May Rapoport's rule apply to human associated pathogens?

Many debates surround the generalization of Rapoport's rule (i.e., the presence of a positive correlation between range size and latitude); however, little attention has been devoted to this spatial pattern (1) worldwide and (2) for pathogenic microorganisms. In this study, we analyzed this relationship for 290 human pathogenic species dispersed throughout the world to test whether pathogenic organisms with different ecological niches and strategies will show this trend. The midpoint method was used to calculate the correlation between the geographical range size and the latitude applied to different subsets of pathogens, including taxonomic subdivisions (bacteria, viruses, helminths, protozoans, and fungi) and categories based on transmission mode and host specificity. It is assumed that Rapoport's spatial pattern may exist for human infectious diseases, whatever hemisphere is considered, for 5 to 7 of 8 of the selected groups, depending on the pathogen species included. This is the first study performed to investigate Rapoport's pattern at a global scale for various pathogenic organisms. We also discuss how three well-known spatial patterns of diversity, i.e., latitudinal gradient, nested species pattern, and Rapoport's rule, may vary together to produce the actual large-scale geographical distribution of human pathogenic species observed on Earth. These findings have important messages for understanding the distribution and the diffusion of human pathogenic species; however, further studies are needed to investigate the exact underlying mechanisms responsible for those patterns.