A new study has said that West and Central Africa are emerging as the major sources for the next infectious disease to plague man.

Deforestation in these regions is forcing wild animals that are a natural host for pathogens into ever smaller areas and into ever likelier contact with fast-growing human populations, it said.

The paper, published in the British journal Proceedings of the Royal Society B, looks at how new, killer diseases such as AIDS, Ebola and bird flu have leapt the species barrier to humans in the past three decades.

Its authors found that closely related primates -- monkeys, chimpanzees, gorillas and humans -- pose the biggest risk of "host shift" as they share similar biology and immune responses, and are vulnerable to many of the same microbes.

The similarity is especially strong with chimpanzees, our closest genetic relatives, with whom we shared a common ancestor about 8.6 million years ago.

Humans are almost four times likelier to share pathogens with chimpanzees than with colobus monkeys, which branched from the family tree 34.4 million years ago, says the study.

The virus for acquired immune deficiency syndrome was probably transmitted to humans from a chimpanzee infected with a simian form of AIDS, previous studies have said. More than 25 million people have died of the disease since it was first reported in 1981.

But being distantly related is not a safeguard, either, the new study says.