Difference between revisions of "Category:Horse Nematodes"

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=== Small strongyles (Cyathostomins) ===
 
==== Morphology ====
 
'''Gross''':
 
*Small worms, <1.5cm long
 
*Small, shallow buccal capsule
 
 
'''Microscopic''':
 
*Buccal capsule shape
 
*Double row of leaf crowns
 
*Teeth may be present
 
 
==== Life-cycle ====
 
*Infection by ingestion of L3
 
*Larvae invade mucosa of large intestine
 
*Larvae may develop to L4 without interruption
 
*Cyathostomin larvae can arrest at EL3 stage
 
*L4 emerge into gut lumen and mature to adult worms
 
*Prepatent period 8-12 weeks (depending on species)
 
 
==== Pathogenicity ====
 
'''General''':
 
*Adult and larval worms are plug feeders, restricting the damage to more superficial mucosa
 
 
'''Cyathostominosis''':
 
*Initial infection (L3) → local inflammatory response
 
*Developing L4s can be seen as brown flecks in the mucosa
 
*They can be present in very large numbers (→ the so-called "pepper-pot lesion")
 
*Larval emergence throughout '''summer/autumn''' and plug-feeding of adults → major contributor to the "wormy" horse:
 
**Unthriftiness
 
**Poor coat
 
**Anaemia
 
**Diarrhoea)
 
*May be tens or hundreds of thousands of adults and millions of mucosal larvae present
 
*Emergence of massive numbers of previously arrested larvae in '''late winter/early spring''' → massive inflammatory infiltration → serious disease characterised by severe diarrhoea and/or weight loss (larval or Type 2 cyathostominosis)
 
  
  

Revision as of 21:54, 26 April 2010

Gastrointestinal Nematodes

Introduction

Parascaris equorum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Parascaris equorum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Parascaris equorum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Parascaris equorum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Strongylus - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Many nematode species occur in the equine gastrointestinal tract, although not all are of equal importance:


Stomach Small Intestine Large Intestine
  • Habronema (Draschia)
  • Trichostrongylus axei
  • Parascaris
  • Strongyloides
  • Strongylus species
  • Cyathostomins
  • Triodontophorus species
  • Oxyuris equi

Strongyles (Red worms)

The strongyles that occur in the horse can be divided on the basis of size into two groups

  • Large strongyles
    • Strongylus species (3 species; used to be widespread prior to the introduction of worm control programmes; now uncommon)
    • Triodontophorus species (common)
  • Small strongyles
    • Also known as Cyathostomins (preferred term), cyathostomes, trichonemes or small redworms
    • Cyathostomins (widespread, including 4 genera and over 40 species of worms)




General epidemiology of large and small strongyles

Strongylosis occurs in

  • Young horses
  • Adult animals (especially if overcrowding, poor hygiene)
  • Animals on permanent pasture

Sources of infection

  • Overwintered L3 on pasture
  • Many adult horses pass significant numbers of strongyle eggs throughout their lives
  • "Spring rise" in faecal egg output occurs in both breeding and non-breeding horses

Pattern of infection on pasture

  • Pattern of L3 on pasture is similar to gastrointestinal worms in cattle
  • Main difference is that the mare makes a major contribution to pasture contamination (c.f. cow)

Hypobiosis of cyathostomin larvae

  • Occurs throughout the year, but particularly in late summer/autumn
  • EL3 may remain arrested for years
  • Resumption of normal development can occur
    • seasonally in late winter/early spring
    • following removal of adult worm population via anthelmintic treatment

Larval cyathostominosis

  • Sudden onset diarrhoea and/or weight-loss
  • Diagnosis difficult, prognosis guarded
  • Generally in late winter/spring
  • Usually <5 years old
  • Sporadic, but increasing in incidence
  • Hyperglobulinaemia, especially IgG(T)
  • Hypoalbuminaemia
  • Leukocytosis
  • Sometimes peripheral oedema
  • Faecal egg-count low (disease caused by emerging larvae)
  • Larvae may be found in faeces or on faecal glove

Pathogenesis

Resumed development of massive numbers of larvae → subsequent emergence of bright red L4 → massive eosinophilic infiltration of mucosa → catarrhal and haemorrhagic colitis

Control of cyathostomin infections in horses

Anthelmintics

  • Only 3 chemical groups currently available
    • Avermectin/milbemycins
    • Benzimidazoles
    • Pyrantel
  • Resistance is an emerging problem (especially to benzimidazoles)

Target life-cycle stages

  • These are not all equally susceptible to each anthelmintic
  • Pyrantel is affective against
    • Adult worms in the lumen
  • Ivermectin or a one off administration of Fenbendazole is affective against
    • Adult worms and L4 in the lumen
  • Moxidectin or a 5 day course of Fenbendazole is affective against
    • Adult worms and L4 in the lumen
    • Developing and hypobiotic L3 in the mucosa

Egg reappearance period

  • This is the time from treatment until eggs reappear in the faeces. It is determined by
    • degree of activity against mucosal larval stages
    • persistency of anthelmintic treatment

Prevention of pasture contamination

  • The objective is to create safe grazing by preventing depostion of strongyle eggs onto pasture
  • Treat all grazing horses at intervals determined by
    • Egg reappearance time of chosen anthelmintic
    • Risk level
  • Treat all new arrivals and stable for 48-72 hours so that eggs are not passed onto pasture
  • Adopt strategy that will minimise risk of resistance developing (you may need to include tapeworm and stomach bots in your scheme)
  • No new eggs passed → no new L3 developing, however it is important to use epidemiological knowledge to predict how long existing L3 will survive as the pasture will not be safe for use before then
  • Remove faeces from paddocks at least weekly:
    • This markedly reduces dependence on anthelmintics
    • Increases available grazing
    • But is labour intensive and less effective in rainy weather
  • Examine faecal samples twice yearly to monitor effectiveness of your chosen strategy

Pasture management

  • Reserve clean grazing for nursing mares and foals
  • Rest pastures used the previous year until overwintered L3 have gone
  • Mixed or alternate grazing with cattle or sheep
    • These are refractory to most horse worms, except T.axei

Chemoprophylaxis of larval cyathostominosis

  • Needed if a horse is known to have grazed heavily contaminated pasture and may therefore be harbouring massive numbers of hypobiotic larvae
  • Fenbendazole treatment given daily for 5 consecutive days in autumn or winter will reduce the risk of clinical disease developing.