With the mild winter we have been experiencing, we have seen some outbreaks of lungworm (Dictyocaulus Viviparous) in cattle, with mobs of young calves seriously affected.
A fungus, Pilobolus klenii has an important role in spreading the larvae over pasture. The fungal spores are eaten and germinate in the faeces. Then the lungworm larvae attaches to the fungal sporangium (bag of fungal spores). The sporangium fills with water and bursts, spreading spores and the attached larvae up to three meters infecting the surrounding area and in turn the stock grazing there.
A sudden exposure to a larval challenge in this situation can overwhelm the immune response and cause clinical signs in the stock ingesting them. In contrast to our usual gastrointestinal parasites, only a few hundred worms are required to produce clinical disease. The lifecycle of the worm starts with infection through the gut, larvae then migrating through the lymphatic system into the blood stream and then finally populating the lungs. Adults then develop in the lungs and cause bronchitis and pneumonia. Eggs are coughed up and swallowed passing through the gut to the pasture and the cycle begins again.
Clinical signs range from a mild cough and nasal discharge through to severe respiratory distress, coughing and death. Animals tend to continue to eat but may have the poor coat and condition seen with gastrointestinal parasitism.
Diagnosis is by finding larvae in the faeces but clinical signs and post-mortem are also useful indicators.
Treatment is by drenching with anthelmintics. We have not had any reports of resistance to drench classes and our modern drenches are effective against the immature and adult stages.
However, after treatment worsening of clinical signs may happen in heavily infested cattle as the dead parasites may accumulate in the airways. Severe cases may need anti-inflammatories to reduce the reaction to the larvae and antibiotics to treat secondary infections.
Give us a call if you are concerned about coughing calves, we are always on hand for advice.
