Experimental investigation of factors generating aggregation of parasite populations using Heligmosomoides polygyrus (Nematoda) in laboratory mice

The importance of host heterogeneity in generating aggregation was investigated using Heligmosomoides polygyrus (Nematoda) in laboratory mice. The protocol compared parameters of infection between inbred and outbred mice, primary and challenge infections, and gavage and natural exposure, to investigate the relative effects of innate resistance, acquired resistance and behaviour, respectively. The results show that heterogeneity in acquired resistance is the most consistent factor contributing to the variability and aggregation of H. polygyrus. When groups of mice did not acquire resistance, either in certain inbred strains or when mice were immunosuppressed, variability after the challenge was comparable with that after a primary infection. Heterogeneity in host behaviour, particularly in behaviours enhancing skin contact with larvae, frequently increased aggregation above that detected in both primary and challenge infections. Surprisingly, inconsistent results were obtained when inbred and outbred groups of mice were compared. The results suggest that the relative contribution of these three factors is likely to vary spatially and temporally