AFBI issues Nematodirus warning for Northern Ireland

The Agri-Food and Biosciences Institute (AFBI) Veterinary Sciences Division has issued a warning over Nematodirus in Northern Ireland.

Nematodirus worm infection in young lambs is a seasonal risk to lambs; however, this year, the institute warns larvae are hatching earlier than normal. Affected lambs develop profuse scour and can die quickly.

A similar warning was issued for the Republic of Ireland earlier this month.


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 must experience a period of cold weather followed by warmer conditions. These conditions are usually achieved during the winter and spring of each year.

A spokesperson for the institute said: “Nematodirus eggs passed out by lambs in 2020 will generally have remained unhatched on the ground over the winter season. Given suitable conditions of moisture and temperature, eggs will undergo mass hatching in the spring of 2021, resulting in a high risk of infection for lambs.

“Using a forecasting system based on climate data, staff at the institute have predicted that hatching of Nematodirus eggs has commenced and current meteorological readings indicate that peak hatching will take place during the first and second week of April 2021.

“Nematodirus normally only affects lambs between six and 12 weeks of age and clinical signs usually appear two weeks after ingestion of large numbers of larvae. Affected lambs develop profuse scour and can die rapidly.

“Although rare, Nematodirus infection can also 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.”

Don’t confuse with cocci

However, farmers should be aware that Nematodirus infection can be confused with coccidiosis, which also causes severe scour in young lambs.

As the treatments for Nematodirus infection and coccidiosis are different, accurate diagnosis and treatment are essential.

Check out Agriland this Saturday for sheep specialist Michael Geary’s advice on how to differentiate between the two diseases.

AFBI’s Veterinary Sciences Division can also test faeces samples from sheep or cattle to determine the level of worm eggs present. A minimum of 5g of faeces from each animal is required for this test.

Nematodirus disease can be avoided or reduced in lambs by:

  • Not grazing lambs on the same fields as those grazed by lambs of a similar age last year.
  • Using anthelmintic drenches every two to four 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.

AFBI advises farmers should consult their veterinary surgeon at an early stage.

“He or she is in an ideal position to provide advice on the prevention or treatment strategy best suited to your particular circumstances,” the AFBI spokesperson added.