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
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
Merial Animal Health has produced a fascinating video which
shows the life cycle of the lungworm, and can be viewed here https://youtu.be/1cfOWNHS5Ko
"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
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