[LINK] "Analysis clarifies route of AIDS"

[rfmcdonald]

From the Los Angeles Times:

A genetic analysis of 25-year-old blood samples has outlined a new map of the AIDS virus' journey out of Africa, showing that today's most widespread subtype first emerged in Haiti in the 1960s and arrived in the United States a few years later.

The analysis fills in a gap in the history of the virus, whose migration has been known in only sketchy form from its origin in Africa in the 1930s to its first detection in Los Angeles in 1981.

[. . .]

The analysis, published today in the Proceedings of the National Academy of Sciences, focused on a variety of HIV known as subtype B, the most prevalent form in most countries outside of Africa.

Michael Worobey, an evolutionary biologist at the University of Arizona and senior author of the study, analyzed five blood samples collected in 1982 and 1983 from Haitian AIDS patients in Miami.

The samples were held in frozen storage by the national Centers for Disease Control and Prevention.

Worobey and his colleagues looked at two viral genes and compared their sequences with viruses from around the world.

As a baseline, they used virus samples from Central Africa that are considered some of the earliest forms of the human immunodeficiency virus .

Because viruses constantly mutate, researchers could construct a rough timeline of development by measuring how much the genes in more recent samples had drifted away from their ancestral forms.

The team found that the Haitian samples were genetically the most closely related to the African virus, indicating that they were among the earliest to branch off.

Statistically, researchers found a 99.7% certainty that HIV subtype B originated in Haiti, Worobey said.

Worobey surmised that the virus was brought to Haiti by workers who had gone to the Democratic Republic of Congo, formerly known as Zaire, after it became independent in 1960. The virus appears to have been carried to the United States by Haitian immigrants between 1966 and 1972, according to the mutation timeline.

As Reuters' article on the subject points out, and as this Aidsmap article from March made clear, it looks very much like it took only a single person, travelling from the Democratic Republic of Congo to Haiti, to transport HIV-1 to that Caribbean country.

They found that HIV was brought to Haiti by an infected person from central Africa in about 1966, which matches earlier estimates, and then came to the United States in about 1969.

The researchers think an unknown single infected Haitian immigrant arrived in a large city like Miami or New York, and the virus circulated for years -- first in the U.S. population and then to other nations.

It can take several years after infection for a person to develop AIDS, a disease that ravages the immune system.

"That one infection would have become two, and then it doubles again and the two becomes four," Worobey said. "So you have a period -- probably a fair number of years -- where you're dealing with probably fewer than a hundred people who are infected.

"And then, as with epidemic expansion, at some point the hundred becomes 200, you start getting into thousands, tens of thousands. And then quite rapidly you can be up into the hundreds of thousands of infections that were probably already there before AIDS was recognized in the early 1980s."