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AIDS virus ancestor over 32,000 years old, study finds

Sept. 20, 2010
Courtesy of the University of Arizona
and World Science staff

A new study shows that the mon­key ver­sion of the vi­rus be­hind AIDS is at least 32,000 years old, sci­en­tists say. The find­ing sug­gests that the hu­man ver­sion of the path­o­gen won’t stop kill­ing an­y­time soon, they add.

The re­search shows that it could have tak­en mil­len­nia for mon­keys to de­vel­op re­sist­ance to the le­thal ef­fects, the re­search­ers in­volved in the study ex­plained. If so, they went on, the same might be true for hu­ma­ns.

The re­search, by sci­en­tists at the Uni­vers­ity of Ar­i­zo­na and Tu­lane Uni­vers­ity in New Or­leans, ap­pears in the Sept. 17 is­sue of the jour­nal Sci­ence.

The study shows that the mon­key-infecting path­o­gen, the sim­i­an im­mun­od­e­fi­cien­cy vi­rus or SIV, is at least 32,000 to 75,000 years old, and likely much old­er, mem­bers of the group said. They based their con­clu­sions on a ge­net­ic anal­y­sis of un­ique SIV strains found in mon­keys on Bioko Is­land, a form­er pen­in­su­la that sep­a­rat­ed from main­land Af­ri­ca af­ter the Ice Age more than 10,000 years ago. 

The vi­rus was pre­vi­ously thought to be a few hun­dred years old.

SIV does­n’t cause AIDS in most of its pri­mate hosts, sci­en­tists say, but it prob­a­bly once did. Many vi­ruses grad­u­ally evolve to be­come fairly harm­less, as the more vul­ner­a­ble hosts die out, leav­ing only re­sist­ant popula­t­ions be­hind. This pro­cess can be good for the vi­rus, too, as a dead host may not be very use­ful to a vi­rus.

The new find­ings, if cor­rect, could in­di­cate that it could have tak­en thou­sands of years for SIV to evolve in­to a pri­marily non-le­thal state. Thus the same may be true of the hu­man ver­sion, called hu­man im­mun­od­e­fi vi­rus or HIV, ac­cord­ing to the au­thors.

“HIV is the odd man out,” be­cause most oth­er vi­ruses of its type, called im­mun­od­e­fi­cien­cy vi­ruses, “im­pose a much low­er mor­tal­ity,” said Uni­vers­ity of Ar­i­zo­na bi­ol­o­gist Mi­chael Worobey, who co-led the stu­dy.

“So, if SIV en­tered the pic­ture rel­a­tively re­cently as was pre­vi­ously thought, we would think it achieved a much low­er vir­u­lence over a short timescale,” Worobey said. “But our find­ings sug­gest the op­po­site. If HIV is go­ing to evolve to low­er vir­u­lence, it is un­likely to hap­pen an­y­time soon.”

The study al­so raises a ques­tion about the or­i­gin of HIV, which sci­en­tists be­lieve evolved from SIV. If hu­ma­ns have been ex­posed to SIV-infected mon­keys for thou­sands of years, why did the HIV ep­i­dem­ic only beg­in in the 20th cen­tu­ry?

“Some­thing hap­pened in the 20th cen­tu­ry to change this rel­a­tively be­nign mon­key vi­rus in­to some­thing that was much more po­tent and could start the ep­i­dem­ic. We don’t know what that flash­point was, but there had to be one,” said vi­rol­o­gist Pres­ton Marx of Tu­lane Uni­vers­ity, the oth­er co-leader of the stu­dy

Find­ing these vi­rus strains trapped on Bioko Is­land set­tles a long-stand­ing de­bate, Worobey said.

“It’s like find­ing a fos­sil­ized piece of vi­rus evo­lu­tion,” he said. “We now have this lit­tle is­land that is re­veal­ing clues about SIV, and it said, ‘It’s old.’ Now we know that hu­ma­ns were al­most cer­tainly ex­posed to SIV for a long time, probably hun­dreds of thou­sands of years.”

