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Dublin: 8 °C Thursday 4 June, 2020

Deadly worm disease in lambs is on the increase, farmers warned

It takes almost a year before the egg hatches releasing the infective larvae.

THE GOVERNMENT HAS warned farmers of a increase in a type of lamb disease that could prove fatal if not treated.

The Department of Agriculture has advised farmers of the higher risk of the disease at this time of year, outlining symptoms, treatment and prevention measures.

What is it?

image006 Figure 1. Faecal sample with Nematodirus eggs (N) among a couple of strongyle eggs (S) and coccidial oocysts (O). Source: Irish Farmers Association

The disease ‘nematodirosis’ is a severe disease in lambs six to twelve weeks of age, which become infected through eating large numbers of infective larvae in contaminated fields.

The life cycle of the worms is unusual compared to other roundworms as it takes almost a year before the egg hatches releasing the infective larvae.

When does it happen?

There is a mass hatching of larvae in spring when the soil temperature increases after a period of cold weather and disease typically occurs in April, May and June.

The peak hatching of the larvae is predicted to be the last week of March along the south coast of Ireland, and into the first week of April for most of the rest of the country.

Nationally soil temperatures are warmer than normal for this time of year meaning larval hatching could occur 1-2 weeks earlier than in previous years.


shutterstock_383874619 Source: Shutterstock/nathanmcc

Infection is characterised by profuse diarrhoea, dehydration and weight loss. Mortality can be high in untreated lambs.

After ingestion, the larvae invade the intestinal mucosa and, in some cases, death may occur even before clinical signs of diarrhoea are observed. Ewes are not affected.

Early lambing flocks and enterprises with higher stocking rates, where lambs are grazing pastures grazed by last year’s lambs, are particularly vulnerable.

Twin lambs may be at risk of developing disease earlier compared to their single lamb counterparts as they begin grazing greater amounts of grass earlier in life.

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How can it be treated?

Benzimidazoles, or white drenches, remain the treatment of choice and are effective against both larval and adult stages of this worm.

shutterstock_607813955 Source: Shutterstock/SandyKern

Along the south coast of the country, lambs should be dosed with a suitable anthelmintic by the second week of April (two weeks post peak larval hatching), while lambs in the rest of the country should be dosed from mid-April depending on farm location and individual flock factors.

This disease is best prevented by keeping the current year’s lambs off pasture that was grazed by lambs or young calves in the previous year.

Despite this, there are no drenches with effective residual activity against ‘nematodirus’ which means that as the lamb continues to graze, it can become re-infected with larvae again and as a result may need repeated treatments at two to three week intervals.

If lambs die unexpectedly, it’s advised they’re referred by your vet to a regional veterinary laboratory for postmortem examination as ‘nematodirus’ can be fatal before symptoms appear.

Read: ‘Farmers are at their wit’s end’: Losing your land, home and income at the hands of vulture funds

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