AFBI issues Nematodirus warning – Spring 2014

The Agri-Food and Biosciences Institute (AFBI) Veterinary Sciences Division wishes to advise sheep farmers of the likely risk of Nematodirus worm infection in young lambs occurring at this time of year.

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.

Nematodirus eggs passed out by lambs in 2013 generally remained unhatched on the ground throughout the winter season. Given suitable conditions of moisture and temperature, they underwent mass hatching in the spring of 2014, resulting in a high risk of infection for lambs. Affected lambs develop profuse scour and can die rapidly.

Hatching of Nematodirus eggs has already commenced and current meteorological readings indicate that peak hatching took place during the last week of March and first week of April.

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 recommendation, 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.

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.

by Hillary Edgar, Jason Barley and Bob Hanna,
Disease Surveillance and Investigation Branch,
Veterinary Sciences Division

Notes to editors: 

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