For some of us who remember the sudden emergence of HIV into the popular culture and awareness

of the US in the early 1980's, HIV appears to have come from nowhere. Rumor swirled about

where it came from, how it came to infect people from all walks of life around the world.

It's only now, after over 25 years of research and discovery that we can finally start to

say with some confidence where HIV came from.

HIV is a lentivirus on the basis of its genome and life cycle. It's not all that unusual

for the lentiviruses. It infect immune cells, primarily CD4+ T cells and macrophages. The

other lentivirus pursue similar, if slightly different life cycles.

For example, the Simian Immunodeficiency Virus strain that infects African Green Monkeys

doesn't usually cause much disease to its host. The rhesus macaque also has a strain

of SIV that causes little or no disease. However, if you take a rhesus macaque, a monkey from

Asia... and infect it with the SIV from the African monkey, or if you infect the African

monkey with the Asian virus, the result is called Simian AIDS.

This observation led scientists to suspect that HIV has not been a human virus for very

long. If it was a virus with a lot of history with humans, it's unlikely it would still

be so pathogenic. Where could HIV have come from? We sequenced the genome of thousands

of strains of HIV, and while there was an incredible diversity of sequences at certain

locations, they all had a strong homology to various SIV strains.

We usually break up the strains of HIV into two main groups, the HIV-1 and HIV-2 species.

The closest relative, according to sequence variations, for the HIV-1 strain was the SIV

that infects chimpanzees. The closest relative of HIV-2, a viral species largely found in

Africa, appears to the be the SIV found in sootey mangabeys.

Africa possesses far more of the subgroupings of HIV than any other continent. Europe and

North America are dominated by a very narrow range of viral types, the Group M, subtype

B. This is suggestive, but not confirmatory, of an African origin for the parent strains.

We know that SIV and HIV are both spread in the same ways, sex and blood transfers. Blood-to-blood

exposures, however, are 900 times more likely to result in infection than sex contact. It

is therefore likely that the transmission from primate to human, called a zoonotic event,

was the result of hunters trapping, butchering, and eating chimps. The practice of hunting

primates for what is called bushmeat is well documented in tribal groups in certain areas.

So we have a strong suggestion of where to look: African monkeys. In fact, evidence of

viral evolution suggested a certain region of Western equatorial Africa. It was here

that a colony of chimpanzees were found with a close relative of the ancestral strain of

HIV-1. Based on mutation and divergence rates, we can place at least one transfer of virus

from chimp to human at or around 1931 in the country now known as the Democractic Republic

of Congo. There is some evidence to suggest that previous transfers of chimp to human

may have occurred as far back as the 1880's, but it's not yet clear if these transfers.

The first clear case of verified infection in a human sample was in the 1960's, so the

initial expansion was probably in the mid to late 50's.

What was going on in the 1950's in Africa? Urbanization, for one.

The cities of equatorial Africa experienced a population boom after World War 2 along

with colonial expansion. The world wanted the raw resources in Africa, and needed local

labor to extract it. This led to a disruption of traditional lifestyles, and the rise of

a post-industrial culture in a previously agrarian society. Prostitution and drug use

may have increased as people left their towns and villages to find profitable work in the

growing cities. They probably left their families and communities behind, and many were no doubt

lonely and isolated in this new cultural setting. It could be said that it was not African culture

that led to the spread of HIV, but the effect of colonialim and industrialization in an

area that has frequent contact with our close primate relatives.

Previous zoonotic transfers of HIV, and it's likely that there were many over the centuries,

from prey to hunter, were previously isolated by the low infection rate for anything but

blood-blood contact. It was the addition of injectable drugs, prostitution, and urbanization

that probably allowed HIV to escape the small region in which it fequently emerged.

It appears that the next link in the chain was either to Haiti by direct immigration

or directly to the US, or it might have been spread to Europe by sailors on cargo ships

and then to North America. The data is a bit spotty, but the emergence in the major cities

of Europe was slightly after the disease was documented in New York and San Francisco.

Asia and Russia may have been infected by a second wave of emergence, as their subtype

profiles are markedly different than the European and North American subtypes. South America,

Australia, and Northwest Asia are a possible third wave emergence.

The popularized idea of the Canadian flight attendant as patient zero is very misleading.

He was certainly not the first case outside of Africa, or in North America, but he was

the index case in a large cluster of 248 patients in 1983.

The other origin rumors that are very prevalent are the man-made pandemic theories. For example,

the oral poliovirus vaccine transmission theory, which has no basis in fact, but it satisfies

the need some people have for a good narrative with a shadowy, evil agency acting behind

the scenes.

The OPV hypothesis, advanced by BBC correspondent Edward Hooper, and documented in his book,

The River, suggests that an SIV-contaminated chimpanzee culture was used to prepare the

oral poliovaccine given in the late 50's and early 60's. His theory, which was effective

at selling his book, and ignited the imagination of conspiracy theorists, proposed that this

SIV contaminated vaccine culture humanized the simian virus. But, as the evidence shows,

HIV had emerged in it's modern form prior to the polio vaccine era. The frozen vaccine

lots of that time period were thawed and tested for the presence of either SIV or HIV by an

impartial third party.

It is also completely implausible that HIV is an engineered virus or bioterror agent.

The state of molecular biology in the 1950's was rudimentary. The capability did not exist

at the time to make the precise molecular changes needed to generate HIV from SIV. Even

crude techniques like coculturing of the simian virus with known human pathogens like influenza

would have been unsuccessful. HIV shows all the hallmarks of a zoonotic jump, not design.

I hope this has been informative. There's one concluding thought I'd like to leave you

with. There's so much information on the Internet which isn't based in fact, may be medically

dangerous, or based on a paranoid fantasy. Here's a general rule, call it C0nc0rdance's

rule: "Never take medical advice from the Internet". Ask a licensed, qualified doctor

what the best plan is for your health. Discuss with him or her any concerns you may have,

and radical life changes you want to try. Listen to their advice. Your local doctor

can help you sort the facts from the fiction, and keep you from doing harm to yourself or

others. Do it for the people you love and do it for yourself.

Thanks for watching.