Larval cyathostomiasis (encysted redworm)

[soloequestrian]

Interested to know how many people have actually experienced a case of cyathostomiasis i.e. the horse becoming ill due to mass eruption of small red worm larvae from the gut.
I've been looking at this recently and the death rate tends to be expressed as 50% but that's in a very small number of horses that have already been diagnosed with the condition. In my understanding, fears about encysted red worms are what keep the rate of worming up high, which in turn is leading to ever increasing problems with resistance. There is some evidence that horses can live very happily with much higher worm burdens that we traditionally think - one paper suggesting that as high as 10,000 eggs per gram could be ignored.

Have we got it the wrong way on because our fears for our individual horses are much more powerful than the vague fear that we will run out of worming medicine completely if we don't change our management practices soon?

 

[JillA]

My friend who lectures in parasitology on equine courses maintains that unless you have a redworm burden to begin with, you have no reason to fear them being encysted, and therefore erupting. I have had clear FECs for a number of years so it is a problem I feel I can safely ignore.
Also she says it is a waste of chemicals worming while the weather is still frosty, as it won't kill any that are encysted - far more efficient to target them when they are out and active.

 

[soloequestrian]

Yes, I've always thought that about encysteds too - it doesn't make evolutionary sense for loads of them to be hanging around doing nothing in the gut wall if there is a nice competitor free gut there to be used! I think this might be part of the pattern - chemical worming is suggested as one of the risk factors for mass emergence (after about 2 weeks) and I have seen that happen in a student study, so I suspect there might be some signal for the encysted worms either from an 'empty' gut or from the drug itself. The horses I saw this happen to didn't have any obvious ill effects from the sudden high worm burden. It would be interesting if lots of people did an FEC about 3 weeks after worming for encysteds to see if this is a common pattern.