1. Oesophagus and stomach
Gongylonema. Two species occur in ruminants and 1 in pigs. They are found just below the epithelium in the thoracic third of the oesophagus. The intermediate hosts are various species of dung-beetles.
Haemonchus contortus. This is the large stomach worm or ‘barber’s pole’ worm of ruminants, so-called because of the female’s spiral red and white stripes. The male is red. It is a trichostrongyle, with a length of about 30 mm and the thickness of a pin. It is a voracious blood-sucker, and inhabits the abomasum. It can cause serious anaemia and unthriftiness, especially in lambs.
Haemonchus placet is another of several species.
Ostertagia worms, which are of considerable economic importance, are peculiar in that while most infective larvae living in the abomasum moult twice to become adults, some — especially perhaps those ingested by the calf during late summer and autumn — moult only once and remain as 4th-stage larvae in a dormant state. These dormant larvae are unaffected by many anthelmintics but are usually, though not always, susceptible to ivermectin, fenbendazole and albendazole. Later they develop into adults causing a winter outbreak of gastroenteritis. Calves should therefore be dosed in September and moved to ‘clean’ pasture.
Also known as the small brown stomach worm, Ostertagia cause severe irritation of the mucous membrane by the formation of nodules. Infested animals may lose weight, scour, and become anaemic.
2. Small intestine
Ascaris vitulorum. This large round worm of cattle is generally of little importance, but it may be a frequent and fatal parasite of calves in certain localities.
Nematodirus. This is a common trichostrongyle genus found in large numbers in the small intestine of sheep. It is a very slender form under 2.5 cm long. In recent years nematodirus infestation has caused severe losses.
The infestation is a ‘lamb-to-lamb’ one, and can be avoided – where practicable – by confining lambs to pasture which carried no lambs in the previous 2 seasons. Nematodirus species found in Britain are Nematodirus filicollis, Nematodirus helvetianus, Nematodirus spathiges, and Nematodirus battus, Nematodirus helvetianus and Nematodirus battus are parasites of calves. (See PASTURE, CONTAMINATION OF.)
Cooperia species are important. They are usually present in association with other species of worms, e.g. Ostertagia, Trichostrongylus. They seldom cause anaemia, but are responsible for weight loss and scouring. Trichostrongylus worms are very small (only 2 to 7 mm long) and inhabit the abomasum and duodenum.
Bunestomum (hookworms) live in the small intestine. The larvae may either enter their host via the mouth or penetrate the skin. They suck blood and accordingly cause anaemia and sometimes oedema under the throat. (See HOOKWORMS.)
Oesophagostomum. This is a genus of strongyle worms related to the horse forms, and found in ruminants and pigs. They are about 2.5 cm long. They are the cause of nodular disease of the intestine (‘pimply gut’). If present in small numbers, the only result is to render the intestine unfit for sausage skins. If in large numbers, the symptoms are anaemia, emaciation, diarrhoea, and oedema. The disease in this case often has a fatal termination.
Trichuris. This genus of whip-worm occurs in the caecum of various animals, but is usually of little importance. The worms have very slender necks with stoutish bodies. The necks are threaded through the mucous membrane of their host.
They may cause inflammation at the point of insertion of the head and may admit bacteria.
Strongyloides worms are found in the small intestine, often deep in the mucosa. Scouring is caused in heavy infestations. The worm larvae can enter the body via the skin.
Dictyocaulus. Three species are known in cattle, but only 1 is important – Dictyocaulus viviparus, which causes a form of bronchitis. The male is about 4 cm long and the female about 7 cm. Eggs hatch in the lung, and the larvae climbing up the trachea are swallowed, passing to the exterior with the faeces. After moulting twice, they reach the resistant infective stage, and can live thus on pasture through the winter. When swallowed, they continue their development.
The signs and treatment are described under PARASITIC BRONCHITIS.
Parasitic bronchitis (‘husk’) Several species of roundworm occur in sheep and goats.
Dictyocaulus filaria is the largest and most common species. The male is about 5 cm long and the female 8 cm. The infective stage is reached in about 10 days. Apparently lambs can be infected prenatally. This worm is cosmopolitan in its distribution. Its life-history is direct.
The symptoms are those of a verminous bronchitis, sometimes complicated by bacterial infection, but otherwise similar to those in cattle.
Protostrongylus (Synthetocaulus) rufescens is a red and much smaller form. The male is about 2 cm and the female 3 cm long. It is found mainly in Europe. These worms live in the bronchioles and in the pulmonary parenchyma, and cause a verminous lobular pneumonia. The eggs cause a diffuse nodular pneumonia. Cough is less prominent than in the above form, but breathing is difficult.
4. Connective tissues
Onchocerca. Several species occur in cattle in various parts of the world. They are the cause of ‘worm nodules’.
The nodules are found mainly in the brisket, but also occur in the flank and forequarters. They appear to cause little harm to their host, but as the capsule is a product of inflammation, beef containing worm nodules is condemned, and in Australia they have caused considerable loss in the export trade.
Dracunculus. Only 1 species of this worm is found in the domestic animals, Dracunculus medinensis, the guinea worm’. It is found in India, Africa, and South America. The female is of considerable length, but is generally recovered from the host in small pieces. It is milky white in colour, smooth and without markings. Nearly the whole of the worm is occupied by the uterus, packed with coiled-up embryos. The worm occupies a subcuticular site, as a rule in the extremities, with the head-end projecting to the exterior. The larvae are released by a prolapse of the uterus through the cuticle of the worm. They escape into the water, and are swallowed by a cyclops in which they develop. The cyclops is in due course swallowed in the drinking water by a suitable host – practically any of the domestic animals will do – and larvae are released by the digestive juices and proceed to their adult habitats. The worm may give rise to local abscesses, and sometimes affects the feet of dogs.
Thelazia. (See EYEWORMS.)