Volume 1

Plant and animal biology / by A.E. Vines and N. Rees.

  • Vines, A. E. (Albert Edward)
Date:
1972
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Plant and animal biology / by A.E. Vines and N. Rees. Source: Wellcome Collection.

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    the bile ducts affects digestion, and the excretory products of the flukes have a poisoning effect. In a serious infection, the condition of “liver rot” results; the liver is eroded into a broken mass of tissue, the sheep suffers from great muscular weakness and there is severe dropsy. In some regions, the loss of life is considerable. Control Measures A knowledge of the life history again indicates the best point at which to attack the parasite. Wet pastures, which harbour the snails, are obviously conducive to the spread of the infection, and therefore, draining of sheep pasture is the most suitable measure of protection for the flocks. In the hill pastures, this is often impossible and it has been found profitable to introduce ducks and geese to eat the snails. Various drugs are used on the infected animals, but they do not have considerable effect. It has been found that the “eggs” of F. hepatica will not hatch in water which is more alkaline than pH 7-5 and therefore the plentiful use of lime on pastures might have a beneficial effect. General Remarks Although man may be infected with liver flukes by drinking water which contains the cercariae, such cases are rare. There are several flukes which have more serious consequences. Among them are the blood flukes of the genus Schistosoma , and the Chinese liver flukes, Clonorchis [Opisthorchis] sinensis. Adult schistosomes live in the abdominal veins of man, the female being carried permanently in ventral folds of the male body. The eggs are laid in capillaries of the bladder; each possesses a sharp spine which lacerates the wall and thus it is liberated into the urine and passed out of the body. The young stages are passed in a water snail, and man is infected by the cercariae in drinking water or through the skin. Schistosomiasis is a serious disease in the rice-eating people of the East, where the flooded paddy-fields provide ideal conditions for continuous infection. That it is an ancient human disease is proved by the fact that schistosome eggs have been found in Egyptian mummies of a period three thousand years ago. It is estimated that over two hundred million people are seriously affected at the present time. Clonorchis sinensis has three hosts in its life history. The primary host is a mammal, often man, the secondary host is a water-snail and the tertiary host is a freshwater fish. The cercariae from the snail burrow into the muscle of the fish, usually a carp or goldfish, and man is infected by eating raw or insufficiently cooked fish. There is an endless source of infection in the fish-ponds of China and Japan. The interpretation of the multiplicative stages in the young forms of