Egg output of Heligmosomoides polygyrus (Nematospiroides dubius) in mice given multiple infections of constant or increasing size.

The effect of repeated infections on the development of gastrointestinal strongyle and on their fecundity was studied using Heligmosomoides polygyrus as an experimental model. Two experiments were carried out: animals were dosed with constant numbers of larvae in the first experiment and with increasing numbers of parasites in the second. Results allowed us to determine the effects of the conditions of infection on the settlement of parasite populations and on their fecundity. Our observations showed that with repeated and increasing infections, the percentage of worms which developed following each ingestion of larvae diminished as the number of ingested larvae increased. When infections stopped the worm burden sharply decreased. The kinetics of egg excretion was comparable to that observed in the case of single infection. Fluctuations of egg excretion were to a large extent related to the variations in size of the worm burden. Finally, the individual fecundity of worms did not seem to fall below a certain value. In these experiments the number of eggs layed per female and per day never fell below 100.