Precursor to H.I.V. Was in Monkeys for Millennia (NY Times)

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Precursor to H.I.V. Was in Monkeys for Millennia

By DONALD G. McNEIL Jr.

In a discovery that sheds new light on the history of AIDS, scientists have

found evidence that the ancestor to the virus that causes the disease has been

in monkeys and apes for at least 32,000 years — not just a few hundred years, as

had been previously thought.

That means humans have presumably been exposed many times to S.I.V., the simian

immunodeficiency virus, because people have been hunting monkeys for

millenniums, risking infection every time they butcher one for food.

And that assumption in turn complicates a question that has bedeviled AIDS

scientists for years: What happened in Africa in the early 20th century that let

a mild monkey disease move into humans, mutate to become highly transmissible

and then explode into one of history's great killers, one that has claimed 25

million lives so far?

Among the theories different researchers have put forward are the growth of

African cities and the proliferation of cheap syringes.

Confirming that the virus is very old also helps explain why it infects almost

all African monkeys but does not sicken them. Over many generations, as any

disease kills off vulnerable victims, the host adapts to it.

The new research, published Thursday in Science magazine, was relatively simple.

Scientists tested 79 monkeys from Bioko, a volcanic island 19 miles off the West

African coast. Bioko used to be the end of a peninsula attached to the mainland

in what is now Cameroon, but it was cut off when sea levels rose 10,000 years

ago at the end of the last ice age.

Since then, six monkey species have developed in isolation on the island, and

scientists from the National Primate Research Center at Tulane University in

Louisiana and other American and African universities found that four of them —

drills, red-eared guenons, Preuss's guenons and black colobuses — had members

that were infected with S.I.V.

The four strains in the four species were genetically very different from one

another — meaning they presumably did not come from monkeys carried over to the

island by humans in the last few centuries. But each was close to the strain

infecting members of the same four genuses on the mainland, meaning they must

have existed before Bioko was cut off.

Knowing that all four strains were at least 10,000 years old, scientists

recalculated the virus's " molecular clock, " measuring how fast it mutates. They

now believe that all the S.I.V. strains infecting monkeys and apes across Africa

diverged from a common ancestor between 32,000 and 78,000 years ago.

" When we only had 25 years of data, we were dating from the tip at the end of a

branch of the evolutionary tree, " said Preston A. Marx, a virologist at the

Tulane primate center and an author of the paper in Science. " I knew that what

we had before couldn't be right, because the virus had spread from the Atlantic

to the Indian Ocean to the southern end of the continent, and it couldn't have

done that in a couple of hundred years. "

Beatrice H. Hahn, a virologist from the University of Alabama at Birmingham and

a discoverer of the simian virus, called the study " a very nice paper, " adding,

" This is what people like us have been looking for. "

Previous methods of dating the virus had concluded it was a few hundred to 2,000

years old, " and that just didn't seem right, " Dr. Hahn said.

The ancestor virus — which, like many diseases, may have crossed into simians

from another, still-unknown species — may have existed for millions of years.

That theory was given greater credence two years ago with the discovery that

some Madagascar lemurs have in their genomes the remnants of a virus that was

not an S.I.V., but related to it. Madagascar, a Texas-size island 250 miles off

the southeastern African coast, separated from Africa 160 million years ago. It

has no monkeys, but lemurs' ancestors arrived there, possibly on floating mats

of vegetation, probably more than 10 million years ago.

H.I.V., which is almost universally fatal to humans, is obviously very new to

us. As Dr. Marx pointed out, if it had been in humans before the 20th century,

it would have arrived in the Americas in some of the 12 million Africans

kidnapped for the slave trade.

Its immediate ancestor is probably also relatively new to chimpanzees. Last

year, Dr. Hahn showed that it can sicken and kill chimps, although not as

quickly, meaning they have probably been adapting to it for generations.

The virus has probably crossed over from simians into humans at least five

times. There are two human immunodeficiency viruses, H.I.V.-1, by far the most

common, and H.I.V.-2, which is milder and rarely seen outside West Africa, and

which jumped to humans from sooty mangabeys, a monkey that West Africans hunt

and eat.

H.I.V.-1, in turn, has four substrains, designated M, N, O and P. The first,

which has spread around the world, clearly came from chimpanzees, as did N and

O. But P appears to have crossed over from a gorilla; it was discovered only

last year, and in only one woman, who was from Cameroon, where lowland gorillas

are hunted for meat.

It is very likely, scientists said, that a little infected monkey or ape blood

got into human veins many times in history as hunters cut themselves while

butchering carcasses. But even if it sickened those hunters, it probably died

out with them or their immediate contacts.

The earliest confirmed H.I.V. case in humans was found in blood drawn in 1959

from a man in Kinshasa, in what was then called the Belgian Congo.

Sometime between the 1800s and 1959, something presumably allowed a human

infection with a chimpanzee virus to spread widely enough to evolve into modern

H.I.V.-1, which could spread easily among humans.

Dr. Marx believes that the crucial event was the introduction into Africa of

millions of inexpensive, mass-produced syringes in the 1950s. Campaigns to wipe

out yaws, syphilis, malaria, smallpox and polio required syringes, and many were

reused, often with official approval. Traditional healers adopted them for

injecting their decoctions, and they became status symbols; a study in Uganda in

the 1960s found that 80 percent of families owned one.

Not everyone agrees. Worobey, a virologist at the University of Arizona

and another author of the Science paper, said backdating the molecular clock,

which he did by comparing the 1959 blood sample with the only other known early

one — a paraffin-embedded lymph node from 1960, also from Kinshasa — suggested

that the virus emerged closer to 1910, when syringes were handmade, expensive

and rare.

He and Dr. Hahn suspect that the growth of colonial cities is to blame. Before

1910, no Central African town had more than 10,000 people. But urban migration

rose, increasing sexual contacts and leading to red-light districts.

http://www.nytimes.com/2010/09/17/health/17aids.html