Be vigilant of lungworm

After a sustained dry period, recent rainfall may have created the perfect conditions for lungworm to develop.

One of the most important respiratory diseases of cattle in Ireland and caused by Dictyocaulus viviparous, humid conditions following rainfall create the perfect conditions for lungworm to multiply.

With most of May and early June being dry, many animals will have experienced low levels of worm burdens thus far. However, with the conditions now right for lungworm populations to multiply, vigilance is key.

Lungworm lifecycle

The lungworm lifecycle can be broken down into a number of distinct phases. Adult lungworms live in the lungs and lay eggs, which are coughed up and swallowed. Older animals (yearlings and adults) may serve as carriers over winter, as some adult worms will survive in the lungs (either as fully mature or hibernating immature adults).

These eggs hatch and develop into stage one larvae as they pass through the intestine, before being released by the animal in their dung. In the dung pat, these stage one larvae develop into stage three larvae (infective larvae). Their progression from the base of the sward / dung pat is aided by the fungus Pilobolus or by rainfall. The splashing effect of water droplets helps to provide an avenue for these stage three larvae to move up the grass plant, at which point they are ingested by the animal.

Once ingested, these larvae pass from the intestine to the lungs and grow into adult worms. During this process, the larvae pierce the intestinal wall and move into the blood and lymphatic system to get to the lungs.

It takes 24-28 days from the day larvae have been eaten to the passing of eggs. If the weather is warm (approx. 20⁰ C) and humid, infective larvae may be available on pasture within seven days or less of being passed in the faeces.

Symptoms of lungworm

Symptoms of lungworm are usually seen in young cattle in their first grazing season in the later part of the summer. The nature and severity of lungworm infections depend on the number of larvae that are ingested and on the immune response of the animal.

Symptoms include:

• Mildly-affected animals will have an intermittent cough, especially after exercise.
• Moderately-affected animals will cough frequently at rest and have an increased respiratory rate.
• Severely-affected animals will have difficulty breathing and may adopt a mouth-breathing stance, with the head and neck out-stretched, mouth open and the tongue protruding.
• Lung damage can be severe and some of the pathology is irreversible, so deterioration of clinical cases and mortality can occur despite successful removal of the worms with an anthelmintic.
• Adult cows may also have a severe drop in milk yield. This can be observed before coughing is seen.
• Affected cattle have an increased susceptibility to other respiratory pathogens such as viruses and bacteria.

Treatment

Once a lungworm infection has been identified, treatment with one of the three classes of anthelmintic (white, yellow, clear) is required, with all three being effective against lungworm. Treatment of the whole group should be undertaken as soon as possible after the appearance of clinical signs in order to limit the impact of the infection. If treatment is delayed, lung damage may become advanced and irreversible. Where heavy infestations of lungworm are suspected, veterinary advice should be sought prior to treatment.

Animal Health Ireland has created a leaflet on ‘Lungworm – The Facts’, which is available here.