Parasitology - Equine PGE Flashcards
What is the most important nematode that causes equine parasitic gastro-enteris (PGE) compex?
Strongylus species - ie., Strongyles also known as RED WORMS
What are parasites that invade the horse’s large intestine (the large ascending colon)?
Large strongyles aka large redworms:
- Strongylus vulgaris*
- S. edentatus*
- S. equinus*
- Triodontophorus spp.*
Small strongyles aka small redworms:
- Cyathosomins* (aka trichonemes) of which there are > 40 species;
- Oxyuris equi* aka “pinworms” - invades caecum, large intestine & rectum
What is the name of the PGE caused by large red worms / large strongyles?
What parts of the pathogenesis do the different species of Strongylus (large red worms) share?
* Strongylosis*
Common Aspects of Pathogenesis:
Horse eats grass infested with L3 stage of Strongylus - can be S. vulgaris, S. edentatus, S. equinus or Triodontophorus.
Larvae pass down the intestinal tract & penetrate intestinal mucosa. At this larval stage, S. vulgaris is the most pathogenic, potentially damaging the cranial mesenteric artery & resulting in thrombosis & colitis.
Then, depending on the species, will go through different migrations & pre-patent periods.
What is the condition caused by small red worms / small strongyles in the large intestine?
Cyathosominosis
Type I & more-serious Type II
What is the morphology of the large red worms/large strongyles,
Strongylus vulgaris
S. edentatus
S. equinus
?
- *Gross**:
- Stout, 1.5-5 cm long
- Large buccal capsule
- Bursa visible to naked
eye in male
Micro (buccal capsule):
-
Double row leaf
crowns(see photo of S. vulgaris)
- Teeth (0,2,3 or more) -
not in S. edentatus - Dorsal gutter (channel
for enzymatic secretions)
All the large red worms (large strongyles) that cause Strongylosis in the large intestine (colon) of the horse share the common initial pathogenic pathway of being ingested at L3 stage by horses eating grass.
The larvae enter the intestinal tract, penetrating the intestinal mucosa, before they take different paths.
Describe the path of Strongylus vulgaris.
S. vulgaris, unlike S. edentatus or S. equinus, is potentially highly pathogenic at the larval stage, not just the adult stage. From the ascending colon, the larvae:
→ migrate into anterior (cranial) mesenteric artery over 2 weeks → burrow into intersection of artery & aorta to form verminous endarteritis lesion over 3-4 months → migrate back down via anterior mesenteric artery & moult → bore hole into descending colon & exit as adults over 6-8 weeks
As adults, they become plug feeders with their large buccal capsules, penetrating down into the muscularis layer and blood vessels. They leave circular bleeding ulcers that can lead to anaemia if there are many.
PPP = 6-7 months
NB: endarteritis is the inflammation of the intima of one or more arteries
All the large red worms (large strongyles) that cause Strongylosis in the large intestine (colon) of the horse share the common initial pathogenic pathway of being ingested at L3 stage by horses eating grass.
The larvae enter the intestinal tract, penetrating the intestinal mucosa, before they take different paths.
Describe the path of Strongylus edentatus.
S. edentatus (without teeth) are relatively **non-pathogenicas larvae(unlike S. vulgaris). Their larval migration takes them to roomy tissue like theliver & mesentary** that can withstand more damage than the cranial mesentery artery as with S. vulgaris.
After entering the large intestine (ascending colon), S. edentatus larvae:
→ migrate via hepatic portal system to liver → form nodules in liver → moult → exit liver via peritoneum → migrate via periotoneum back to large intestine → exit as adults
PPP = 11-12 months
All the large red worms (large strongyles) that cause Strongylosis in the large intestine (colon) of the horse share the common initial pathogenic pathway of being ingested at L3 stage by horses eating grass.
The larvae enter the intestinal tract, penetrating the intestinal mucosa, before they take different paths.
Describe the path of Strongylus equinus.
The larvae of S. equinus is relatively non-pathogenic, unlike S. vulgaris. Like S. edentatus, the larval migration of S. equinus is through roomier tissue such as the liver that is able to withstand damage better than the cranial mesenteric artery as in the case of S. vulgaris. After entering the horse’s ascending colon, the larvae:
→ crosses peritoneal cavity from intestine to liver → “wanders around” liver before returning to large intestine via peritoneal cavity again → exits as adult
PPP = 9 months
Recap where the larvae of the large redworms go to migrate and moult after they enter the horse’s large intestine?
