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Black scour worms

(Trichostrongylus colubriformis and Trichostrongylus vitrinus)

Black scour worms occur in all sheep production districts of Australia. Trichostrongylus colubriformis and Trichostrongylus vitrinus are the main species causing disease in Australia. Generally, T. colubriformis occurs in the warmer summer rainfall areas and T. vitrinus  occurs more frequently in winter rainfall areas.

T. vitrinus is considerably more pathogenic than T. colubriformis, meaning that it needs to be treated at lower egg counts. Regular worm egg counts are essential for successful management.

Adult female black scour worms lay 100–200 eggs per day. Black scour worms live in the first three metres of the small intestine of the sheep and cause damage to the lining of the gut. The adult female in the small intestine lays eggs, which are passed out in the dung.

Further ecological information on worms and their control:


Image: Black scour worm (Source: Professor Nick Sangster, University of Sydney)
Image: Black scour worm (Source: Professor Nick Sangster, University of Sydney)

Location

Small intestine (first 3 metres)


Signs

Death, lethargy and collapse, weight loss, damage and inflammation of the gut resulting in diarrhoea (scouring), hypersensitivity of the gut resulting in diarrhoea (scouring).


Image: (Left) Normal surface of the small intestine (Right) The wall of the small intestine damaged by black scour worm (Source: Dr Ian Beveridge, University of Melbourne)
Image: (Left) Normal surface of the small intestine (Right) The wall of the small intestine damaged by black scour worm (Source: Dr Ian Beveridge, University of Melbourne)

Diagnosis

The only accurate way to diagnose worm infections before productivity losses have occurred is to conduct a WormTest (worm egg count). The results allow you to make the best choice of drench for the situation.

Visual signs only occur after significant production loss has already occurred. Also, these signs can occur with other parasites and diseases.


Treatment

There are many options to treat sheep for this worm and your choice will depend on:

  • the current burden of this worm
  • what other worms are also present and in what proportion
  • the drench-resistance status and which drenches are effective on your property
  • the likely worm-risk over the next few months and the length of protection you are seeking
  • the likely level of worm contamination on your pastures
  • the class of sheep and their susceptibility to worms
  • the last drench group/s you used on this (and other) mobs
  • the time until these sheep are sold/slaughtered and the withholding period and export slaughter interval of drenches you might use

Your decision can be assisted by using the Drench Decision Guide, a simple tool that considers some of the points above.

You can also review the Drench pages on this site to find out specific information about drenches, including their drench active, drench group, length of protection, which worms they treat, dose rate, withholding period, export slaughter interval and manufacturer.

The negative impact of this worm can also be reduced through grazing management strategies and by using one of the integrated worm control programs, which have been developed for different regions across Australia.