The large roundworm (Ascaris suum) is found in the small intestine of pigs and can grow to 400 mm long and 7 mm thick at maturity. Heavily infested pigs may have up to 250 worms blocking the small intestines and bile duct causing loss of appetite, vomiting and death. In less extreme cases there is reduced appetite, poor feed efficiency and slow growth. Pigs 6 to 12 weeks old are the most seriously affected, while mature pigs may carry the worms without ill effect. Growth rate and feed efficiency can be depressed by up to 10%.
The female roundworm is estimated to produce more than 300,000 eggs per day, which are passed in the dung of infected pigs. The eggs can survive for years in moist conditions to infect other pigs.
Larvae (immature forms) reach the liver after hatching from eggs in the small intestine and passing through the gut wall. Liver damage is seen as white ‘milk’ spots on the surface of the organ. Entering the bloodstream, larvae reach the heart and then the lungs where they may cause a low-grade pneumonia. After being coughed up and swallowed they mature in the small intestine.
The cycle from egg-to-egg production is completed within 2 months. The parasite is confirmed in a herd by the presence of eggs in the faeces and evidence of liver damage (milk spot) at slaughter.
The large roundworm is the most common and the most economically important internal parasite of pigs in Queensland. Improved control methods have reduced its effect – now only approximately 3% of pigs slaughtered in Australia show signs of having been affected by this parasite (as indicated by the Pig Health Monitoring Scheme).
The adult kidney worm (Stephanurus dentatus) grows to 50 mm and is located in fibrous cysts in the pig’s kidneys, uterus, flare fat, loin muscles and sometimes the spinal cord. As well as the adult worms the cysts contain a greenish pus. The immature or larval form is often found in the liver.
The migrating larvae damage the liver. Where the damage is severe affected pigs stop growing, build up fluid in the body cavity and may die of liver failure. When cysts develop in their spinal cord, adult animals may show paralysis of the hindquarters. Female worms in cysts with openings into the ureters and the kidneys can shed up to 1.5 million eggs in every urination. Blood is often passed in the urine.
Eggs hatch and after two moults the infective third stage larvae is reached in about 4 days. Both eggs and larvae are destroyed by sunny dry conditions or by extreme cold. Larvae can survive 3 to 5 months in warm moist soil sheltered from sunlight. If ingested by earthworms, larvae remain infective for long periods even under adverse soil conditions.
The pig is invaded by infective larvae via the skin or the stomach wall after ingestion. After moulting in the stomach wall or the skin, they reach the liver where they move around in the tissue for 3 months or more causing considerable damage. They then migrate principally to the kidney and surrounding tissues where females lay eggs about 6 months after infestation.
Some larvae, following an erratic migration path, reach maturity in the pancreas, spleen, brain, spinal cord and other organs. Unborn piglets can be infected in this way.
Infestations occur mainly in pigs kept in paddocks or earth-floored pens which have not been regularly and systematically spelled.
Improvements in piggery sanitation have diminished the importance of the kidney worm in Queensland. Diagnosis is made at post-mortem by examining the kidneys. Eggs will be found in the urine.
The zipper tapeworm, (Spirometra erinacei) is significant because the second larval stage causes sparganosis in humans. Humans risk contracting the disease if they eat feral pork infected with the immature form of the parasite.
The immature stage (spargana) are small white structures 8 to 15 mm in diameter resembling pieces of fat and are found on the lining of the body cavity, the diaphragm and on the heart and lungs. The affected pigs are condemned at slaughter, being unfit for human consumption.
The life cycle is complex and not fully understood. Adult tapeworms are found in dogs, cats, foxes and dingoes; the life cycle involves a water flea and other intermediate hosts. The spargana may be found in tadpoles, frogs, snakes, pigs and humans. In some areas of Queensland the parasite is found in feral pigs.
The whipworm (Trichuris suis and T. trichuria) is found in the pig’s large intestine.
The name comes from the resemblance to a whip, the long forward part being threadlike, the shorter rear portion much thicker. An adult measures between 30 and 50 mm. The worm can cause severe disease involving bloody diarrhoea and shedding of mucus. Affected pigs lose weight (up to 20%) and there can be a 10 to 12% death rate about 3 weeks after weaning. Swine dysentery symptoms are similar and the parasite may be implicated in the development of this disease. Whipworm infection should always be considered when there is diarrhoea with blood and mucus.
The life cycle is direct: the ingested eggs hatch and the larvae reach the lower gut without migrating through other organs. The eggs do not pass through any other host before becoming infective. In Queensland the disease is mostly seen in heavily stocked extensive piggeries. Eggs can remain viable for many years outside the pig and are easily identified in pig faeces.
