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Kidney worms (Stephanurus dentatus)

(497) This is an important parasite commonly found in North America.

The life cycle

The adult females form cysts in the kidney fat and pass eggs out into the urine which develop to infective larvae in 2-7 days.

The cycle can be a direct one through the intake of infected larvae by mouth or penetration through the skin, or indirectly through infected earth worms. The larvae migrate from the intestine throughout the body over a period of 4-6 months before they finally arrive at the kidneys to mature. The cycle from egg to adult is a long one (up to a year) and the females lay very large numbers of eggs each day.

Clinical signs

Stephanurus dentatus is found only in warm wet countries because the larva dies out very quickly in cold conditions. The larvae cause severe damage, particularly in the liver, as they migrate throughout the body and they cause loss of appetite and body condition. Blood is often passed out in the urine. There is considerable wasting of muscles.


This is made at post-mortem by examination of the kidneys and milk spot lesions will also be evident at slaughter. Eggs will be found in the urine.


  • See Fig.11-9. below
Management control and prevention
  • Prevent access to infected earth worms.
  • As the worm takes so long to develop to an adult it is important to maintain a young breeding herd.
  • Keep pens clean and well drained.
  • See introduction.

Fig 11-9 TO DO

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