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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]]