“Re­con­struct­ing the ev­o­lu­tion­ary past by com­par­ing the genes of these vi­ruses is like look­ing out on­to the ocean,” Worobey said. “You can see a long way, but you don’t know what lies be­yond the hori­zon.” 

SIV was dis­trib­ut­ed across the Af­ri­can con­ti­nent be­fore Bioko Is­land sep­a­rat­ed from the con­ti­nent about 10,000 years ago, he added. “When that hap­pened, what­ev­er vi­ruses were cir­cu­lat­ing at the time be­came iso­lat­ed from the vi­rus popula­t­ions on main­land Af­ri­ca.”

Marx, a vi­rol­o­gist at the Tu­lane Na­tional Pri­mate Re­search Cen­ter, tested his the­o­ry that SIV had an­cient or­i­gins by seek­ing out DNA sam­ples from mon­key popula­t­ions that had been iso­lat­ed for thou­sands of years. His re­search team col­lect­ed bush meat sam­ples from Bioko Drills, the spe­cies Man­drillus leu­cophaeus. The sci­en­tists found four dif­fer­ent strains of SIV that were ge­net­ic­ally very dif­fer­ent from those found on the main­land. Worobey then com­pared DNA se­quences of the vi­ruses with the as­sump­tion that the is­land strains evolved in isola­t­ion for more than 10,000 years.

The com­put­er mod­el­ing showed the rate of muta­t­ion to be much slow­er than pre­vi­ously thought, in­di­cat­ing that the vi­rus is be­tween 32,000 and 75,000 years old. These dates set a new min­i­mum age for SIV, al­though it’s probably even old­er, Marx said.

Worobey said the study has im­plica­t­ions for a lot of rap­idly evolv­ing path­o­gens.

“Our meth­ods are great to de­scribe and pre­dict the short-term changes of vi­ruses like the flu or HIV, but we need to be skep­ti­cal of in­fer­ences in deep time. We found there is a big dis­con­nect be­tween the rap­id ev­o­lu­tion for which those path­o­gens are fa­mous and the in­cred­i­ble de­gree of con­serva­t­ion we’ve found.”

Anoth­er, sep­a­rate new stu­dy, pub­lished in the Fall is­sue of the Jour­nal of Amer­i­can Physi­cians and Sur­geons, ques­tions wheth­er the HIV vi­rus causes AIDS at all. The pa­per, by Etienne de Har­ven, an emer­i­tus pathol­o­gist at the Uni­vers­ity of Toron­to, is a fruit of a years-long cam­paign by some sci­en­tists who ob­ject to the con­ven­tion­al view that HIV causes AIDS.

De Har­ven ar­gued, among oth­er things, that the HIV vi­rus has nev­er been de­tected di­rectly in tis­sue from a pa­tient. Only indi­rect and un­re­li­a­ble tests have been used, meth­ods that can con­fuse ge­net­ic ma­te­ri­al from a vi­rus with stray DNA from a pa­tient’s own cells, de Har­ven con­tended.

The jour­nal is pub­lished by right-wing med­i­cal or­gan­iz­a­tion, the As­socia­t­ion of Amer­i­can Physi­cians and Sur­geons. The group has al­so pro­mo­ted “Tea Party” prin­ci­ples and contro­versially claimed that U.S. Pres­ident Barack Obama may have won over vot­ers us­ing “a co­vert form of hyp­no­sis” pi­o­neered by an Amer­i­can doc­tor.


