We have shown here that very distinct anomalies in immunological gene expression patterns can be detected in wild mammal populations if these are surveyed over time. We suggest that such patterns will often be caused by infectious agents and can be used to monitor important infection influences operating on a natural host population. The general approach used here is technically accessible to a wide range of researchers. An obvious extension would also be to combine the present methods with next generation sequencing techniques for the broad detection of microbial pathogens [40, 41] in animals with anomalous immunological transcriptional profiles compared to ''normal'' animals. In the present example, we focussed on a population of wood mice and were able to detect the probable signatures of epidemic infectious disease outbreaks and their demographic and individual correlates. Given the long standing interest in the dynamics of A. sylvaticus populations in the UK [42, 43, 44, 45] , in particular the apparent slow growth during the earlier part of the breeding season, this study might point towards a possible, destabilizing, role for microbial infectious disease in addition to the factors identified by other authors. There is also a wider significance for the ability of ecologists to analyze the dynamic interaction between pathogen communities and their wildlife hosts and, particularly, to identify unsuspected acute microbial infectious disease outbreaks, whose effects might otherwise be dismissed as generalized environmental noise.