An alternative is to focus on non-pathogen-specific aspects of the host's immune response [16] , detecting the presence of significant microbial infections through perturbations caused in the expression of immunological genes in the host [17] . In the present study we present an example of such an approach, revealing spatio-temporal patterns of immunological expression in a summertime wood mouse population in the UK that may point to epidemic infections with an unknown microbial infectious agent.