We describe a laboratory model using Eimeria falciformis and E. pragensis to investigate some of the interactions in double-species infections of Eimeria. Mice were given trickle infections by oral inoculation of 100 sporulated oocysts of one species at 3 or 4 day intervals throughout the experiments and, once immunity had developed, as indicated by cessation of oocyst production, the animals were challenged with a single inoculation of the other species. A trickle infection of E. falciformis gave a significant enhancement of oocyst output from E. pragensis infection as compared with animals that had not received E. falciformis. Histological examination of the mice infected with E. pragensis showed significantly more asexual parasites and a significantly higher female/male ratio in the mice that had received trickle E. falciformis infections than in those that had not. There was no evidence to suggest that extra asexual generations were occurring in these mice. In the converse experimental protocol, trickle E. pragensis infections had no significant effect on a single E. falciformis infection. We discuss the possible mechanisms for the interactions and also how these interactions may influence multiple species infections in animals in their natural habitats.

A trickle infection experiment was undertaken to study in detail the population dynamics of Oesophagostomum dentatum in pigs. Three groups of 32 pigs were inoculated via the feed twice weekly with 100 (Group A), 1000 (Group B) or 10000 (Group C) O. dentatum infective larvae (L3). Five pigs from each group were killed 2, 4, 8, 12, 16, and 20 weeks after the first inoculation (p.i.) to determine their worm burdens. Weekly faecal egg counts were determined. At slaughter, worms were counted, differentiated according to sex and developmental stage, and their length measured. Faecal egg counts ranked with dose rate until week 15, but later were more variable. The proportion of the total number of L3 administered which were recovered at slaughter inversely ranked with dose rate. In group C it decreased over time, whereas in groups A and B there was no consistent pattern. Worm fecundities (epg/female) in groups A and B were higher than in group C. The lengths of the female worms increased over time, whereas the lengths of the male worms remained approximately constant from week 8. The study suggests reduced establishment of incoming larvae and lower fecundity of the female worms at high dose levels.