In spite of its potential impact on pathogenicity, evolution, epidemiology and control, the distribution of pathogens over their host range and the occurrence of co-infections have been largely overlooked, and most research on pathogen ecology and epidemiology has dealt with specific pathogen-host interactions [8] . To our knowledge, it has not been analysed whether the distribution of pathogens over their host range is random or, alternatively, associations between pathogens and hosts occur, neither has been addressed whether host co-infection by different pathogens is random or associations between pathogens occur in particular hosts. Here we address these issues.