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Large White Worms or Ascarids (Ascaris Suum)

(498) This is 250 to 400mm long and often seen in the faeces of sows and finishing pigs. Female worms are very prolific producing 0.5 to 1 million eggs per day and these will survive outside the pig for many years. They are resistant to drying and freezing but sunlight kills them in a few weeks. It is a common parasite found world-wide and probably the most important one economically.

The life cycle

This is direct. It takes 2-8 weeks for the larva to develop inside the egg and become infective. The eggs after ingestion hatch in the intestine, the larvae migrate through the wall and via the blood enter the liver. They then migrate through the liver to the lungs, finally reaching the trachea where they are coughed up, swallowed and returned to the small intestine to develop into adults. The cycle from egg to egg production is completed within two months.

Clinical signs

Large numbers of worms in the intestine absorb food and interfere with digestion. As the larvae migrate through the liver, liver damage (milk spot) results in condemnations at slaughter. The liver lesions heal in 5-6 weeks.

Heavy larval migration through the lungs causes coughing and pneumonia and may activate latent respiratory diseases. Both growth rate and feed efficiency may be depressed by up to 10%.


This is confirmed by the presence of eggs in the faeces and evidence of liver damage (milk spot) at slaughter.


  • See Fig.11-9. below
Management control and prevention
  • Contaminated pens are the most common source of infection hence the adoption of all-in all-out strategies is important in control.
  • See introduction.

Fig 11-9 TO DO

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