Two species may infest pigs, of which Oesophagostomum dentatum is the more common. The larval stage produces nodules in the lower small intestine and the large intestine. The adult is greyish in colour measuring up to 25 mm.
Nodule worm infestation can cause slight diarrhoea and can reduce growth rate. The damage leaves the intestines unsuitable for use as sausage casings.
After being passed in the dung, eggs hatch and larvae reach the infective stage in a few days. When swallowed by the pig the larva sheds its protective sheath and burrows into the gut wall, causing a nodule. It grows to maturity in the intestine after a period spent in the nodule. It is not an important parasite of pigs in Queensland. Diagnosis is by identification of eggs in faeces.
The worms (Strongyloides ransomi and others) are about 4 mm long and are found in the upper part of the pig’s small intestine. They can cause enteritis, severe diarrhoea (often bloodstained), anaemia, poor growth and death. Piglets up to 8 weeks of age are most susceptible and death rates up to 75% have been reported.
Larvae penetrate the skin or are taken in through the mouth. Suckling pigs can be infected by larvae in colostrum. Dry conditions are hostile to larvae survival. The parasite is uncommon in Queensland. Diagnosis is achieved by identifying eggs in fresh faeces.
Red stomach worm.
This reddish-coloured worm (Hyostrongylus rubidus) is about 10 mm long and burrows into the pig’s stomach lining.
The worms cause the stomach lining to bleed; digested blood may be seen in the dung and stomach ulcers can develop. Affected pigs lose condition, have a ravenous appetite, become very thin and may die. Adult pigs can die following a sudden blood loss when ulcers perforate.
The parasite is thought to be involved in ill-thrift and the ‘thin-sow syndrome’. It is uncommon in growing pigs. The life cycle is direct; pigs are infected when eggs are taken in from contaminated pasture or soil. The red stomach worm is not common in Queensland. Diagnosis is by identifying worm eggs in the faeces and/or by post-mortem.
Three are known, Metastrongylus apri, M. pudendotectus and M. salmi. These are long white threadlike worms up to 50 mm long and can be found in the trachea and bronchial tubes of affected pigs.
Light infestations have little effect but heavier concentrations in young pigs may cause pneumonia and loss of condition.
Eggs containing active embryos are passed in the dung. The larva hatches but must complete its development after being swallowed by an earthworm. The pig is infected by eating the earthworm. Infestations are rare in Queensland. Diagnosis can be difficult as eggs are not easy
to find in faeces. Post-mortem is a more reliable method.
The thorn-headed worm (Macracanthorhynchus hirudinaceous) is whitish in colour, the females grow to between 180 and 400 mm long. The parasite firmly attaches itself to the small intestine wall with a thornlike part on its head.
Although infestations are uncommon in Queensland, the worm can cause severe damage as it moves and re-attaches itself to different parts of the gut wall. Occasionally the intestines are holed, resulting in peritonitis and death of the host pig. Eggs passed in the dung hatch in beetle grubs which are eventually eaten by the pig. The worms develop while attached to the intestinal wall.
Other worm parasites.
Large stomach worms (Ascarops strongylina and Physiocephalus sexalatus) have similar life histories involving beetles as intermediate hosts.
Both are stout pinkish worms up to 20 mm long and develop near the exit end of the stomach. Dung beetles are the intermediate hosts. The worms must be present in large numbers to cause problems.
Rare instances of sheep liver fluke (Fasciola hepatica) have been reported in the livers of pigs.
While pigs are not known to carry adult tapeworms, three types of ‘bladder worm’ or tapeworm cysts can infect pigs. Cysticercus cellulosae (pork measles) is the immature stage of the human tapeworm Taenia solium. The thin-necked bladder worm, Cysticercus tenuicollis is the intermediate stage of Taenia hydatigena, a tapeworm of dogs. The third type is the hydatid cyst, the immature form of a small tapeworm of dogs, Echinococcus granulosus.
The larvae of Trichinella spiralis causes trichinosis, a public health problem in many parts of the world; it is not found in Australia. It can infest pigs, rats, mice, dogs, cats and other mammals including people. Swill feeding (banned in Australia) helps to spread infection.
Control and prevention.
In indoor systems where all-in all-out procedures are used, internal parasites will not build-up in sufficient levels to require routine treatment.
Sows housed in stalls that have no access to faeces are usually only at risk from large roundworm infection. Parasite control in indoor loosehoused sows is less predictable and depends on hygiene, drainage and regular removal of faeces. In outdoor herds, parasite control is more difficult to achieve through hygiene and spelling paddocks, and regular chemical treatment is often required. Chemical control is administered through a variety of methods – some are injectable, others may be given orally or in feed or water.
*Always check the label before use – follow the directions and withholding period instructions (time before animal can be slaughtered for human consumption).