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  • Writer's pictureDr Emily Boreham MRCVS

Lungworm: the summer cough

Late June and July is peak 'Cough season' for lungworm. Any larvae picked up in Spring develop into adults and start to damage the sensitive lung tissue.

There's a lungworm for everyone:

  • Cattle: Dictyocaulus viviparus - often severe symptoms and significant problems.

  • Sheep: D.filaria - very mild in sheep, only animals with other health problems will show significant symptoms

  • Goats: D.filaria and M.capillaris - usually mild to moderate symptoms

  • Alpaca: D.viviparus and D.filaria - usually very mild or asymptomatic

  • Pigs: Metastrongylus - mild symptoms

  • Horses & Donkeys: D.arnfieldi - mainly affects donkeys.

Worm Lifecycle:

During the spring 'pre-patent' period the larvae spend months slowly maturing inside the body, often going unnoticed except the occasional cough. The infection will rarely show up in a WEC test at this time as very few larvae reach the poo.

Two to three months later in the height of the summer, the worms reach adulthood and start to produce eggs - the 'patent period'. This is when the trouble starts. The body massively reacts, flooding the lung with white blood cells, fluid and mucus.

Coughing all this up expels the new eggs and larvae out of the body - but spreads them efficiently accross the pasture ready to infect the next animal. Lots of larvae are swollowed after coughing, that's when we can find them in a WEC test.

On the positive, immunity lasts for years after an infection and the eggs and larvae are killed by a cold winter.


As with most infections, severity depends on parasite load and host immunity.

Young stock grazing their first year are most susceptible.

The signs will range:

  • Hacking cough

  • Cough exacerbated by exercise

  • Increased respiratory rate

  • Weight loss

  • Sudden drop in milk yield

Most animals will get better by the end of the summer, but some will develop secondary pneumonia:

  • Lethargy and weakness

  • Off food

  • High temperature

  • Cough, nasal discharge

  • Laboured breathing

  • Cyanosis - blue gums and tongue

  • Death

These animals have severe damage to their lung tissues and will be under weight and fail to thrive for many months even after treatment. Some are permanently damaged and will always struggle.


There's little you can do to monitor your herd for lungworm until the parasite hits that productive patent phase. We need the worms to reach adulthood and start releasing their larvae and eggs. As soon as these get swollowed they'll appear in the faeces.

A normal WEC floatation will pick up larvae and larvated eggs if the infestation is heavy. A much better technique is to use a baermans filter where the larvae swim through a membrane and collect together:

For you DIY worm egg counters out there - you can easily do this at home. Put 20-30g of poo in a coffee filter or muslin cheesecloth, hang in champagne flute filled with warm water. Leave for atleast 4 hours. Pour everything away except the last drop in the very bottom of the flute and examine that under your microscope:


Now for some good news!

Lungworm is easily treated by our normal wormer choices:

  • Ivermectin

  • Moxidectin (cydectin)

  • Eprinomectin (eprinex)

  • Albendazole

Levamisole is less effective against larvae so always do two treatments two weeks apart for this wormer.

Resistance is rarely reported.

In Summary:

  • Watch out for summer coughs

  • Severity: cattle > goats > donkeys > sheep > alpacas > pigs > horses

  • Treat before pneumonia sets in

  • Diagnosis is best with the extra Baermans technique

  • Treat with your usual wormer

  • Immunity is long lasting

Our routine WEC at the Smallholders Worm Advice Service includes a Baermans screen for lungworm.

Now you just have to choose how best to use that Champagne flute....

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