>>c0nc0rdance: Where does HIV come from?
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.