Be alert to the effects of lungworm in Ireland's moist climate

HERD HEALTH SERIES: Maura Langan, Commercial and Technical Manager (Large Animal) at Norbrook.

Lungworm is one of the most disruptive parasites for cattle on Irish farms, and it’s a common problem on many farms at this time of year. 

With Ireland’s mild and moist climate, conditions are ideal for lungworm to thrive on pasture, and our production systems rely on heavy grazing during the summer months.

Development of lungworm larvae passed out onto pasture in the faeces is affected by the weather. Infection can be rapid if warm (20°C) and humid conditions prevail. 

As a result, we typically expect to see clinical cases occurring late July or into August. Larvae may be dispersed from the dung pat by a fungus or by the splashing effects of rain. 

This means that pastures can become contaminated with infective larvae very quickly, and peaks in lungworm infection commonly occur when heavy rain follows a dry spell, as we have seen in recent weeks.

Lungworm affects both young and adult animals and can result in long-term effects or even death. The disease is caused by parasitic worms that invade cattle lungs after ingesting infective larvae while grazing. 

Once in the body, these larvae travel through the animal’s system and mature in the airways, where they trigger inflammation and respiratory distress. 

The cycle from ingestion to symptoms can be quite short, making lungworm one of the few parasitic diseases that can present dramatically and unexpectedly, even in well-managed herds.

The severity of infection and development of the disease throughout the herd is variable and unpredictable, making lungworm particularly challenging to control. 

First-season calves are completely naïve, and if exposed to large numbers of lungworm, the resulting clinical infection can be devastating. Young stock will require repeated moderate exposure to develop protective immunity, but the persistency of that immunity varies.

This variability in immunity can lead to severe respiratory signs when cattle are exposed to a heavy larval challenge, irrespective of the age of cattle. It is this reinfection syndrome that is responsible for coughing in adult dairy cows commonly referred to as ‘coughing cows’.

Early signs are often subtle — a light cough when animals are moved or exercised. But this can quickly develop into more noticeable symptoms such as persistent coughing, laboured breathing, drop in appetite, and reduced growth or milk yield.

Veterinary diagnosis usually involves lung washes or dung samples, but in acute outbreaks, vets may also make a diagnosis based on clinical signs and farm history. Where animals are severely affected, post-mortem examination can confirm the presence of adult worms in the lungs.

All classes of wormer are indicated for treatment of lungworm. These products can eliminate the parasite rapidly, but the sudden death of large numbers of adult worms in the lungs can cause a significant inflammatory response. In some cases, this reaction can make the animal’s condition worse before it improves.

For that reason, animals showing severe respiratory signs should be closely monitored following treatment. Additional supportive therapies, such as non-steroidal anti-inflammatories or antibiotics, may be needed to control secondary infections or inflammation. 

Severely affected cattle may also benefit from being housed or moved to a less contaminated pasture to reduce further exposure.

For more information, visit  www.norbrook.com