AFBI issues Nematodirus Warning – Spring 2024

Date published: 04 April 2024

Area of Expertise:

AFBI wishes to advise sheep farmers of the likely risk of Nematodirus worm infection in young lambs, currently occurring at this time of the year.

Nematodirus infection results from the ingestion of large numbers of infective worm larvae present on contaminated pasture

Nematodirus infection results from the ingestion of large numbers of infective worm larvae present on contaminated pasture. Lambs grazing the same pasture in the previous year were the source of this contamination. For Nematodirus eggs to hatch they should experience a period of cold weather followed by warmer conditions. These conditions are usually achieved during the winter and spring of each year. Nematodirus eggs passed out by lambs in 2023 will generally have remained unhatched on the ground throughout the winter season. Given suitable conditions of moisture and temperature, they will undergo mass hatching in the spring of 2024, resulting in a high risk of infection for lambs. Affected lambs develop profuse scour and can die rapidly.

Using a forecasting system based on climate data, staff at the Institute have determined that hatching of Nematodirus eggs has already commenced, and that 10% of the annual hatch would have occurred in mid-March 2024. The current meteorological readings indicate that peak hatching is taking place at present, in this first week of April 2024.

Nematodirus normally only affects lambs between 6 and 12 weeks of age and clinical signs usually appear two weeks after ingestion of large numbers of larvae. Although rare, Nematodirus infection can occasionally cause problems in young calves. Therefore, farmers should be on the alert for signs of scour in lambs (and possibly young calves at grass) from mid - April into May.

Farmers should be aware that Nematodirus infection might be confused with coccidiosis, another disease which can cause severe scour in young lambs. As the treatments for Nematodirus infection and coccidiosis are different, accurate diagnosis and treatment recommendations, through your veterinary surgeon, are essential.

Nematodirus disease can be avoided or reduced in lambs by:

  1. not grazing lambs on the same fields as those grazed by lambs of a similar age last year.
  2. using anthelmintic drenches every 2 to 4 weeks. The interval between doses depends both on the particular anthelmintic used and the severity of infection. To date, only limited evidence has been found of drug resistance in Nematodirus to any of the available classes of anthelmintic.

Eggs of Nematodirus (A), strongyle worm (B) and coccidian (C) in a faeces sample collected from a scouring lamb
Eggs of Nematodirus (A), strongyle worm (B) and coccidian (C) in a faeces sample collected from a scouring lamb
An added cause of concern for sheep farmers this year is the possibility that Haemonchus infection may be prevalent amongst growing lambs in the summer months. Last year, unprecedented localised increase in Haemonchus infection in sheep was noted, likely linked to the mild wet climatic conditions. As a result, pasture in affected areas is likely to be contaminated by parasite eggs surviving from last season, and yearling animals are likely to be carrying hypobiotic larvae, which will be a source of infection for growing stock later in the season. Haemonchus infection causes profound anaemia in lambs, often with scour which may be blood-stained. Animals succumb rapidly, and numerous losses can occur in affected flocks. 

Your veterinary surgeon should be consulted at an early stage. He or she is in an ideal position to provide advice on the prevention and /or treatment strategy best suited to your particular circumstances. AFBI’s Veterinary Sciences Division can test faeces samples from sheep or cattle to determine the level of worm eggs present. A minimum of 5 grams of faeces from each animal is required for this test. Any animals which die showing signs of bloody scour and/or anaemia should be submitted for post-mortem examination and testing for haemonchosis.

Notes to editors: 

AFBI’s Vision is “Scientific excellence delivering impactful and sustainable outcomes for society, economy and the natural environment”.

AFBI’s Purpose is “To deliver trusted, independent research, statutory and surveillance science and expert advice that addresses local and global challenges, informs government policy and industry decision making, and underpins a sustainable agri-food industry and the natural and marine environments”.

AFBI’s core areas:

  • Leading improvements in the agri-food industry to enhance its sustainability.
  • Protecting animal, plant and human health.
  • Enhancing the natural and marine environment.

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