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Don’t ignore the threat of lungworm


Animal health advisers and their clients should be alert to the threat of lungworm this summer according to Merial Animal Health Veterinary Adviser Sioned Timothy.

Although the clinical disease is typically seen in mid-late summer, proactively managing pasture larvae levels throughout the grazing season is key if the risk of disease is to be minimised. Maintaining a fine balance between exposure and immunity is critical to the prevention of clinical husk.

Anthelmintics or vaccination are useful tools in achieving this and can be deployed strategically following advice from a vet or animal health advisor, taking into account farm level risk factors and management practices.

At turnout, low levels of overwintered larvae are present on pasture grazed the previous year. These levels decline as the year goes on, decreasing significantly by early summer. However, studies have shown that up to 10% of cows may be sub-clinical carriers of Dictyocaulus viviparus and contribute low numbers of larvae to this pasture contamination1.

Once the infective larvae are consumed by grazing cattle they penetrate the intestinal wall and migrate through lymphatics and blood vessels, reaching the lungs after approximately seven days. The larvae then mature as they travel through the airways, and adult worms are present in the trachea approximately 25 days after infection.

Hatched larvae are then coughed up and swallowed, before being passed out onto pasture in the faeces.  A low dose infection with 200 larvae can lead to around 70 adult worms which can result in 2.5 million infective larvae on the pasture by 30 days after ingestion2. This shows how heavy worm burdens, capable of causing severe clinical disease, can establish quickly.

The survival and infectivity of larvae on the pasture is affected by a number of environmental factors; with optimal conditions hastening development. Larvae on pasture rapidly dry out in hot dry weather, but can survive within the dung pat.  Their dispersal is facilitated by heavy rain, and the pilobolus fungus also plays an important role as it can propel larvae up to 3 metres away from the dungpat, as it expels its own spores.

If young or naïve cattle are exposed to high pasture challenge without prior vaccination or sufficient low level exposure to have developed immunity, clinical disease will be seen. In older animals that have an established level of immunity low levels of pasture challenge will serve to boost this, but in the face of heavy, uncontrolled challenge, outbreaks of severe potentially fatal  disease can also be seen in adult cows.


August and September are the most common months for outbreaks of the disease, but the threat of lungworm can continue until November or even December, particularly in mild and wet conditions.

Regardless of age, lungworm should always be suspected in cattle coughing at grass. There are a variety of diagnostic techniques available through vets. Where an outbreak of husk occurs, whole herd treatment with a suitable anthelmintic is indicated.

Ms Timothy says: "Producers should be aware of the risk posed by lungworm to all grazing cattle, and ensure that a control strategy is in place at turnout and throughout the summer. The effect of lungworm at its most extreme is death, but even in cases where this does not occur, lungworm can cause clinical disease of varying severity, affecting the productivity of the cattle. It's important to act swiftly in order to prevent major losses."

A study published in 2011 looked at two outbreaks of lungworm in dairy cows and reported losses of €159 per head in one case and €163 in another3. This resulted from reduced milk production, impaired fertility and diagnostic and treatment costs. In another outbreak where 50% of the adult milking herd exhibited signs of respiratory disease, the average daily milk yield increased from 23 kg to 30kg per day following treatment with eprinomectin, highlighting the scale of potential production losses4.

Lungworm diagram

Merial Animal Health has produced a fascinating video which shows the life cycle of the lungworm, and can be viewed here

"In dairy cows, EPRINEX® (eprinomectin) provides persistent activity for up to 28 days and has a zero milk withhold. It provides a cost-effective treatment for lungworm lessening the impact of the disease on profitability," says Ms Timothy.



1. Eysker M, Classens EW, Lam TGM, Moons MJ, Pijpers A (1994) The prevalence of patent lungworm infection in herds of dairy cows in the Netherlands. Vet Parasitol 53 (3-4) 263-267

2. Vercruysse J, Janssens PG, Vercruysse J, Jansen J (1989) Ductyocaulosis. In: Worms and Worm Diseases pp 210-222 Samson Stafleu, Alphen aan den Rijn/Brussel

3. Holzhauer M,  van Schaik G, Saatkamp HW, Ploeger HW (2011) Lungworm outbreaks in adult dairy cows: estimating economic losses and lessons to be learned. Vet Rec 169 (19) 494-

4. Wapenaar W, Barkema HW, Eysker M & O'Handley R (2007) An outbreak of dictyocaulosis in lactating cows on a dairy farm. JAVMA 231 (11) 1715 -1718


Eprinex 433 x 125


Merial-Sanofi_Logo_rgb EPRINEX® 0.5% w/v Pour-On for Beef and Dairy Cattle contains eprinomectin. EPRINEX® and the steerhead® logo is a registered trademark of Merial Ltd. © Merial 2016. All rights reserved. Legal Category: POM-VPS (UK), LM (Ireland). Advice on the use of these or alternative medicines must be sought from the medicine prescriber. For further information refer to the datasheet,  contact Merial Animal Health Ltd, CM19 5TG, UK, or call the Merial Customer Support Centre on 0800 592699 (UK), 1850 783 783 (Ireland).

Use medicines responsibly.