"It is in all our interests to put into place economic alternatives to help people move away from hunting and eating these animals," said Dr Nathan Wolfe, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.

"In addition to preserving endangered species, such development efforts will reduce the ongoing cross-species transmission of retroviruses and other pathogens that could spark future epidemics similar to HIV," he added.

In a collaborative effort, Wolfe and colleagues from the Cameroon Ministry of Health, the US Centers for Disease Control and Prevention and other institutions traced the transmission of an infection called simian foamy virus (SFV).

Like HIV, which causes AIDS, SFV is a retrovirus that can integrate its genetic material into the genome of its human host.

"We're showing that these retroviruses are regularly crossing into humans," Wolfe, who reported the findings in The Lancet medical journal, said in an interview.

"Transmission of retroviruses to humans is not limited to a few isolated occurrences which led to HIV. This is a regularly occurring phenomena," he added.

Scientists know from historical evidence that these types of viruses have the potential to cause a pandemic. HIV is thought to have been transmitted in a very similar way.

The scientists found antibodies for SFV in one percent of 1,099 people from nine rural villages in Cameroon that they had tested who had been exposed to non-human primate blood.

The villagers were infected with multiple forms of SFV from distinct primate species. Infections were from several different areas which suggests the cross-species transmission of these viruses is widespread.

"From our perspective, I think we are talking about the tip of the iceberg," Wolfe added.

New diseases, including AIDS, SARS, Ebola and birdflu, have resulted from infections in animals that have crossed into humans.

But reducing the hunting of primates could prove difficult because bushmeat is a multi-million dollar industry and a key source of food and livelihood for poor people.

In a commentary on the research, Dr Martine Peeters, of the Institute for Research and Development in Montpellier, France said infections from animals are among the most important public health threats facing humanity.