(cyathostomes spp)
Cyathostomes spp infestation in small intestine The most common worm is the Small Redworm (cyathostomin spp) which can lead to encysted small Redworm disease if untreated.
When ingested, the larvae burrow into the lining of the intestines. They either develop and re-emerge to continue the life cycle, or stay in a state of hibernation in the intestinal lining-hypobiosis.
Hypobiotic larvae can all emerge at once causing severe damage to the intestinal wall which can cause weight loss, diarrhoea, shock and death.
The Typical Life Cycle of Small Strongyles
- The horse ingests grass which has stage L3 larvae on it.
- The larvae enter the large intestinal mucosa. There it either undergoes hypobiosis (similar to hibernation) and emerges as L4 later or immediately emerge as L4. There is a high damage risk of large numbers of encysted L4 emerging from mucosa at same time
- The L4 larvae develop and lay eggs
- These eggs pass out in faeces
- The eggs on the faeces develop first into L1, then into L2 and finally into L3 larvae
- The larvae move onto the grass
- The horse ingests grass and the cycle starts again
Small strongyles- treatment options and resistance
| Fenbendazole | Pyrantel | Ivermectin | Moxidectin | Praziquantel | ||
|---|---|---|---|---|---|---|
| Cyathostomins | Adults | Resistance is common Should only be used with supportive FECRT results |
Resistance reported FECRT should be performed to confirm efficacy | Complete resistance considered uncommon but shortened egg reappearance periods are now a common finding | Shortened egg reappearance periods are now being reported and resistance recently reported in the UK | Not indicated |
| Encysted larvae | 5-day course Resistance is common and use for 5 consecutive days does not overcome it Should only be used with supportive FECRT results |
Not indicated | Not indicated | No reports of resistance atthe encysted larval stages1 | Not indicated |
1 Larvicidal efficacy of moxidectin ranges from about 20 to 70% against Early Third Stage Larvae (EL3s), and 50-80% against developing larvae (late L3s and mucosal L4s) (Nielsen, 2022).
Source: Canter Guidelines
Remains effective for indicated use
Resistance emerging or suspected
Some resistance reported – FECRT should be performed
Resistance common – should only be used with supportive FECRT results
Not indicated for use for treatment
