31 July 2026: Worm risk increases after rainfall
Updated 1 September 2026
Applies to England, Scotland and Wales
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This publication is available at https://www.gov.uk/government/publications/alerts-for-vets-emerging-and-endemic-disease-alert-system-eedas/31-july-2026-worm-risk-increases-after-rainfall
1. Situation
The recent dry conditions across much of Great Britain have meant reduced grass growth and reduced challenge from gastrointestinal nematode parasites that can affect grazing animals. As soon as we have some rainfall this will rapidly change with an increased risk of disease, as has been seen in some flocks already.
2. Details
Over the past few weeks we have seen very few cases of parasitic gastroenteritis or haemonchosis affecting sheep, based on submissions to our network of Veterinary Investigation Centres and Surveillance Pathology Partners.
Some areas have had rainfall in recent days, and we have already diagnosed haemonchosis in 2 flocks this week where deaths occurred. We expect to see negative impacts from other gastrointestinal nematode species too and egg counts will start to rise as the larvae on pasture develop to adulthood in the host sheep.
Using a combination of tools for regular monitoring of performance (daily liveweight gain), FAMACHA scoring of conjunctival membrane and faecal egg counts in sheep allows interventions to be timed accordingly to reduce risk of disease.
APHA are continuing to offer discounted differential fluorescence testing to detect Haemonchus eggs (test code TC0777, 5g of faeces required). Currently this is £21.20 per sample, please include the faecal egg count on the submission form if this has been undertaken to aid interpretation of results.
Send samples direct to APHA Carmarthen using our digital service, ADTS, for the fastest turnaround and reporting of results.
3. Further information
Read an overview of haemonchus contortus.
Find out more about how to test for diseases in farm animals.
Learn about the available Disease Surveillance Tests.
Explore guidance from SCOPS on https://www.scops.org.uk/internal-parasites/worms/.
Message sent from the Surveillance Intelligence Unit siu@apha.gov.uk.