PARASITE EPIDEMIOLOGY AND HOST POPULATION-GROWTH - HELIGMOSOMOIDES POLYGYRUS (NEMATODA) IN ENCLOSED WOOD MOUSE-POPULATIONS

(1) This study examined the interaction between Heligmosomoides polygyrus (Nematoda) and wood mouse, Apodemus sylvaticus, populations housed in large open-air enclosures at Wytham Woods, Oxfordshire, between April 1988 and 1990. (2) Wood mouse reproduction was strongly seasonal and mimicked that of wild populations. Overall, reproduction was not influenced by the presence of the parasite. (3) In contrast, wood mouse survival (from 1 month of age onwards) was compromised in infected mice compared with controls. Survival also varied with month of mouse birth, such that survival was poorest for individuals born in the middle of the breeding season (April-August) and greatest for those born at the end of this period (August-October). (4) Parasite prevalence was 98% and average intensity of infection around 80 worms per mouse. Male mice harboured slightly more parasites than females, although differences were not statistically significant. (5) Parasite burden of individual mice varied greatly, ranging from 0 to 371 worms per mouse, and parasites were highly aggregated or overdispersed within the host population. Overdispersion was similar in both sexes and increased with mouse age. (6) There was a negative correlation between worm burden and mouse age in female, but not in male, wood mice. Parasite fecundity (assessed through parasite gg counts) was not associated with mouse worm burden. (7) Infection of offspring born to 'infected' and 'control' enclosures during May 1990 demonstrated no significant differences in susceptibility to repeated H. polygyrus infection under experimental conditions in the laboratory.