Male organs fertilize female organs in the middle segments of the chain. The eggs burst out of the ripe segments usually when they are shed in the birds' droppings, because most tape worms live in the alimentary canal. Usually, eggs must be eaten by an intermediate host of another species of animal, before the first stage of development of the parasites can occur. The intermediate host may be an earthworm, snail, slug, insect, fish, or other creature which is edible to birds--the main or primary hosts. The eggs themselves are not infective to the primary host. In the intermediate host, early development into a bladder-worm stage takes place in the muscle or other body tissues, and not in the cavity of the gut from which it quickly migrates after being swallowed. When the infested intermediate host is eaten by a suitable bird host, digestion of the tissues releases the bladder-worm in the gut, which then gives rise to one or more adult tapeworms.
Clinical signs of tapeworm infestation are dullness, loss of appetite, sometimes excessive thirst, loss of weight, anemia and leg weakness. The resulting debility may pave the way for infections and other diseases. Tapeworms also tend to contribute to the misery of birds which are sick from other causes. Nodules are produced in the gut wall by some species of Raillietina which are reminiscent of those caused by tuberculosis, this being one of the few genera producing obvious disease changes in birds.
Treatment and control:
Grain and seed eaters are much less likely to become infested than insectivorous birds, although at times they may eat certain types of small animal life which act as intermediate hosts. Lack of knowledge about the life histories of many tapeworms in birds is so great that it is often impossible to determine where, when, and how infestation occurred. As a result, few recommendations can be made to limit re-infestation. Attention to general hygiene may help by limiting spread of shed tapeworm ova in droppings by flies, beetles, ants and other invertebrates. On the other hand, eliminating these tasty morsels, which can be a useful source of animal protein, may be more harmful to the health of the birds than the burden of worms which they may acquire from them. The amount of nutrients which the tapeworms absorb whilst in the gut of the host is negligible. Absorption by the host of waste products and toxins produced by the parasites is almost certainly small, although the effect they have on the bird is unknown.
Avian tapeworms are resistant to drugs. Most of those which have been tried are liable to cause more ill effects than the worms themselves and often leave the head and neck of the worm still in place, capable of growing again to maturity. Such drugs include santonin, felix mas (malefern extract) kamala and carbon tetrachloride. Stannous (tin) tartrate and pelleterine hydrochloride are a little better regarding toxicity and are moderately effective against Raillietina, whilst dichlorophen appears effective against some types of tapeworm. It is preferable, however, to rely on hygiene to reduce the possibilities of infestation and to keep birds well fed, exercised, and content, In fact, treatment should only be attempted when a veterinarian decides that it is necessary, for example following the confirmation at post-mortem examination of heavy infestations of other birds in the same group.
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Hamilton & District Budgerigar Society Inc.