The most important worm here is Hyostrongylus rubidus. Its life-cycle is direct. (See also THIN SOW SYNDROME.) The latter may sometimes be due to various species of Oesophagostomum worms. (See OESOPHAGOSTOMIASIS.)
2. Small intestine
Ascaris suum. This worm is a very common parasite of pigs in all countries.
The eggs have a remarkable vitality, and have been kept alive for as long as 5 years. The egg, in a few weeks after passing to the ground, develops an embryo, but this does not hatch until the egg is swallowed. When this happens, the larva, which is about 0.25 mm long, bores through the intestine, reaches the bloodstream, and is carried through the liver and heart to the lungs. Here it remains for some days, but it finally climbs up the trachea and is swallowed. The larva which leaves the lung has grown to about 2.5 mm in length. In the intestine it continues its development, taking about DA months to do so.
In passing through the lungs a certain amount of bleeding is caused, and if the larvae are numerous, pneumonia results. During this period the animal shows the symptoms known as ‘thumps’. If it survives the lung symptoms, it often fails to grow properly and remains small and stunted.
Macrocantorhynchus hirudinaceus is found in the small intestine of pigs. It is a whitish worm, the male being 5 to 10 cm long, while the female is 20 to 35 cm long. The neck is thin and the posterior region stout. The intermediate stages are found in beetles.
The parasite may cause a catarrhal enteritis or even actual perforation with peritonitis.
Trichuris suis, the pig whip-worm, causes mainly subclinical disease in temperate climates, but in the tropics it may cause dysentery, anaemia, and even death. In the Americas up to 85 per cent of pigs may be infested; in some areas of the UK, from 75 per cent. Trichuris occurs in the caecum.
Treatment in the pig includes oxibendazole, fenbendzole and thiophanate.
In pigs 2 species are common, both belonging to the genus Metastrongylus. The male is about 2 cm and the female about 4 cm long. Both species are common in Europe and America, and may occur in the same pig. They cause a verminous bronchitis and sometimes pneumonia. Young animals are more susceptible and may die from it. Both species are carried by earthworms.
Trichinella spiralis. This is a small worm found in the intestine. The female produces living larvae (0.1 to 0.16 mm long) which migrate through the mucosa, reach the bloodstream, and are carried to various muscles. Here they pass into a cystic stage (the cyst being formed by the host), in which they remain until they are swallowed by some flesh-eating host or until they calcify and degenerate. In the intestine of the new host they reach sexual maturity and produce a new lot of larvae, which in turn migrate to the muscles.
The normal hosts are carnivores (dogs and cats). Rodents may be infected, and rats can be a source of infection to pigs. Man may be infected from the pig. (See under TRICHINOSIS.)
Stephanurus dentatus is a thickish worm of fair size, the male being nearly 3 cm long and the female a little larger. It is found as a rule in the kidney fat of pigs, but also occurs in the liver and other locations in these animals and in ruminants. It is found in America and Australia, and is responsible for considerable damage. Its life-cycle is similar to that of the hookworms. Thiabendazole, fenbendazole and ivermerctin have proved effective in controlling this parasite.