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Parasite Matters Autumn 2021

As usual we’ll start by taking a look back at what the weather has been doing over the last few months. At the time of writing, the first half of August has been largely cool and damp, with considerable local variation across the country in rainfall levels, but temperatures generally below average across the board. July was warmer than normal for the whole country, but much drier in the normally wetter western side of the country. This all followed on from a warmer than normal and much drier than normal (except for the south east corner) June.

Weather Charts from Summer 2021 - courtesy of the Met office

So what does this mean for the parasites now, and what can we expect in the coming weeks?


  • Blowfly The NADIS risk alert remains at high for the majority of the country, with only the north and west of Scotland still on medium risk. The blowfly lifecycle thrives in warm humid conditions, and although July was dry for many, those areas that had some rainfall will have seen fly numbers increasing rapidly. The current cooler conditions will not significantly impede blowfly activity, so sheep farms should remain vigilant until average temperatures drop to single figures.
  • Ticks also thrive in warm humid conditions. The dry conditions may have limited tick activity in some areas, but if temperatures rise again into September, there will be enough moisture in the environment for another spike of tick activity.
  • Roundworm development in the environment speeds up in warm conditions, so the time taken to go from an egg landing on the pasture to an infective 3rd stage larva, waiting to be eaten, can be as little as two weeks. Although, some moisture is necessary for the eggs to hatch and larvae to develop, and in hot dry conditions larvae are at risk of desiccation, so are unlikely to survive for long on pasture. Therefore, many areas have had low pasture larval levels up to the end of July (i.e. low worm challenge), but this could change rapidly as cooler damp conditions are ideal for the larvae to survive.
  • GI worms – regular faecal worm egg counts will show when worm burdens are beginning to rise, and lambs or calves need to be treated. Don’t forget the Zolvix break dose for lambs – every farm every year.
  • Lungworm will also be a risk for grazing cattle. Youngstock that have not been vaccinated should be monitored closely and treated as required before housing time.
liver fluke snails in mud

  • Liver fluke disease with weather conditions generally warm and dry in June and July, the challenge overall is predicted to be low and to arrive later this season. However, there is likely to be huge variation between farms. Those farms where wet areas have remained (e.g. pond margins, ditches and boggy areas) will have seen mud snails thrive in the warm conditions; where there are mud snails there will be a fluke risk. This risk will not turn into a fluke challenge for grazing animals until the fluke have been through the life cycle stages in the snail. So, where are the fluke at the moment? Test Don’t Guess when it comes to fluke, and use the right active for the right stage of fluke in the right animals at the right time.

Parasite Matters Archive

Parasite Matters Summer 2021 (published June 2021)
Parasite Matters Spring 2021 (published March 2021)
Parasite Matters Autumn 2020 (published September 2020)

CLiKZiN™ Pour-On Suspension for Sheep contains the active ingredient dicyclanil and is indicated for the prevention of blowfly strike on sheep due to Lucilia sericata. Crovect™ Pour-On for sheep contains 1.25% (w/v) cypermethrin (cis:trans/80:20). For the treatment and control of headflies, tick infestation with a persistent efficacy of 10 weeks (the majority of ticks killed within 3 hours) and treatment of biting lice in sheep. Also for the prevention and treatment of blowfly strike in sheep. Combinex™ Oral Suspension contains 3.75% w/v levamisole hydrochloride and 5% w/v triclabendazole. Fasimec™ Duo 50 mg/ml + 1 mg/ml Oral Suspension for Sheep contains 50 mg/ml triclabendazoleand 1 mg/ml ivermectin. Fasinex™ 240 Oral Suspension for cattle contains 24% w/v triclabendazole. Fasinex™ 5% Oral Suspension contains 5% w/v triclabendazole. Flukiver™ 5% w/v oral Suspension contains 50mg/ml closantel. Supaverm™ Oral Suspension contains 5% w/v closantel and 7.5% w/v mebendazole. Zolvix™ 25mg/ml oral solution is a broad spectrum anthelmintic for the treatment and control of gastro-intestinal nematode infections and associated diseases in sheep including lambs, hoggets, breeding rams and ewes. Contains monepantel. Legal category: POM-VPS. Advice should be sought from the medicine prescriber prior to use. Use medicines responsibly ( Weather maps courtesy of the Met Office. For further information call Elanco Animal Health on +44 (0)1256 353131, or write to Elanco UK AH Limited, Form 2, Bartley Way, Bartley Wood Business Park, Hook, RG27 9XA. CLiKZiN™, Crovect™, Combinex™, Fasimec™ Duo, Fasinex™ 240, Fasinex™ 5%, Flukiver™, Supaverm™, Zolvix™, Elanco and the diagonal bar logo are trademarks of Elanco or its affiliates. © 2021 Elanco or its affiliates. PM-UK-21-0226