<div>Researchers have found evidence that strains of chimpanzee-carried simian immunodeficiency virus (SIV), including those responsible for the global HIV pandemic, can infect human cells.<br /><br />In the early 1900s, probably near a West African rain-forest, it was thought that a hunter or vendor of bush meat - a wild game that can include primates - acquired the first strain of a simian immunodeficiency virus that scientists consider the ancestor of HIV.<br /><br />A new study led by researchers from University of Nebraska-Lincoln in the US supported this hypothesis by showing the first in vivo evidence that strains of chimpanzee-carried SIVs can infect human cells.<br /><br />They include 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 in Africa, researchers said.<br /><br />They also 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.<br /><br />"The question was whether SIV strains that have not been found in humans have the potential to cause another HIV-like infection," said Qingsheng Li from Nebraska Centre for Virology.<br /><br />"The answer is that, actually, they do. They get replicated at a very high level. It is surprising," said Li.<br /><br />Researchers came to the conclusions after inoculating mice that were implanted with human tissues and stem cells, which stimulated the growth of other cells essential to the human immune system.<br /><br />To study why humans have acquired certain HIV strains while avoiding others, researchers injected low doses of the four SIV strains into separate groups of the mice.<br /><br />They found that the inferred SIV forerunners of HIV-1 M and the Cameroon-specific strain required fewer opportunities to infect the mice than did the two SIV strains whose HIV descendants have not been found in humans.<br /><br />According to Li, this may stem from the fact that the genetic makeup of the latter two strains differs more from HIV-1 M than does the Cameroon strain, which shares more genes with its pandemic cousin.<br /><br />"Based on our experiments, we clearly see some differences between the strains. That implies that there might be differences in the likelihood of cross-species transmission when a person is exposed to one strain versus another," said Li.<br /><br />Researchers also found evidence for the long-suspected notion that SIV strains mutate upon entering cells to overcome human-specific barriers to infection.<br /><br />Within 14 weeks, the same viral gene in two different SIV strains - including the ancestor of HIV-1 M - regularly underwent mutations at two key positions on that gene.<br /><br />The experimental approach employed by researchers could help assess the threat posed by additional SIVs and numerous other animal-carried virus.<br /><br />The findings were published in the Journal of Virology.</div>
<div>Researchers have found evidence that strains of chimpanzee-carried simian immunodeficiency virus (SIV), including those responsible for the global HIV pandemic, can infect human cells.<br /><br />In the early 1900s, probably near a West African rain-forest, it was thought that a hunter or vendor of bush meat - a wild game that can include primates - acquired the first strain of a simian immunodeficiency virus that scientists consider the ancestor of HIV.<br /><br />A new study led by researchers from University of Nebraska-Lincoln in the US supported this hypothesis by showing the first in vivo evidence that strains of chimpanzee-carried SIVs can infect human cells.<br /><br />They include 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 in Africa, researchers said.<br /><br />They also 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.<br /><br />"The question was whether SIV strains that have not been found in humans have the potential to cause another HIV-like infection," said Qingsheng Li from Nebraska Centre for Virology.<br /><br />"The answer is that, actually, they do. They get replicated at a very high level. It is surprising," said Li.<br /><br />Researchers came to the conclusions after inoculating mice that were implanted with human tissues and stem cells, which stimulated the growth of other cells essential to the human immune system.<br /><br />To study why humans have acquired certain HIV strains while avoiding others, researchers injected low doses of the four SIV strains into separate groups of the mice.<br /><br />They found that the inferred SIV forerunners of HIV-1 M and the Cameroon-specific strain required fewer opportunities to infect the mice than did the two SIV strains whose HIV descendants have not been found in humans.<br /><br />According to Li, this may stem from the fact that the genetic makeup of the latter two strains differs more from HIV-1 M than does the Cameroon strain, which shares more genes with its pandemic cousin.<br /><br />"Based on our experiments, we clearly see some differences between the strains. That implies that there might be differences in the likelihood of cross-species transmission when a person is exposed to one strain versus another," said Li.<br /><br />Researchers also found evidence for the long-suspected notion that SIV strains mutate upon entering cells to overcome human-specific barriers to infection.<br /><br />Within 14 weeks, the same viral gene in two different SIV strains - including the ancestor of HIV-1 M - regularly underwent mutations at two key positions on that gene.<br /><br />The experimental approach employed by researchers could help assess the threat posed by additional SIVs and numerous other animal-carried virus.<br /><br />The findings were published in the Journal of Virology.</div>