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Flukes and worms

Course: Diseases and pests in cattle | Last Updates: 7th October 2015

Professor Mike Taylor
Vet consultant
Biography >>

Incidences of liver fluke and lungworm in cattle are increasing, and the farming industry needs to act now to prevent resistant strains of parasites from developing.

Experience in the sheep industry shows how over-reliance on anthelmintics can result in the development of new, resistant parasite strains. By learning from that, and adopting a more integrated control strategy, dairy and beef producers can reduce both the burden on their cattle and on their profits.

What are the most common parasites affecting cattle?

Ostertagia ostertagi, a roundworm also known as the brown stomach worm, is the main parasite associated with disease in calves. However, another roundworm species, Cooperia, is very common in young cattle in their first grazing season and is the main contributor to faecal worm egg counts.

Lungworm, or Dictyocaulus viviparus, is usually seen in first-year grazing animals in summer or early autumn and, over the past few years, has been increasingly reported in older animals. Parasitic bronchitis, caused by lungworm, is now recognised as the commonest respiratory disease of adult cattle in the UK.

Disease due to liver fluke is caused by the trematode parasite Fasciola hepatica. Over the past 10 years liver condemnations at abattoirs due to fluke have soared to about 20%, depending on region, with even traditionally drier regions of the country now beginning to be affected.

How does infection occur?

To control infection of cattle by parasites, it is essential to understand their life cycles.

The life cycles of the gastrointestinal nematodes are very similar. Eggs are passed in the faeces and, under optimal conditions, develop to the infective stage within two weeks. In moist conditions the larvae migrate from the faeces on to the grass and are ingested by grazing cattle. The larvae then develop into adult worms, over a period of about three weeks, which go on to lay more eggs in the intestines.

Lungworms develop slightly differently. The adult worms in the lungs produce eggs containing fully developed larvae that hatch almost immediately. These migrate up the trachea, are swallowed, and pass out in the faeces. Under optimal conditions infective larvae can develop within five days, and migrate onto the grass, before being ingested. They travel to the lungs via the lymph and blood, where they break out of the capillaries into the lung alveoli about a week after infection. After a few days they moult and move up the bronchi to mature.

The life cycle of the liver fluke parasite is more complex, involving an intermediate host, a mud snail, and several free-living stages. The role of the snail, which prefers muddy, slightly acidic conditions, means that the incidence of liver fluke is far greater in wetter areas of the country and in years when there is high summer rainfall.

Adult fluke lay eggs in the bile duct, which are passed out in the faeces. At suitable temperatures, a larva develops, hatches and actively seeks out a snail host. Within the snail it multiplies, and, with the snail’s capacity to produce 100,000 offspring in three to four months, there is potential for very large numbers of parasites on the pasture. Eventually the larvae emerge from the snail onto wet grass, where they encyst into a highly resilient infective stage.

Following ingestion the young fluke migrate to the liver, through which they tunnel, causing tissue damage, on their way to the bile ducts. The infection is evident about 10–12 weeks after ingestion, and the whole cycle takes 18-20 weeks.


What symptoms should you look out for?

All types of infection can result in poor weight gain and performance, and may precipitate increased rates of concurrent illness.

Roundworms typically affect young calves during their first grazing season, resulting in parasitic gastroenteritis, symptoms of which include diarrhoea and weight loss.

Lungworms act differently, although they, too, tend to affect young cattle during their first grazing season. Infection is characterised by bronchitis and pneumonia, and can range from a mild cough to rapid breathing and severe shortness of breath. Most animals recover slowly after treatment, but death can occur in some cases.

Liver fluke affects cattle in two stages – immature fluke migrating through the liver may cause liver damage and haemorrhage, while heavy infections of adult fluke in the bile ducts feed on blood, resulting in anaemia and sometimes "bottle" jaw, or oedema. Growth rates can drop by up to 20%, and milk yields may fall by up to 8%, with reduced fat quality.

What treatment is needed?

A wide range of cattle worming products is available in the UK, most of which are used for both treatment and prevention. They are available as injections, drenches, pour-ons or boluses. Broad-spectrum anthelmintics are effective against a range of parasites, while narrow spectrum wormers are more targeted against fluke and some bloodsucking nematodes.

However, different products act against different life stages of worms and fluke, and should be administered accordingly – wormers used at grass will be different from those required upon housing or through the winter. EBLEX has produced a leaflet detailing individual use and dose requirements for a wide range of wormers, but producers should develop a worming strategy in conjunction with their vet. Remember to rotate the type of wormer used to avoid resistance building up, and use products as directed based on accurate cattle bodyweights.

How can you prevent infection in the first place?

Following repeated exposure, cattle become immune to gastrointestinal nematodes and lungworm over one to two grazing seasons. However, producers facing a major lungworm problem should consider vaccinating, which can reduce the need for routine worming.

Often, producers rely too heavily on routine dosing, making the development of resistant parasite strains more likely. Instead, they should adopt a more strategic approach, including rotation of pasture and use of faecal egg counts, to better target wormers and cut costs.

As youngstock are most at risk of worms, try to graze them on low-risk pasture such as new leys or fields previously grazed by adult cattle or sheep. Use older cattle to clean up the larvae present in high-risk fields. Older cattle rarely need to be treated, as they will have built up immunity, and calves grazing low risk leys should also not need routine treatment.

Undertake regular faecal egg counts when planning to worm, to identify the need for it, and occasionally repeat afterwards to check the efficacy of the wormer used. Tests to identify the dominant parasite type can also be carried out, to ensure targeted treatment.

In the case of fluke, consider draining wet pastures to reduce the number of snail hosts. Warm and wet conditions create the ideal environment for fluke, and global warming may be contributing to its spread across the country. Try to eliminate poached land around water troughs and gateways and fence off marshy areas.


Golden rules

  • Reduce dependence on wormers by monitoring faecal egg counts
  • Prevent the introduction of resistant worms or fluke by quarantining and treating bought-in animals
  • Wherever possible work out a control strategy with your vet or adviser
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