Why 30 years of AIDS is only the tip of an iceberg - 14th Apr 2011

JUNE marks 30 years since the first report of AIDS - a syndrome that has killed an estimated 25 million people worldwide. Yet this year's anniversary is somewhat arbitrary: the virus responsible for AIDS has probably been circulating within human populations for 100 years. Why did it take so long to detect it?

In June 1981, doctors reported an unusual type of pneumonia in five previously healthy young homosexual men in Los Angeles. Two years later the cause of their immunodeficiency was identified: a retrovirus that targets white blood cells, subsequently named human immunodeficiency virus (HIV).

Similarities with the simian immunodeficiency virus (SIV) that infects chimpanzees in west-central Africa suggest the original source of the infection, which probably spread to people who hunted and ate the apes.

Thanks to two chance finds in medical samples collected 50 years ago in what is now the Democratic Republic of the Congo (DRC), we even know roughly when HIV arrived. In 1998, researchers found HIV in a blood sample collected in 1959. This was followed in 2008 by a second discovery of the virus in a sample collected from a woman's lymph node in 1960. The two viruses were subtly different due to their independent evolutionary histories. Comparing their gene sequences established that they likely diverged from a single common ancestor between 1902 and 1921, suggesting HIV has been in human populations for at least that long. Gene sequences also reveal that HIV spread from Africa to Haiti - probably shortly after what is now the DRC gained independence from Belgium in 1960 - and arrived in the US around 1969. Read More