Pig Parasites

External Parasites
Mange	The mange mite Dirty ears in an adult boar
Mange is caused by infection with the microscopic burrowing mite Sarcoptes scabiei var suis. All parts of the its life cycle, the egg, larvae, nymph and adult develop below the surface of the skin and only require 15 days to complete. Experimentally the mite can live for up to 3 weeks off the pig, however, at temperatures higher than 25C the mite does not survive more than 3 days. The consistent clinical sign is rubbing and scratching. All ages can be affected from weaner to adult and the worse cases can be in the growing pig with PRRS infections. Classical signs are excess wax in the ear form which the mites can be identified, however, it can take 25 scrapes, even from infected herds, to find the mite. Monitoring of mange is carried out in the slaughterhouse. Treatment and control is by the establishment of mange free herds or in chronically infected herds by the use of in-feed or injection of ivermectins or pour on pesticides. It is estimated that about 70% of the UK national finishing herd is infested with mange. Up to 10% loss in FCR and growth rates have been reported. The mite is not infective to man.
Lice
The pig biting louse is Haematopinus suis. These are the biggest louse known to man and are readily observed. The life cycle occurs on the body and takes 30 days to complete from egg to adult, however, the louse cannot live for more than 3 days away from the pig making control technically easier than with mange although in practice this has proven more difficult. It is possible that swine pox may be carried by lice. Lice are very sensitive to standard mange treatments.
Internal Parasites		Egg Worm from anus White spots on the liver surface
Ascaris –milk spot
Ascaris suum is a large round worm which lives in the intestinal tract of pigs, with a prevalence of between 50 and 75% of herds. The female worm produces around 2 million eggs per day, however, production is very variable. The eggs are difficult to find in the faeces and special techniques are employed to attempt to find the egg. The eggs are very sticky and are resistant to most disinfectants, but heat (steam) are direct sunlight are effective in destroying the egg’s viability. The eggs are able to survive for more than 7 years in pasture or housing. Once ingested the egg hatches and the larvae pass through the intestinal wall and migrate via the blood stream to the liver. The worm is only in the liver for 5 days. The liver damage heals by scarring, producing the white marks on the liver surface or ‘milk spot liver’. These lesions heal within 25 days. The larvae leave the liver and migrate to the lungs where they contribute to respiratory diseases such as Enzootic pneumonia or Swine Influenza. Ascaris may cause a cough in piglets in the farrowing house. The larvae are then coughed up and swallowed and once back in the intestinal tract they mature to adults. The time interval from ingestion to producing eggs can be as short as 40 days. Ascaris is important to the pig industry as the disease reduces growth rates and feed conversion and may aggravate other diseases. It also has a direct economic loss to the slaughtering industry though liver condemnations.

Strongyle worms
There are two important strongyle worms in the pig. Hyostrongylus rubidus, the red stomach worm and Oesophagostomum dentatum which lives in the large intestine. Neither of these worms migrate around the body, but live in the wall and lumen of the intestines causing local damage which results in poor food conversion and growth. They both contribute to the ‘thin sow syndrome’ and while controlled in housed sows may become an increasing problem again with loose housing. The level of infestation is calculated through the worm egg count.
Whip worms
Trichuris suis is the pig whip worm and lives in the large bowel and causes local damage to the intestinal wall. These worms do not migrate around the body. This may play a marginal role in the ‘thin sow syndrome’. They are readily recognized through a worm egg examination through their bipolar egg shape.
Trichinella spiralis
This is an important parasite of the pig, but is rare in the undeveloped countries. The worm is important as man may become infected resulting is severe muscular pains and swelling of the face. The life cycle is different from the worms described so far. The adult worm lives in the intestine of pigs, but no eggs are laid. The larvae develop within the female worm. The larvae are released from the female and migrate through the intestinal wall moving through the body eventually localizing in muscle tissues. Here they wait (for up to 24 years) until the muscle in eaten by another pig, a rat or man, when the live cycle starts again. Diagnosis of trichinella is through examination of muscle tissues, especially the diaphragm.
Lung Worm
The pig lung worm is called Metastrongylus apri. This adult worm lives in the bronchi and bronchioles of the pig where it can cause local damage and coughing. The eggs containing fully formed larvae are laid by the female, coughed up, swallowed and passed out of the pig via the faeces. The larvae is then eaten by an earthworm where it remains in the blood vessels. The earthworm is eaten by the pig and the larvae migrate through the intestinal wall to the lungs where the cycle starts again. Earthworms are able to live up to 7 years and so once pasture is infected it will take a long time to eliminate the parasite.
Other round worm parasites
There are a number of other parasites especially in the warmer climates, two worthy of note are Stephanurus dentatus (the kidney worm), very common in the southern states of the USA where the migrating larvae can cause severe liver damage and Strongyloides ransomi which is a worm which can kill piglets due to diarrhoea resulting from damage to their intestinal tract. Photo shows liver damage with Stephanurus dentatus
Tape worms
With increased vigilance in the slaughterhouse, tape worms of pigs are now rare. Of particular important is Taenia solium, where the pig and man is the intermediate host. The larvae develop into a cyst and when infected pork is eaten by man the tape worm develops in the intestinal tract.

The routine examination for the presence of intestinal parasites is through the “worm egg count” details can be found here

Pig Parasites General

The major sites where the parasites of the pig can be found