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{{Taxobox

{{Taxobox

|name              =''Cyathostomins

|name              =''Cyathostomins

|species            =

|species            =

}}

}}

 

Also known as: '''''Trichonema spp.

| Also known as:

| '''Trichonema spp.

==Introduction==

==Introduction==

''Cyathostomins'' are a group of '''small strongyles'''. The majority of ''cyathostomins'' are similar in terms of both morphology and behaviour.  There are over 50 different species of small equine ''strongyle'', and they are of huge significance throughout the United Kingdom.  They commonly cause severe acute diarrhoea and colic.

''Cyathostomins'' are a group of '''small strongyles'''. The majority of ''cyathostomins'' are similar in terms of both morphology and behaviour.  There are over 50 different species of small equine ''strongyle'', and they are of huge significance throughout the United Kingdom.  They commonly cause severe acute diarrhoea and colic - [[Cyathostomosis]].

==Identification==

==Identification==

==Life Cycle==

==Life Cycle==

L1-L3 occurs within the envelope. The L3 then exits the sheath in the small intestine, and then concentrates within the '''Lieberkuhn's gland'''. At this stage they are known as EL3, and have two potential options.  Firstly, they may either become '''hypobiotic''', remaining dormant for several months to years.  This usually occurs Autumn-Winter.

L1-L3 development occurs on the pasture. The rate and extent of development and therefore infective 3rd stage larval challenge is directly affected by environmental conditions. At temperatures below 6 degrees centigrade minimal egg hatching and larval development occur (AAEP parasite control guidelines, 2013).

Or they may evolve directly and emerge 8-10 weeks later as LL3. They will then evolve into L4, at which stage they will emerge from a nodule.

Encysted, or hypobiotic larvae are unaffected by [[Anthelmintic Drugs]]. These encysted larvae represent around 50% of the total population.  After emergence of the cyst, L4 transforms into L5. They then transform into adults in the lumen.

Infective L3 larvae ingested by the grazing horse penetrate the large intestinal mucosa where they are  quickly (within a few days) encased in a fibrous capsule to become 'encysted'.  At this stage they are known as EL3, and have two potential options. Firstly, they may either become 'hypobiotic', remaining dormant for several months to years.  Hypobiosis usually occurs late autumn/ early winter in temperate climates. Alternatively EL3 may evolve directly into LL3 and then L4. After emergence of the cyst, L4 transform into L5 and then adults in the lumen of the caecum and colon. Importantly, since egg laying adults may not yet be present, a horse may be habouring large numbers of encysted small redworm despite a negative or low faecal worm egg count (FWEC).

If hypobiosis does not occur, the prepatent period is 6-14 weeks.

Highest egg shedding is in the spring months.  The larvae, which represent 90% of the population, are at maximal levels in the autumn.

Highest egg shedding is in the Spring months. The larvae, which represent 90% of the population, are at maximal levels in the autumn.

Only two anthelminitics have activity against encysted stages of small redworm, a single dose of moxidectin (MOX) or a 5-day course of fenbendazole (5d-FBZ). At 8 weeks post treatment with moxidectin EL3 stages are eliminated (Bairden et. al., 2006). Due to widespread resistance to fenbedazole a faecal egg count reduction test is recommended prior to using it for treatment of the encysted stages (Matthews, 2008). Killing of encysted mucosal larvae due to 5dy-FBZ has been associated with severe tissue damage, which clinically may correspond to reactions caused by synchronous mass emergence of fourth stage larvae (a condition known as larval cyathostominosis).  This effect did not occur after treatment with MOX (Steinbach et. al., 2006)   

 

 

 

 

|Vetstream = [https://www.vetstream.com/canis/search?s=nematode Nematodes]

 

 

 

[[Category:Strongyloidea]][[Category:Horse_Nematodes]]

[[Category:Strongyloidea]][[Category:Horse_Nematodes]]

 

[[Category:Expert_Review]]

[[Category:Expert_Review]]