Transfer of Eimeria apionodes from wood mice directly into untreated laboratory mice was unsuccessful but transfer into corticosteroid-treated animals produced an oocyst output, about 1000 times less than that observed from wood mice after a similar inoculum. Repeated passage through corticosteroid-treated laboratory mice resulted in a line adapted to survival in untreated animals. This line was compared with the parent strain maintained in wood mice and some features of the oocyst output patterns, notably the pre-patent period, appeared to be controlled by the host species. The oocyst production of each population was higher in the host species to which it was adapted than in the other host species (P > 0·001). Once adapted to laboratory mice, the line produced insignificantly different levels of oocysts in corticosteroid-treated and untreated animals (P > 0·05).

The first long-term (27 month) survey of single species of Eimeria occurring in a population of Apodemus sylvaticus in the UK showed that Eimeria apionodes, E. hungaryensis and E. uptoni occurred throughout the period whilst E. sp. E. was only found during 4 months. In first-captured animals, overall prevalence of Eimeria spp. was 73%: a figure higher than previously published, but possibly an underestimate. Multiple infections (2 or 3 species) occurred in 34% of first-capture infected animals, but without significant associations. There were no significant differences of prevalence rates between the sexes, nor between adults and juveniles, except for E. uptoni which was more common in juveniles than in adults. E. hungaryensis and E. uptoni probably occurred as near-continuous infections whilst E. apionodes occurred more intermittently but with no long-term total immunity. Monthly prevalence data indicated ongoing trends over the 27 months. Prevalences of E. apionodes indicated an annual cycle, lowest in January–May and with a peak in October–November, correlating positively with both the number of animals and the percentage of juveniles in the host population and also with the environmental relative humidity. There was no consistent pattern for E. uptoni and an annual cycle for E. hungaryensis was not apparent.