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A new study shows that the monkey version of the virus behind AIDS is at least 32,000 years old, scientists say. The finding suggests that the human version of the pathogen won’t stop killing anytime soon, they add. The research shows that it could have taken millennia for monkeys to develop resistance to the lethal effects, the researchers involved in the study explained. If so, they went on, the same might be true for humans. The research, by scientists at the University of Arizona and Tulane University in New Orleans, appears in the Sept. 17 issue of the journal Science. The study shows that the monkey-infecting pathogen, the simian immunodeficiency virus or SIV, is at least 32,000 to 75,000 years old, and likely much older, members of the group said. They based their conclusions on a genetic analysis of unique SIV strains found in monkeys on Bioko Island, a former peninsula that separated from mainland Africa after the Ice Age more than 10,000 years ago. The virus was previously thought to be a few hundred years old. SIV doesn’t cause AIDS in most of its primate hosts, scientists say. But probably, it once did. Many viruses gradually evolve to become fairly harmless, as the more vulnerable hosts die out, leaving only resistant populations behind. This process can be good for the virus, too, as a dead host may not be very useful to a virus. The new findings, if correct, could indicate that it could have taken thousands of years for SIV to evolve into a primarily non-lethal state. Thus the same may be true of the human version, called human immunodeficiency virus or HIV, according to the authors. “HIV is the odd man out,” because most other viruses of its type, called immunodeficiency viruses, “impose a much lower mortality,” said University of Arizona biologist Michael Worobey, who co-led the study. “So, if SIV entered the picture relatively recently as was previously thought, we would think it achieved a much lower virulence over a short timescale,” Worobey said. “But our findings suggest the opposite. If HIV is going to evolve to lower virulence, it is unlikely to happen anytime soon.” The study also raises a question about the origin of HIV, which scientists believe evolved from SIV. If humans have been exposed to SIV-infected monkeys for thousands of years, why did the HIV epidemic only begin in the 20th century? “Something happened in the 20th century to change this relatively benign monkey virus into something that was much more potent and could start the epidemic. We don’t know what that flashpoint was, but there had to be one,” said virologist Preston Marx of Tulane University, the other co-leader of the study Finding these virus strains trapped on Bioko Island settles a long-standing debate, Worobey said. “It’s like finding a fossilized piece of virus evolution,” he said. “We now have this little island that is revealing clues about SIV, and it said, ‘It’s old.’ Now we know that humans were almost certainly exposed to SIV for a long time, probably hundreds of thousands of years.” “Reconstructing the evolutionary past by comparing the genes of these viruses is like looking out onto the ocean,” Worobey said. “You can see a long way, but you don’t know what lies beyond the horizon.” SIV was distributed across the African continent before Bioko Island separated from the continent about 10,000 years ago, he added. “When that happened, whatever viruses were circulating at the time became isolated from the virus populations on mainland Africa.” Marx, a virologist at the Tulane National Primate Research Center, tested his theory that SIV had ancient origins by seeking out DNA samples from monkey populations that had been isolated for thousands of years. His research team collected bush meat samples from Bioko Drills, the species Mandrillus leucophaeus. The scientists found four different strains of SIV that were genetically very different from those found on the mainland. Worobey then compared DNA sequences of the viruses with the assumption that the island strains evolved in isolation for more than 10,000 years. The computer modeling showed the rate of mutation to be much slower than previously thought, indicating that the virus is between 32,000 and 75,000 years old. These dates set a new minimum age for SIV, although it’s probably even older, Marx said. Worobey said the study has implications for a lot of rapidly evolving pathogens. “Our methods are great to describe and predict the short-term changes of viruses like the flu or HIV, but we need to be skeptical of inferences in deep time. We found there is a big disconnect between the rapid evolution for which those pathogens are famous and the incredible degree of conservation we’ve found.” Another, separate new study, published in the Fall issue of the Journal of American Physicians and Surgeons, questions whether the HIV virus causes AIDS at all. The paper, by Etienne de Harven, an emeritus pathologist at the University of Toronto, is a fruit of a years-long campaign by some scientists who object to the conventional view that HIV causes AIDS. De Harven argued, among other things, that the HIV virus has never been detected directly in tissue from a patient. Only indirect and unreliable tests have been used, and these methods can confuse genetic material from a virus with stray DNA from a patient’s own cells, de Harven contended. The journal is published by right-wing medical organization, the Association of American Physicians and Surgeons. The group has also controversially claimed that U.S. President Barack Obama may have won over voters in the 2008 election using “a covert form of hypnosis” pioneered by an American doctor.