Patterns of parasite aggregation in the wild European rabbit (Oryctolagus cuniculus)

Understanding the factors controlling the distribution of parasites within their host population is fundamental to the wider understanding of parasite epidemiology and ecology. To explore changes in parasite aggregation, Tayl or's power law was used to examine the distributions of five gut helminths of the wild rabbit. Aggregation was found to be a dynamic process that vari ed with year, season, host sex, age class, and myxomatosis. Yearly and seas onal changes are thought. in the main, to be the result of variations in we ather conditions acting upon infectious stages (or intermediate hosts). Evi dence in support of this was the comparatively low degree of fluctuation in the aggregation of the pinworm, Passalurus ambiguus, as the infectious sta ge of this parasite is likely to be less susceptible to environmental varia tion. Host age had a marked effect on the level of aggregation of all paras ites, but this effect varied between parasite species, P. ambiguus, Trichos trongylus retortaeformis and Cittotaenia denticulata aggregation were lower in adult than juvenile rabbits whilst Graphidium strigosum and Mosgovoyia pectinata aggregation tended to increase with age. Host immunity is thought to be responsible for these differences. Differences in aggregation for di fferent parasites were also seen when the rabbit population was split into males and females. Myxomatosis had a marked effect on helminth distribution with substantially less aggregation in rabbits showing clinical signs of t he disease. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.