Human influence small in infectious diseases' distribution: study

Human travel plays a relatively minor role in the distribution of infectious diseases, as it remains restricted by physical and ecological barriers, according to a study released Tuesday by the Imperial College London.

These barriers include oceans, environmental conditions like climate, or the presence of other species that the distribution of infectious diseases depend on, such as insect transmitters or other animal hosts, according to the study. In other words, it is really not that easy for these diseases to spread across the globe.

Looking for clues to explain why some diseases are shared between different countries while others are not, a team of researchers analyzed the distributions of 187 human infectious diseases across 225 countries. They found a pattern that was most similar to the distributions of the regions' plants and animals - the more biodiversity shared between countries, the more diseases are also shared.

"While human activities have certainly contributed to the spread of infectious diseases into new places, on the whole, patterns of human infectious disease still look quite similar to patterns of wildlife biodiversity. This is probably because they follow similar ecological rules," said Dr. Kris Murray, from Imperial College London, who participated in the study.

These rules, such as the diversification, dispersal, and extinction of species, shape global distributions of animal and plant groups. For example, they explain why Australia is home to koalas, while Canada has grizzly bears.

Dr. Murray said: "We're not saying that human travel isn't important - but when you look at all diseases together, the influence of human activities on their distributions still looks surprisingly small. The complete obliteration of biogeographic barriers has not yet occurred, and these will continue to define which diseases occur where in the face of global change. To some extent, their ecologies resist it."

International epidemics, such as SARS, MERS and Ebola really are the rare exceptions to the rule, according to Dr. Murray. Endit