggs around nose and mouth. Eggs
ingested with food and water.
D. Larvae of bot fly cluster on linings of stomach and proximal duodenum.
E. Larvae passed in fecus.
F. Common bot fly larva.
G. Throat bot fly larva.
Bots
- Eggs are yellow in color
- Eggs are difficult to remove
- Each female bot fly may lay as many as 1,000 eggs
- Removal of eggs on hair coat when present is essential
- Use Ivermectin or Moxidectin 1 month after first frost and in spring to
eliminate larvae in stomach
Pinworm Life Cycle
A. Sticky eggs will adhere to walls, fences, bedding, and will be found in water
or feed.
B. Larvae develop into infective stage within the eggs.
C. Infective larvae are ingested by the host. Larvae travel through digestive
system to the cecum and large intestine where they mature in four to five
months.
D. Adult pinworms reside in the lumen of the cecum and large intestine.
E. Adult female crawls to the skin around the anal area to deposit eggs in clusters.
Pinworms
- Major sign is horse rubbing his tail or rear quarters on any available surface
- Caused by females depositing eggs
- Eggs are pale yellow to cream colored
- Contain fluid
- Need a microscope or hand lens to view them
- Cleanliness is essential prevention
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