• 28 January 2016

Don’t let your clients ignore Encysted Small Redworm says Zoetis

Zoetis is advising vets and SQPs to remind their clients that now is the time to treat their horses for encysted small redworm if they haven’t yet done so this winter. Moxidectin is the only licensed active for single dose control of encysted small redworm and is contained in only two products – Equest and Equest Pramox. However, a recent survey has shown almost one in three owners are still using the wrong products, putting their horses at risk.1

Encysted small redworm (ESRW) are the early stages of the small redworm enveloped within a fibrous capsule in the mucosa of the large intestine.2 In some animals, encysted early L3 larvae (EL3) enter a period of hypobiosis and these inhibited stages are thought to play an important role in the development of subsequent clinical disease.3 As yet, there is no definitive test for encysted small redworm and crucially, since egg-laying adults may not be present, a negative or low faecal worm egg count (FWEC) does not rule out the presence of encysted stages. Mass emergence of encysted larvae, often coinciding with warmer environmental conditions in the early spring, may cause a condition known as larval cyathostominosis, resulting in diarrhoea and colic, with a 50% mortality rate.4 

Every horse should receive an annual treatment to combat encysted small redworm, ideally during November/December and certainly before the spring arrives.3,5 It’s imperative that the correct wormer is used, but worryingly one in three horse owners are still struggling to get it right. Last year’s National Equine Health Survey showed that only 64% of those who specified how they treated for encysted small redworm had correctly used a wormer containing moxidectin and 7% had used fenbendazole. However, of the remainder, 22.5% had incorrectly used a wormer containing ivermectin, which does not treat for encysted stages and 6.3% had used products licensed for tapeworm only.1 

Given the prolonged mild conditions this winter and a recent cold snap, it is advisable to carefully discuss worming plans with your clients to ensure suitability for their horses’ circumstances. Small redworm worm eggs and larvae can survive on the pasture for longer when it’s warmer, increasing the window of opportunity for grazing horses to become infected. 6,7 

Wendy Talbot, veterinary surgeon at Zoetis, said: “The results of last year’s National Equine Health Survey are worrying. They strongly indicate that horse owners need proactive advice from their vet or SQP to ensure that they use a product licensed to treat for encysted small redworm, at the right time of year.” 

There are only two active ingredients licensed to treat for encysted small redworm: a single dose of moxidectin or a five-day course of fenbendazole. Resistance to fenbendazole is now widespread in the UK so a resistance test is recommended before using it.3,6 Moxdectin has high efficacy against adult small redworm as well as  luminal and mucosal larvae, including inhibited EL3.8

Equest and Equest Pramox are the only products available to treat for encysted small redworm in a single dose. Equest is an oral gel containing moxidectin for single dose control of roundworms - including encysted larval stages of small redworms, and bots. Equest Pramox is an oral gel containing moxidectin and praziquantel for single dose control of all three species