New York, Jul 22 (IANS): While the HIV epidemic continues to threaten health and well-being of a large section of the world's population, scientists have warned that new forms of the virus jumping from animals to humans cannot be ruled out.

The suggestion stems from a study in which the scientists discovered the first in vivo evidence that strains of chimpanzee-carried simian immunodeficiency virus (SIV) that virologists consider the ancestor of HIV can infect human cells.

"The question was whether SIV strains that have not been found in humans have the potential to cause another HIV-like infection," said senior author Qingsheng Li, Associate Professor at University of Nebraska-Lincoln in the US.

"The answer is that, actually, they do. They get replicated at a very high level. It's surprising," Li said.

The researchers found that the SIV ancestor of HIV-1 M - the strain responsible for the global HIV pandemic - and another ancestral strain of HIV found only among residents of Cameroon can jump from animals to humans.

The researchers further discovered that the SIV ancestors of two HIV strains not identified in humans also managed to invade human cells after multiple exposures in the lab.

The findings appeared in the Journal of Virology.

"The emergence and re-emergence of infectious diseases has become a constant threat to global health, social stability, safety and economic systems," Li said.

The experimental approach employed by the team could help assess the threat posed by additional SIVs and numerous other animal-carried viruses, lead author Zhe Yuan, doctoral student at University of Nebraska-Lincoln.

This could prove especially vital given the dynamic nature of HIV and other zoonotic diseases, he said, many of which have caused new epidemics or even pandemics.

"I think this analysis of the disease is very important for public health," said Yuan, noting that a new group of HIV strains was discovered in 2009.