Difference between revisions of "Strongyles"

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(Created page with 'This is a clinical term encompassing these superfamilies of bursate nematodes: Trichostrongyloidea Strongyloidea Ancylostomatoidea …')
 
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Their eggs are very similar and all contribute to [[Parasitic Gastroenteritis|parasitic gastroenteritis]].
 
Their eggs are very similar and all contribute to [[Parasitic Gastroenteritis|parasitic gastroenteritis]].
 +
 +
 +
=== 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.
 +
 +
 +
 +
  
 
[[Category:Nematodes]]
 
[[Category:Nematodes]]
 +
[[Category:Horse_Nematodes]]

Revision as of 21:58, 26 April 2010

This is a clinical term encompassing these superfamilies of bursate nematodes:

Trichostrongyloidea

Strongyloidea

Ancylostomatoidea


Their eggs are very similar and all contribute to parasitic gastroenteritis.


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.
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