Epidemiology of Heligmosomoides polygyrus in mice: experiments on natural transmission.

An experimental system is described for the study of the community dynamics of helminth-host populations, using Heligmosomoides polygyrus in the laboratory mouse. The results of a preliminary experiment using closed populations of 50 mice revealed that coexistence of host and parasite occurs for at least 4 months in the absence of immigration, with the generation of epidemiological patterns similar to those observed in the real world. In well-nourished mice the prevalence and intensity of infection initially increased with time and then declined, probably as a result of acquired immunity. The prevalence and intensity of infection increased less rapidly among hosts fed on a low protein diet, but continued to rise over the entire duration of the experiment. This continued rise is interpreted as evidence of a negative effect of protein malnutrition on host immunocompetence. The frequency distributions of parasite numbers/host were over-dispersed in each mouse population. No density dependence in parasite fecundity was detected. Aspiculuris tetraptera was also found to be present in the mouse populations. This parasite was not transmitted between mice fed on a high protein diet, but rose to a prevalence of 80% in protein malnourished animals. No association between the intensity of A. tetraptera and H. polygyrus could be detected in individual hosts. The results are discussed in terms of the future potential of the system for the investigation of the role of acquired immunity (and its genetic control) in the generation of epidemiological patterns.