Interview with a vet: Lungworm poised to strike grazing cattle

Why is there cause for concern for autumn outbreaks of disease?

Insufficient immunity is increasing cases of lungworm in cattle, and this season is providing the perfect conditions for autumn outbreaks of disease, according to vet Claire Whittle.

 

What is lungworm disease?

Lungworm disease, also known as husk or hoose, is a serious respiratory disease which results in long-term losses in cattle productivity.

In young calves, growth rates can be reduced by over 20%1 and the cost of losses in production due to poor growth can average £50 - £100 per head2. In adult dairy cows, milk yield can be reduced, impacting herd profitability by around £3 per cow per day2.

Cattle which either fail to develop immunity to lungworm as young animals, or which do not receive an annual immunity boost as adults, are at high risk of developing disease.

 

Why do farmers need to act fast to control lungworm disease?

According to Claire Whittle, veterinary surgeon at LLM Farm Vets, this year is developing into a prime candidate for high levels of lungworm disease in the late summer and autumn, and she is urging farmers to prepare to act fast to control disease outbreaks.

“We are seeing changes in the seasonality of lungworm disease, with outbreaks coming earlier, and later, in the grazing season than we used to expect. Typically, these can now occur from July onwards, but last year was particularly bad and we even had a case in May,” says Claire, who covers livestock farms in Shropshire and surrounding areas.

Lungworm infectivity is driven by the weather, with warm and wet conditions increasing the likelihood for infection. The timing of turnout in the spring, and the climatic conditions during the grazing season, have an impact on the ability of lungworm larvae to reproduce and infect cattle.

Lungworm larvae on pasture do not survive for long when it is hot and dry. This year the conditions since turnout have kept worm challenge levels low. However, this means that adult cattle have not received an annual boost to their existing immunity, and calves and youngstock are not receiving any early-season challenge to help them build immunity,” says Claire.

“When the weather breaks and we get rainfall, larvae that are locked up in dungpats will be released and rapidly infect the pasture. With potentially low levels of immunity in cattle this year we expect to see significant disease outbreaks in late summer and early autumn.”

 

What management practices can farmers take to control lungworm disease?

A fine balance needs to be struck between allowing cattle some exposure to lungworm at grass, to build or boost immunity, while preventing high challenge situations which will result in disease.

“Vaccination before turnout provides rapid-onset immunity. It is a good option, especially for young cattle during their first year at grass, and for all cattle on farms with a known lungworm population,” explains Claire.

Alternatively, allowing cattle to receive a low dose challenge during each grazing season allows them to build long-lasting immunity to lungworm. However, this needs careful management to ensure increasing challenge doesn’t result in clinical disease.

“Assess the risk to groups of animals based on their grazing history and any worm treatments given over the past and current season,” advises Claire.

“If cattle have not had sufficient exposure to lungworm over the early grazing period the risk of disease will remain high, potentially until housing time in areas with milder weather.”

What about loss of lungworm immunity?

She warns that loss of immunity could be a particular problem this year:

“The unpredictable nature of lungworm means that sudden high challenge late in the year can overwhelm any immunity gained early in the season, even from vaccination.

“Weaned suckler calves and dairy heifers require particular attention, since even if they acquired some immunity at grass the previous season, this wanes during housing. They are effectively naïve again at turnout, and this year’s dry spring with limited exposure will compound the problem.”

 

How is lungworm diagnosed?

Lungworm is usually diagnosed by clinical signs.

“We usually err on the side of caution with lungworm,” says Claire. “Diagnostic testing to identify larvae, rather than eggs, in dung can be useful, but we mainly rely on animal history and observed symptoms to determine infection.”

Cattle with a lungworm infection will typically have a deep, harsh cough, most noticeable when they are moving, and their breathing may be laboured. As the lungworm burden increases, individuals may cough at rest and in severe cases cattle may salivate excessively and adopt an ‘air hunger’ position with head and neck extended, and their tongue stuck out each time they cough.

Increased resting, reduced grazing, weight loss and sudden milk drop may also be seen, especially in adult or lactating cattle.

Up to 10% of animals may be sub-clinical carriers of lungworm3, which means they may not show signs of disease but they will carry adult lungworms and contribute low numbers of lungworm larvae to the pasture. In effect, they are the silent spreaders of disease.

 

How to treat lungworm disease?

“Treatment is usually given to the whole group to ensure animals with infection but not yet showing clinical signs are treated and don’t become carriers. In severe cases, individual animals may require anti-inflammatory pain relief and additional supportive treatment.

“Secondary bacterial infections may also be present due to the lung damage inflicted by the worms, and in these cases antibiotic treatments may be required,” explains Claire.

 

Does lungworm cause lasting damage?

Unfortunately, once cattle have experienced lung damage from a lungworm infection, the impact is long-lasting and the animal will never be as productive as those that were unaffected. Financial losses will likely be hidden in slower growth, later bulling, and lower milk yields.

Lung damage can make cattle more prone to respiratory infections later in life, long after the lungworm has been treated. High stress events such as calving can prompt the return of pneumonia symptoms which will further reduce that cow’s productive potential.

“Prevention is the key,” says Claire. “Vaccination and a risk-based approach to worming at grass can help protect cattle from disease, while allowing them the opportunity to gain long-lasting, effective immunity.”

Although widespread, lungworm is not yet present on every farm.  Farmers should avoid importing it wherever possible, by quarantining and treating bought-in cattle. This will prevent exposing the home herd, which may be completely naïve to lungworm, and reduce the likelihood of a severe outbreak.

References

  1. COWS (2017) Make lungworm control a priority this spring [online] Available at: https://www.cattleparasites.org.uk/app/uploads/2018/04/Make-lungworm-control-a-priority-this-spring.pdf [Accessed 29 May 2020]
  2. COWS (2020) Control of lungworm in cattle [online] Available at: https://www.cattleparasites.org.uk/app/uploads/2020/01/lungworm-231219.pdf [Accessed 29 May 2020].
  3. Eysker M, Classens EW, Lam TGM, Moons MJ, Pijpers A (1994) The prevalence of patent lungworm infection in herds of dairy cows in the Netherlands. Veterinary Parasitology 53 (3-4) 263-267

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