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The Egg-Laying Function of a Nematode as Shown by Study of Nematodirus Eggs in Utero

1941; American Society of Parasitologists; Volume: 27; Issue: 6 Linguagem: Inglês

10.2307/3272523

1937-2345

J. H. Tetley,

Helminth infection and control

At present, methods do not exist for measuring exactly the pitch of the host-parasite relationship at one point of time. Vague indications of the potential of the relationship have been obtained by observing (1) the ability of parasites to survive, (2) the size to which parasites have grown, (3) the effects of the parasites on the host over a period of time, (4) the feeding of the parasites, and (5) the fecundity of parasites as shown by fecal egg numbers, these latter being expressed either as an empirical figure or as a mean for the population. The degree to which the various functions of the parasites are related to those of the host-parasite relationship seems still to be largely unknown. It would be expected that they would be linked. Thus, in connection with egg-laying of many parasites, from the standpoint of quantity of eggs produced, or the total bulk of such eggs, it would appear that egg-laying has a relationship to the feeding of the worms, proceeding either simultaneously or alternately at short intervals, with feeding. To the extent therefore that extraction of food from the host is responsible for the effects, fecundity must be regarded as an index of these effects. Support for this is provided by Stoll and Tseng (1925), who found that the production of eggs by hookworms, indicated by per gram fecal counts, paralleled clinical symptoms of disease caused by these parasites as measured by lowered hemoglobin or blood loss. Then again from the viewpoint of host resistance or the favorability of the host for the parasite, egg production has been used as an index. Stoll (1929), with Haemonchus contortus, the same author (1932) and Sarles (1932), with Trichostrongylus calcaratus, were early in the field to investigate the host-parasite relationship by following the egg production of parasites. In the belief, therefore, that closer study of egg production by parasites would result in knowledge that might aid in the measurement of the pitch of the host-parasite relationship, an examination has been made of the uterine egg populations of Nemnatodirus species in sheep. Graham (1938) has investigated the fecundity over a period, of single individuals of Strongyloides ratti. The present approach, in essentials, is complementary to this work in that the egg output of whole populations at one point of time has been considered. Nematodirus species were found a convenient experimental medium.