Origins Of HIV-AIDS

Theories about the origin of the AIDS epidemic have been plentiful ever since doctors first noticed the disease, in five gay men in Los Angeles in 1981. Some were entirely unscientific: most famously, God was punishing homosexuals. Others were grounded to various degrees in science: A contaminated hepatitis B vaccine tested in gay men was to blame. A campaign by the World Health Organization to eradicate smallpox had somehow awakened dormant HIVs that had long infected human beings harmlessly. The CIA had concocted the virus in a lab, or it came from space, or from a distantly related cow virus that had contaminated all sorts of vaccines. Scientific research in the field of epidemiology would eventually pick through the various speculations, accusations, and rumors, leaving us with a more defined path of origin of HIV-AIDS today.

It is now generally accepted that HIV is a descendant of a Simian Immunodeficiency Virus (SIV) because certain strains of SIV's have a very close resemblance to HIV-1 and HIV-2, the two types of HIV. HIV-2 corresponds to a strain of SIV found in the sooty mangabey (also known as the White-collared monkey), which is indigenous to western Africa. The more virulent, pandemic strain of HIV, HIV-1, was not directly linked with a strain of SIV until 1993, when two seperate SIV infections of wild common Chimpanzees from Gabon were confirmed by researchers at the International Center for Medical Research of Franceville, in the country of Gabon, West Africa.

In 1999 researchers from the University of Alabama announced that they had found a type of SIVcpz that was almost identical to HIV-1. In their article, published in a 2001 edition of the journal Nature, they concluded that wild common Chimpanzees had been infected simultaneously with two SIV's which hybridized to form a third unique virus. This virus could be passed on to other chimps, and was capable of infecting humans, a process called zoonotic transfer. They believed that the hybridization took place inside chimps that had become infected with both strains of SIV after they hunted and killed two smaller species of monkey. They also concluded that all three subgroups of HIV-1 - group M, N and O - came from the SIVcpz found in the common Chimpanzee (reaffirming the evidence from 1993), and that each group represented a separate crossover event from chimps to humans.

Below are some of the more plausible theories about how this zoonosis took place, and how SIV became HIV in humans:

Hunter Theory

In this scenario, SIV was transferred to humans as a result of primates being killed and eaten or their blood getting into cuts or wounds on bushmeat hunters . Normally the human recipients immune system would have fought off SIV, but on a few occasions it adapted itself within its new human host and became HIV-1. The fact that there were several different early strains of HIV, each with a slightly different genetic make-up (the most common of which was HIV-1 group M), would support this theory: every time it passed from a chimpanzee to a human, it would have developed in a slightly different way within his/her body, and thus produced a slightly different strain. An article published in The Lancet in 2004, also shows how retroviral transfer from primates to hunters is still occurring even today. In a sample of 1099 individuals in Cameroon , they discovered ten (1%) were infected with Simian Foamy Virus (SFV), an illness which was previously thought only to infect primates. All these infections were believed to have been acquired through the butchering and consumption of primate bushmeat. A growing number of epidemiologists are now calling for an outright ban on bushmeat hunting to prevent the spread of simian viruses to humans.

Oral Polio Vaccine (OPV) theory

Some other rather controversial theories have contended that HIV was transferred iatrogenically (via medical interventions). One particularly well-publicized idea is that polio vaccines played a role in the transfer. In the book "The River", by Edward Hooper, it is suggested that HIV can be traced to the testing of an oral polio vaccine called Chat, given to approximately one million people in the Belgian Congo, Ruanda and Urundi in the late 1950's. To be reproduced, live polio vaccine needed to be cultivated in living tissue, and Hooper's belief is that Chat was grown in kidney cells taken from local Chimpanzees infected with SIVcpz. This, he claims, would have resulted in the contamination of the vaccine with Chimpanzee SIV, with a large number of people subsequently becoming infected with HIV-1. Some facts contest Hooper's theory: the oral administration of the vaccine would seem insufficient to cause infection in most people (the lining of the mouth and throat generally act as good barriers to the virus). In 2000 the Wistar Institute in Philadelphia (one of the original manufacturers of the Chat vaccine) discovered a vial of polio vaccine that had been used as part of the program. The vaccine was analyzed and in 2001 it was announced that no trace had been found of either HIV or chimpanzee SIV. A second analysis confirmed that only macaque monkey kidney cells, which cannot be infected with SIV or HIV, were used to make Chat. This does not necessarily disprove the OPV theory, as the discovery of a vial from one pool of many batches of the vaccine does not account for the total variance in a vaccination used by over 1 million people.

Contaminated Needle Theory

In the 1950s, the use of disposable plastic syringes became commonplace around the world as a cheap, sterile way to administer medicines. However, to African health care professionals working on inoculation programs, the huge quantities of syringes needed would have been very costly. It is therefore possible, if not likely, that one single syringe would have been used to inject multiple patients without any sterilization in between. This would rapidly have transferred any viral particles from one person to another, creating huge potential for the virus to mutate and replicate in each new individual it entered.

Colonialism Theory

The colonialism, or "Heart of Darkness" theory was first proposed in 2000 by Jim Moore, a primatologist who published his findings in the journal AIDS Research and Human Retroviruses. During the late 19th and early 20th century, much of Africa was ruled by colonial forces. In areas such as French Equatorial Africa and the Belgian Congo, colonial rule was particularly harsh and many Africans were forced into labor camps where sanitation was poor, food was scarce and physical demands were extreme. These factors alone would have been sufficient to create poor health in anyone, so SIV could easily have infiltrated the labor force and taken advantage of their weakened immune systems to become HIV. A stray and perhaps sick chimpanzee with SIV would have been an extra source of food for the workers to utilize in their survival. Moore also believes that many of the laborers would have been inoculated with unsterilized needles against diseases such as smallpox (to keep them alive and working), and that many of the camps actively employed prostitutes to keep the workers happy, creating numerous possibilities for onward transmission. A large number of laborers would have died before they even developed the first symptoms of AIDS, and those that did get sick would not have stood out as any different in an already disease-ridden population. Even if they had been identified, all evidence (including medical records) that the camps existed was destroyed to cover up the fact that a staggering 50% of the local population were wiped out there. One final factor Moore uses to support his theory, is the fact that the labor camps were set up around the time that HIV was first believed to have passed into humans - the early part of the 20th century.

To date, researchers have found SIV viruses in nearly two dozen primate species. If these viruses have repeatedly jumped from nonhuman primates to human beings through zoonotic transfer, there is the frightening possibility of new epidemics in waiting. Although the United States alone spends about $2 billion annually on AIDS research, the bulk of this amount rightly goes toward the search for better ways to prevent and treat HIV infections; perhaps $1 million is spent on investigations into the epidemic's origin. The few people who have committed themselves to the inquiry have done so at great risk, professionally and sometimes physically. Those who conduct research in Africa must deal with crumbling infrastructure that forces them to move at a maddeningly slow pace, must contend with the ever-present disruption and danger of civil war, and must hope to avoid a long list of infectious diseases, one of which recently took the life of a prominent biologist.

Using HIV-1 sequences preserved in human biological samples along with estimates of viral mutation rates, scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanization and colonization in equatorial Africa. Exactly when the zoonosis occurred is not known. Some estimates suggest that HIV-1 (group M) entered the human population in the early 20th century, probably between 1915 and 1941. A study published in 2008, analyzing viral sequences recovered from a recently-discovered 1960 biopsy along with previously-known sequences, suggested a common ancestor between 1884 and 1924.