When it comes to infectious diseases, no line exists between wild animals and humans.

Jonathan Davies, a scientist at the National Center for Ecological Analysis and Synthesis at UCSB, said he and a team of researchers discovered that closely related species — such as humans and chimpanzees — often share similar pathogens, which is a disease holding organism, ranging from bacterium to viruses. Davies, who was also the lead author of the study, said pathogens often jump species barriers, which he said explains how AIDS spread from chimpanzees to humans.

The team also found that viruses are more likely to jump to species living in close proximity, which means they can jump between distantly related species, Davies said.

“Viruses evolve much faster, so they can adapt more rapidly from different hosts, so they have short generation times, so they can find cracks in the new hosts’ armor and infect them,” he said.

Therefore, because avian influenza is a bird flu virus, it was easily able jump from birds to humans, Davies said. In addition, he said an increase in outbreaks is likely due to new viral diseases in previously sparsely populated areas, particularly in Central and West Africa.

Because there is a high diversity of species in Africa and vegetation is being cut down so more humans can live in formerly rural lands, Davies said contact will increase between animals and humans, meaning that disease is more likely to cross over between species. One way disease will spread will be through bush meat hunting, he said.

“[Bush meat hunting] is hunting wild animals for food,” he said. “It can be a large portion of people’s diet, so they kill all the animals they can find, and cook it for supper.”

Hunting involves a lot of “blood and guts,” Davies said, which makes it a high risk for disease because many pathogens are transmitted through blood.

Davies said the team studied pathogens in gorillas and other primates — humans’ closest relatives — for about four years. Most of the data used was previously collected from Conservation International, a nonprofit organization aimed at protecting biodiversity, and the study was published online last Wednesday in Proceedings of the Royal Society B, he said.