HORSE WORMS

Horses are commonly infected with gastrointestinal nematodes, trematodes and cestodes.

1. Gastronintestinal Nematodes (Round Worms)

The most important worms found in horses are:

  • Large strongyles (Strongylus spp.)
  • Small strongyles (Cyathostomes)
  • Large roundworms (Ascarids)

Other less common worms are listed in Table 3.1 and include:

  • Intestinal threadworm (Strongyloides westeri)
  • Stomach worms (Trichostrongylus axei)
  • Pinworm (Oxyuris equi)

2. Trematodes (Flukes)

  • Liver fluke (Fasciola hepatica) is an important parasite of horses in certain areas where conditions are suitable for the intermediate host, an aquatic snail.
  • Stomach fluke (such as Paramphistomum spp or Calicopheron spp) occasionally cause disease, mainly in coastal areas.

3. Cestodes (Flatworms)

  • Tapeworm (Anoplocephala perfoliata)

4. Bots (Gastrophilus spp.)

  • Bots are the larvae of a fly not worms.  They will not be detected during a WEC.

5. Coccidia (Eimeria)

  • Coccidia are microscopic protozoal parasites not worms..

 

COMMON HORSE WORMS (Table 3.1)

Common NameScientific Name
Most Important Roundworms  
Large strongyles Strongylus spp.
Small strongyles Cyathostominae
Large roundworms Parascaris equorum
Intestinal threadworm Strongyloides westeri
Stomach worms Trichostrongylus axei
Pinworms Oxyuris equi
Cestoda (tapeworm)  
 Tapeworm Acocephalia perfoliata
Trematodes (flukes)  
Liver fluke Fasciola hepatica

Source: Beveridge, I., Gasser, R., Sangster, N. (2015). Horses. In: Beveridge, Ian, and Emery, David, (eds.) Australasian Animal Parasites: Inside & Out. Australian Society for Parasitology, pp. 792-841

 

GUIDE TO WORM EGG COUNTS IN HORSES – Table 3.2

Worm egg count (epg)Interpretation / comments
0 - 100* A good result. There would be few situations where you would contemplate drenching at this level. Check egg counts in 4-6 weeks after significant rain.
100 - 200* Low egg count result. Treatment may be required in younger animals or animals under stress. If not treated check egg counts in 4 weeks time.
200 - 500* Moderate egg count result. Treatment would be advisable in most cases.
Above 500* High egg count result. Treatment required.

*strongyle eggs per gram of faeces (epg)

Source: Anne Oakenful, (2008). Revised by Stephen Love, September 2013. NSW DPI Faecal Egg Counts for Worms Manual.