1. Internal Parasites in Horses
Created by: Tracey Hoffman Topic #3080

2. Parasite
Organism that lives off another organism at the expense of the host

3. Major Equine Parasites
Strongyles
Roundworms
Bots
Pinworms

4. Strongyles Includes both large and small strongyles Most common
Commonly referred to as bloodworms
Because of color after it ingests blood from host animal

5. Life Cycle Larvae develop to infective stage within one week
Larvae crawl up blades of grass and are ingested by the horse
Once ingested, larvae travel through the digestive system to the large intestine
S. vulgaris migrate to the anterior mesenteric artery

6. Life Cycle
S. endentatus to the liver and flank area
S. equinus migrate to the liver and pancreas
Adult large strongyles live in the cecum and large intestine
Eggs are laid in the cecum and large intestine and passed through the feces
Superior mesenteric artery

7. Adult Strongyle Damage
These worms are aggressive feeders
After feeding, move to a fresh site leaving a bleeding crater
Craters ulcerate and heals, leaving scar

8. Large Strongyles in Mesenteric Artery
Large strongyles can live in mesenteric artery, which supplies blood to the intestine
Inflame artery wall
Create blood clots that interfere with oxygen and nutrients to/from the intestine
Leads to severe and often fatal colic

9. Small Strongyles Also called cyathostomes Cause under-performance
Loss of condition
Feed inefficiency
Predisposition to secondary diseases
Are extremely prolific
Emerge from lining of intestines and leave an ulcerated gut wall

10. Roundworm Life Cycle
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)
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

11. Roundworm Life Cycle Adult roundworms in small intestine
Eggs are laid in the small intestine
Eggs are excreted in feces
Larvae develop to infective 2nd state eggs within two weeks
Emaciated infected foal
Adult roundworms clustered in ruptured small intestine

12. Roundworms Adult roundworms are visible to the eye
Roundworm larvae migration through the lungs and liver is most dangerous
Often causes foal pneumonia – potentially fatal

13. 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

14. Bot life Cycle Pupae form in loose soil
Adult bot fly emerges from pupa in 3-10 weeks. Female posterior is long and pointed to deposit eggs.
Common bot 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

15. Bot life Cycle
Throat bot fly (G. nasalis) lays eggs on hairs around side and back of mouth. Eggs are ingested with food and water.
Nose bot fly (G. hemorroidalis) lays eggs around nose and mouth. Eggs ingested with food and water.
Larvae of bot fly cluster on linings of stomach and proximal duodenum

16. Bot life Cycle Larvae passed in feces Common bot fly larva
Throat bot fly larva

17. 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 lvermectin or Mexidectin 1 month after first frost and in spring to eliminat larvae in stomach

18. Pinworm Life Cycle
Sticky eggs will adhere to walls, fences, bedding, and will be found in water or feed
Larvae develop into infective stage within the eggs
Infective larvae are ingested by the host. Larvae travel through digestive system to the cecum and large intestine where they mature in four or five months.

19. Pinworm Life Cycle
Adult pinworms reside in the lumen of the cecum and large intestine
Adult female crawls to the skin around the anal area to deposit eggs in clusters

20. 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