BEVA and Equine Infectious Disease Surveillance (EIDS) have partnered to address several misconceptions about small redworm, a parasite that continues to pose serious risks to horses across the UK. Seasonal patterns mean that late autumn and early winter represent a particularly high-risk period for larval cyathostominosis. Vigilance, accurate interpretation of diagnostics and consistent reporting are therefore essential. Read on for an overview of key myths, the realities behind them and how vets can use the latest surveillance tools to support better clinical decisions.
Myth one: “A negative FEC reliably rules out a clinically significant cyathostomin burden.”
Reality: Routine faecal egg count (FEC) tests only detect egg-laying adult worms. Encysted larval stages of small redworm (cyathostomins) reside within the gut wall and do not produce eggs, so they are invisible to FEC.
Implication for vets: FEC should not be used alone to rule out risk of larval cyathostominosis nor to decide that no treatment is required, especially in late autumn/early winter, or in horses with high risk factors (i.e. stocking density, history of low-level shedding but potential for larval accumulation).
Myth two: “Cyathostomin infection is primarily a problem in young stock. Adults are generally protected.”
Reality: While younger horses may be at higher risk, adult horses remain fully susceptible to cyathostomin infection, including encysted larvae. Mature animals can accumulate significant burdens and may develop larval cyathostominosis.
Implication for vets: Do not assume older horses are “safe.” Worm control and monitoring programmes should include adult horses, especially in herd contexts, and risk assessments should consider management, pasture contamination, history of worming and local epidemiology, not just age. Helpful websites can be used to aid clinical decision making.
Myth three: “There is nowhere for me to report clinical cases of small redworm or strongyle”
Reality: This may have been the case before late 2024 but EIDS now oversees RedWatch - a bespoke surveillance initiative focusing on small and large strongyle disease occurrences in the UK. It gathers essential case data to better understand disease patterns and risk factors.
Implication for vets: RedWatch will allow veterinary surgeons to report and gain insights into the occurrence of small strongyle related clinical disease. In addition, although large strongyles are often detected during post-mortem examinations (PME) and may be captured in the pathology section of EIDS’s equine quarterly disease surveillance report, RedWatch will also allow additional reporting of large strongyle cases. Read report cases here.
Myth four: “Antibody testing provides a precise indication of the encysted larval burden.”
Reality: Serological tests developed for cyathostomins do not directly quantify encysted larval burden, and results must be interpreted carefully and with clinical context. However, they do provide information on exposure to the parasite and can help in risk assessment.
Implication for vets: Use serological tests as part of a broader diagnostic protocol, not as standalone “proof” of current encysted larval load. They can guide decisions, especially in low-shedding horses or those with low FECs, but should be combined with risk-assessment, pasture history, prior anthelmintic treatment, and clinical context before deciding on larvicidal treatment.
Myth five: “Choice of anthelmintic is not critical because standard products cover all life stages.”
Reality: Anthelmintic efficacy against Cyathostomin (small redworm) varies markedly depending on life-stage. Not all commonly used wormers will kill encysted larval stages. If a wormer lacks larvicidal activity, treating only with that product risks leaving a potentially dangerous encysted burden unchecked.
Implication for vets: Prescribing decisions must be deliberate and informed. When the goal is to address encysted larvae, for example late in grazing season or in autumn/winter, select a product with proven efficacy against those stages (for instance a licensed larvicide) rather than defaulting to an adult-targeting wormer. Use the risk-assessment framework and guidance in the CANTER Guidelines to decide if, when and how to treat. Doing so helps avoid unnecessary worming and helps preserve anthelmintic efficacy by avoiding overuse or misuse.
Robust surveillance and timely reporting play a central role in protecting equine health. By engaging with RedWatch and contributing case information, equine vets can strengthen the national understanding of small redworm related disease and support more accurate risk modelling. Your clinical observations, diagnostic choices and reporting efforts are vital to improving outcomes for horses and to the long-term stewardship of anthelmintic efficacy.