Inferring infection processes of a parasitic nematode using population genetics

The distribution of genetic differentiation in a population of the parasiti c nematode Strongyloides ratti divided between rat hosts was determined. We applied population genetic theory to these data to determine the source of new infections. We estimate the rate at which a rat acquires a new infecti on from (a) the existing subpopulation of parasites within that rat ('self- reinfection') versus (b) the wider environment ('immigration'). We find tha t the observed levels of genetic diversity and differentiation in the study population are consistent with low to moderate rates of self-reinfection a nd inconsistent with high rates of self-reinfection.