Larval cyathostomiasis - evidence for 50% death rate?

[soloequestrian]

Just interested!
I've been reading about this and come across the '50% mortality rate' in several articles (including peer-reviewed ones). I can find reference to three studies, all of which looked at case studies of very small numbers of animals (between two and 15), all of whom, as far as I can gather, were already showing severe illness symptoms. These were the three references: Giles, Urqhart and Longstaffe, 1985; Van Loon et al, 1995; Murphy et al, 1997. I can't access full papers at the moment so I'm wondering if I'm missing something, but the use of the statistic would seem to be slightly inappropriate because there is absolutely no measure of how many animals have a high burden of encysted redworm that doesn't actually cause clinical symptoms. Are there other studies out there that give a broader picture, or are we being encouraged to worm for encysteds on the basis of only this (rather flimsy?) evidence?

 

[Casey76]

Good overview here, with more referenced articles regarding the 50% mortality rate:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2751837/#!po=70.8333

It isn't the worm burden itself which causes the issue; it's when they emerge from the gut wall, basically destroying the permeability which can lead to chronic diarrhoea and proteinosis.

 

[soloequestrian]

Thanks - those are still case studies of small numbers of horses already showing clinical signs. It would be interesting to know how many horses actually carry a large burden of encysted larvae (an what constitutes a 'large' burden) and what the factors are that cause them to emerge en mass.... one paper said that animals with better acquired immunity tend to have higher levels of encysted larvae but didn't have any way of relating that to likelihood of a mass emergence. Another showed that most animals out of a sample of 20 had some level of encysted larvae but again didn't have any way to relate those to the likelihood of disease.
I'm interested because there never seems to be any discussion of how numbers of adult worms relate to numbers of encysted worms and/or factors that might lead to disease. There is just a general terror in the industry about encysteds, which I suspect keeps use of wormers higher than it needs to be.