Strongylus vulgaris
S. edentatus
S. equinus
Strongylus vulgaris - cranial mesenteric artery to junction of artery & aorta, then back to colon via mesenteric artery
S. edentatus - hepatic portal system to liver then back to colon via peritoneum
S. equinus - peritoneal cavity to liver then back to colon via pernitoneal cavity
All the large red worms (large strongyles) that cause Strongylosis in the large intestine (colon) of the horse share the common initial pathogenic pathway of being ingested at L3 stage by horses eating grass.
The larvae enter the intestinal tract, penetrating the intestinal mucosa, before they take different paths.
Describe the path of Triodontophorus.
Unlike the other large red worms, Strongylus vulgaris, S. edentatus & S. equinus, Triodontophorus is non-migratory. Instead, it just stays in the large intestine and moults there into an adult, where it feeds in “herds”.
After entering the large intestine of the horse, the larvae:
→ moves around wall of large intestine → moults to L4 → exits as adults
As adults, it causes superficial damage with its small buccal cavity, but feeds in herds, leaving large large, superficial ulcers several cm across that leave scars after they heal.
PPP = 2-3 months
Aside from large redworms (large strongyles), what other nematode types cause PGE in the horse’s large intestine?
Small redworms (Cyathosomins, aka Trichonemes)
Pinworms (Oxyuris equi)
What is the morphology of the small red worms, also known as Cyathostomins or Trichonemes? How do they differ in appearance from the large strongyles?
They look a lot like the large strongyles/red worms, but they are smaller, less than 1.5 cm (large redworms are 1.5-5 cm long).
They have small, shallow buccal capsules with double row of leaf crown and possibly teeth.
See photo.
What happens to the small redworms, Cyathostomins, after they enter the large intestine of the horse as L3 with grass?
Cyathstomins are confined to the gut wall, but can take two life-cycle routes:
- L3 can become arrested in gut wall for several months → moults to L4 → emerges as adult in gut lumen
OR
- L3 moults to L4 → emerges as adult in gut lumen
PPP = 8-12 weeks
Why would a small redworm, Cyathostomins aka Trichoneme, become **arrested at L3 for several months or years **in the large intestine of the horse rather than moult from L3 to L4 to adult in its normal 8-12-week PPP?
Similar to ostertagia in calves, the larvae become arrested in the gut wall (potentially for years) if they were ingested in late summer or early autumn. They become hypobiotic throughout the winter and emerge in late winter or early spring, and this is quite harsh for the horse.
What is different about the hypobiotic larval stage of Cyathostomins compared with Ostertagia?
Cyathostomins, aka small red worms, become arrested as L3 and they can stay hypobiotic for years.
Ostertagia become arrested at L4 and typically are hypobiotic until the next grazing season.
What is the name of the condition caused by Cyathostomins aka Trichonemes aka small red worms, and what are the different types?
Cyathostominosis.
Type I Cyathostominosis:
- Initial infection (L3) → local inflammation
- larval emergence in summer/autumn
+ plug-feeding adults = wormy horse
- *Larval / Type 2 Cyathostominosis:**
- larval emergence (late winter/early spring) → severe diarrhoea → severe weight loss
NB this is like ostertagia in calves & sheep, which can accumulate L3 that become hypobiotic & then attack harshly as adults
When do small redworms become plug feeders?
Small redworms, Cyathostomins, are plug feeders as larvae & adults.
The large redworms Strongylus vulgaris and Triodontophorus are only a plug feeders as adults.
What are the clinical signs of Cyathostominosis Type I, aka “wormy horse”? How many adult and larval worms are present?
Unthriftiness, poor coat, anaemia, diarrhoea
10s or 100s of thousands of adults and millions of mucosal larvae present.
What are the clinical signs of Cyathostominosis Type II, aka “wormy horse”? How many adult and larval worms are present?
Massive inflammatory infiltration, serious diease characterised by severe diarrhoea &/or weight loss
In what age of horse does Strongylosis typically occur? In what type of environment?
Young horses on permanent pasture
Adult horses especially if there is overcrowding or poor hygiene
What are the sources of Strongylosis infection?
Like ostertagia, L3 on pasture, spring rise, overwintered L3
In what age of horse does cyathostominosis typically occur?
Young horses less than 5 years old.
The pinworm - aka Oxyuris equi - also attacks the large intestine in the horse, causing PGE. What is the morphology of the pinworm?
Females large: <10 cm long, white, with thin, pointed “pin-like” tails (see photo)
Males small: <1 cm long, difficult to see
Where are the preferred targets of the pinworm in the horse GIT?
Caecum
Large intestine (colon)
Rectum
