Farm Ireland

Wednesday 25 April 2018

rumen fluke diseASE now a major animal health threat

Spotting and dealing with the condition is tricky for herd owners and vets writes Mícheál Casey

Micheal Casey

The rumen fluke (scientific name Paramphistomum cervi) was little known outside parasitology circles until recent years. It used to be considered harmless, and small numbers of these short pink maggot-like parasites are commonly observed in the first stomach (rumen) of healthy cattle and sheep at slaughter.

Much heavier burdens of adult rumen flukes have been observed in cattle and sheep from some Irish farms in recent years by the regional veterinary laboratories. This phenomenon has also been reported from Northern Ireland and south-western Britain.

Although adult flukes seem relatively harmless, a small number of outbreaks of severe rumen fluke disease have been seen on farms in the north-west, the south and the midlands, caused by very heavy burdens of immature (larval) flukes. This stage of the parasite feeds on the lining of the upper part of the small intestine (the duodenum) and causes very severe enteritis and diarrhoea if large numbers of larvae are present.

What are the signs that rumen fluke may be in your herd?

The clinical disease is rare, but tends to be very severe when it occurs. Affected animals are dull, dehydrated, and lose weight rapidly. They develop a profuse and severe watery scour, which may contain traces of blood. Affected animals may become anaemic, and if blood protein levels drop sufficiently, may develop a swelling under the jaw -- known as bottle-jaw.

How do I confirm that rumen fluke is causing these signs?

Confirming milder cases is not easy -- other parasites may cause similar signs. Your vet can advise on whether rumen fluke may be involved, and may take samples for testing.

Laboratory testing may detect rumen fluke eggs. But this merely proves that the animal is carrying adult rumen flukes (not uncommon). It is much more difficult to confirm disease caused by immature flukes, as there are no conclusive findings in faecal or blood samples. Your vet will interpret the results in light of the clinical signs shown by the animals.

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A post-mortem examination of animals that die after showing the signs described above is more reliable, especially if the carcass is examined immediately after death.

Why do only certain cattle or herds develop disease due to rumen flukes?

Cattle and sheep appear to be more susceptible to rumen fluke infestation if they are young, sick or poorly nourished. However, if there are very large numbers of infective larvae on the grass, all cattle and sheep are susceptible to some degree.

Why has there been a recent increase in reported cases?

We have had a lot of summer flooding in recent years, and several mild winters (until last year) and these may have favoured outbreaks. It is unclear whether the rumen fluke phenomenon is a temporary blip because of extreme weather, or the start of a trend.

How can I control rumen fluke in my herd?

  • Dosing with an effective product -- most flukicides are not effective against rumen flukes. Oxyclozanide is the only active ingredient on the Irish market which kills all stages of rumen flukes, though it is only licensed for liver fluke control. Oxyclozanide is marketed in a number of different formulations -- on its own or with a wormer. It is not very effective against immature liver flukes, but seems to kill immature rumen flukes quite satisfactorily.
  • Prevent introduction of rumen flukes onto your farm -- consider treating bought-in animals of unknown origin or animals that are from known fluke-infested farms with oxyclozanide before introducing them to your farm.
  • Prevent exposure to heavily infested pasture -- restrict access to areas that are prone to flooding. The fencing-off of drains, ponds and watercourses will help.

Why not just dose everything?

The detection of rumen fluke eggs in faecal samples or of the adults in small numbers in the rumen is not in itself a reason to dose animals, as light infestations appear to have no effect on health or productivity.

Routine preventive dosing for rumen fluke is rarely justified, except on farms where severe disease and losses have been confirmed in the past. Because of the rarity of such outbreaks, there is no justification for blanket dosing.

Apart from the economic costs that arise from unnecessary use of any anti-parasitic drug, excessive use risks the development of oxyclozanide-resistant strains of rumen fluke. Furthermore, oxyclozanide is known to cause some side effects in cattle, including transient scour after dosing.

There is a real risk that the growing awareness of rumen fluke could distract the focus from the far more common and harmful liver fluke, particularly in sheep, and especially if oxyclozanide is selected to cover both infestations.

Oxyclozanide, while suitable for treating confirmed cases of rumen fluke infestation, is not effective against immature liver fluke. Animals dosed with oxyclozanide may continue to carry significant burdens of immature liver flukes.

Animal Health Ireland is to launch a more detailed information leaflet on this emerging parasite in the next month summarising relevant knowledge for producers and advisors.

Mícheál Casey works for the Department of Agriculture's Regional Veterinary Laboratories

Irish Independent