Husk: Are you in control of lungworm?

Over the last 25 years, lungworm has been on the increase. This is a result of climate change and milder and wetter weather, extended grazing seasons and reliance on long-acting anthelmintics for lungworm control.

Although found across Great Britain, lungworm is most commonly seen in wetter, western areas. Outbreaks of lungworm are unpredictable, with more variation year-to-year, farm-to-farm and pasture-to-pasture than is seen with gut worms and liver fluke.

Although many herds are affected, many do not show signs of disease. However, when the circumstances are right, outbreaks can occur (see high risk conditions). While young cattle in their first grazing season are most at risk of disease, older cattle can be at risk too. It is, therefore, a good idea to review your lungworm prevention plan with your vet, SQP or RAMA regularly.

Cattle develop natural immunity to lungworm, which starts to develop 10 days after infection, but this immunity is short lived (four months to two years) – dependant on whether adult worms reach the lungs. Natural immunity is, therefore, lost unless there is ongoing exposure to lungworm larvae.

Asymptomatic carrier animals act as an important source of ongoing contamination for pasture in the spring. Even where cattle have previously been exposed and acquired some immunity, sudden and heavy lungworm larval levels caused by favourable weather conditions may lead to disease.

High-risk conditions for lungworm

• Wet summers
• Heavy stocking densities
• Lack of immunity due to low exposure to lungworm larvae

Clinical signs

Clinical signs of the disease are commonly seen in mid-summer (July) to autumn and include:

• Coughing in grazing cattle
• Rapid or difficulty breathing, particularly after exercise
• Extended head with tongue sticking out and frothy saliva
• Loss of condition
• Reduced milk yield in adult cows
• Death

Impact

Losses in severe lungworm outbreaks in growing cattle can average £50–£100 per head. Lost milk production in adult cattle may reach £3 per cow per day.

Prevention

On farms with no history of lungworm, the risk of introduction is through bought-in stock. Ensuring adequate quarantine measures are in place to reduce this risk is key. Discussing an appropriate quarantine programme with your vet will help to protect your herd from lungworm as well as other bought in disease.

For farms with a history of lungworm, the best method of prevention is to vaccinate at-risk cattle; the vaccine is orally administered and very effective. Vaccination before turnout allows cattle to develop short-term immunity until longer-lasting cover can develop naturally.

Wormers only provide temporary protection against lungworm (four to five months) and can leave cattle at risk towards the end of the grazing season. Overuse of wormers can also mean cattle fail to create their own immunity. Using wormers “as little as possible but as much as necessary” supports natural immunity, helps to slow the development of drug-resistant parasites, reduces unnecessary expenditure and helps protect biodiversity in the environment. The lungworm vaccine does not provide protection against gut worms and a risk assessment for other worms should also be carried out.

Prevention of lungworm through pasture management is not as easy as it is for gut roundworms, however, following an outbreak of clinical disease the pasture in question should be considered contaminated. At-risk animals should not graze contaminated pastures for the remainder of the season, nor the start of the subsequent season, unless they have been vaccinated.

Which cattle to consider vaccinating for lungworm

• Cattle in their first grazing season
• Unvaccinated cattle
• Purchased cattle with unknown vaccination status
• Cattle not exposed to normal lungworm levels in their last grazing season

Key messages

• Be aware of bought-in animals that could bring in infection or be immunologically naïve
• Appearance of lungworm is unpredictable, so low-risk grazing strategies are less reliable
• Cattle in their first grazing season are most susceptible to lungworm

When selecting the most appropriate products to use against lungworm, it is important to consider other worming requirements. Changes to strategic anthelmintic programmes for gastrointestinal nematode control may have an impact on lungworm control.

To avoid any unintended consequences, seek advice from your vet, RAMA or SQP.

Further information