This map, just published in the American Naturalist by Kate Jones of University College, London, and her colleagues, shows, for any given part of the world, how many viral diseases bats and people share. That bats are reservoirs of illnesses which also affect people was brought to general attention by the recent outbreak of Ebola fever in west Africa. Ebola is spread by bats and, as the map shows, tropical Africa is the place with the greatest number of shared diseases. Dr Jones and her team used these data, culled from 453 studies carried out since the beginning of the 20th century, as the foundation of a model that also looked at things like population density and farming practices to pick out those areas at greatest risk of interspecies transmission. Adding these other factors in showed that a second risky place is south-eastern Asia, including south China. This was the point of origin of another disease outbreak, that of SARS (severe acute respiratory syndrome) in 2002.