Article written by Molly Morrison MRCVS
Lung worm is caused by the parasitic nematode Dictyocaulus viviparus in cattle. Clinical disease is most commonly in late summer to autumn, when larval burdens on the pasture are highest. In 2025, we saw an explosion of lungworm cases after the late august rain.
It has a direct life cycle, with infective third-stage larvae being ingested from pasture. Each larvae is programmed to migrate from the gut to the lungs, where they mature into adults. It is an amazing lifecycle!
Who is at risk?
Cattle of any age or breed who have not built-up immunity through natural exposure or vaccination are at risk, including:
Suspect a case of lung worm?
Once you have had a case of lungworm, the clinical signs are very easy to spot. Clinical signs are caused by irritation and airway obstruction of the bronchi by adult lungworm and the migration of lungworm larvae through the lung tissues. If you suspect you have cases of lungworm on farm call your vet who can help confirm diagnosis and treat clinical signs!
Cost on farm
Infections result in reduced growth rates and future productivity due to permanent lung damage. Studies estimate economic cost per adult diary cow to be £140 and £50-100 per beef cow. These figures relate to the cost of treatment and veterinary care, loss of body condition, decreased fertility and loss of milk production which is estimated to be 4kg/cow/day in dairy cattle.
How to create immunity
Cattle can develop natural immunity to lungworm, it will start to develop within 10 days post infection. However, having developed this immunity, cattle need to continually ‘top-up’ their immunity. If they fail to do this, lungworm larvae immunity can be lost in as little as six months and clinical signs seen again.
In times of drought, this lack of top-up exposure is particularly common as the larvae burrow below ground or dessicate. In 2025 we saw freshly calved autumn calvers develop lungworm, having been turned out onto clean grazing during drought conditions. Continuous but controlled exposure is therefore necessary for immunity to be sustained.
Vaccination a suitable solution?
Vaccination before turnout is an effective and reliable method of protecting a herd against lungworm. Continual exposure once vaccinated is essential to maximise the immunity generated from Huskvac and develop immunity to the adult stages. Careful grazing management is required when you invest in Huskvac.
The vaccine, Bovilis® Huskvac (MSD Animal Health) contains live irradiated lungworm larvae that stimulates type 1 immunity. To ensure longer term protection, cattle need to be turned out onto low level infective pasture which allows a natural boost to their immunity. If you are a new or current user of Huskvac, please do contact your vet to discuss your grazing management and ensure that we maximise immune development post-vaccination. The vaccine is now available and will remain so until August.
