The influence of nutrition on the relationships between gastro–intestinal parasites and their hosts

Abstract

Nutrition experiments tend to be laborious and exacting as do those involving parasitic worms. It is understandable, therefore, that experimental work on the nutrition of parasitized animals has been carried out by relatively few workers and in consequence the data upon which we may assess the interaction of nutrition and parasitism are relatively few. Most of the studies in this field have been with gastro-intestinal parasites and this review will refer mainly to work on the gastro-intestinal parasites of the domestic animals. Our knowledge of the nutrition of parasites is at present fragmentary so that there is little information from which it might be possible to deduce the effects a parasite might have on the nutrition of its host. Usually the volume of the parasite burden, even of a heavily infected animal, is small in comparison with the size of the host and it is difficult to believe that the needs of the parasite for carbohydrate, protein or fat exert an appreciable influence on the amounts of these substances available to the host. I t is possible, however, that parasites require relatively large quantities of vitamins and trace elements and by preferential absorption from the chyle deprive the host of some of them. It has been shown by Nyberg (1952) that Diphyllobothrium latum is a rich source of cyanocobalamin, and von Bonsdorff & Gordin (1952) have suggested that the tapeworm absorbs large amounts of this vitamin causing a macrocytic anaemia in the host. This anaemia can be cured by the administration of dried D. latunz or of cyanocobalamin. More detailed work on the metabolism of nematodes may reveal other instances in which the particular needs of the parasite for vitamins and trace elements conflict with the needs of the host. Effect of parasitic infection on appetite One of the striking effects of gastro-intestinal parasites on their hosts is a depression of appetite. Amongst the first workers to demonstrate this effect were Lucker & Neumayer (1947) who reported a decrease in hay consumption by sheep 6 weeks after the administration of Bunostunium trigonocephalum larvae. Laurence, Groenewald, Quin, Clark, Ortlepp & Bosman (I 95 I) working with 7-month-old lambs infected with Haemonchus contortus and Oesophagostonium columbianum demonstrated a distinct depression of appetite from the 10th day after the administration of infective larvae. Further experiments showed that although the appetite for hay was depressed the total ration of maize, 400 g/sheep to one group and IOO g/sheep to another, was consumed. These results were supported in part by those of Gibson (195 5) who demonstrated that lambs carrying heavy infections of Trichostrongylus axei consumed less hay than uninfected lambs whether they were receiving concentrates or not. He also demonstrated a decreased appetite for concentrates in lambs allowed free access to both hay and concentrated food. I n further observations it