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How? Aids Spread
HIV is a lentivirus, and like all other viruses of
this type, it too attacks the immune system of the infected.
Lentiviruses are in turn a part of another larger group of viruses
known as retroviruses. The name 'lentivirus' literally means 'slow
virus' because they take very long time to generate any unpleasant &
adverse effects in the body. They have been found in a number of
different animals, including cats, sheep, horses and cattle however,
the most interesting lentivirus in terms of the investigation into
the origins of HIV is the Simian Immunodeficiency Virus (SIV) that
affects monkeys.
It is now generally accepted that HIV is a
descendant of a Simian Immunodeficiency Virus because certain
strains of SIVs bear a very strong resemblance to HIV-1 and HIV-2,
the two types of HIV. HIV-2 for example corresponds to SIVsm, a
strain of the Simian Immunodeficiency Virus found in the sooty
mangabey (also known as the green monkey), which is indigenous to
western Africa. The more virulent strain of HIV, namely HIV-1, was
until recently more difficult to place since till 1999, the closest
counterpart that had been identified was SIVcpz, the SIV found in
chimpanzees however, this virus still had certain noteworthy
differences from HIV.
In February 1999 a group of researchers from the
University of Alabama1 announced that they had found a type of
SIVcpz that was almost identical to HIV-1. This particular strain
was identified in a frozen sample taken from a sub-group of
chimpanzees known as Pan troglodytes troglodytes, which were once
common in west-central Africa. The researchers lead by Paul Sharp of
Nottingham University and Beatrice Hahn of the University of Alabama
made the discovery and claimed that this sample proved that
chimpanzees were the source of HIV-1, and that the virus had at some
point crossed species from chimps to humans, during the course of a
10-year long study into the origins of the virus.
Their final findings were published two years later
in Nature magazine the article in which, they concluded that wild
chimps had been infected simultaneously with two different simian
immunodeficiency viruses which had "viral sex" to form a third virus
that could be passed on to other chimps and, more significantly, was
capable of infecting humans and causing AIDS. These two different
viruses were traced back to a SIV that infected red-capped mangabeys
and one found in greater spot-nosed monkeys. They believe that the
hybridisation took place inside chimps that had become infected with
both strains of SIV after they hunted and killed the two smaller
species of monkey.
It has been known for a long time that certain
viruses can pass between species. Indeed, the very fact that
chimpanzees obtained SIV from two other species of ape shows just
how easily this crossover can occur. As animals ourselves, we are
just as susceptible. When a viral transfer between animals and
humans takes place, it is known as zoonosis. Below are some of the
most common theories about how this 'zoonosis' took place, and how
SIV became HIV in humans:
The most commonly accepted theory is that of the
'hunter'. In this scenario, SIVcpz was transferred to humans as a
result of chimps being killed and eaten or their blood getting into
cuts or wounds on the hunter. Normally the hunter's body would have
fought off SIV, but on a few occasions it adapted itself within its
new human host and become 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
man, it would have developed in a slightly different way within his
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 to ten (1%) were
infected with SFV (Simian Foamy Virus), an illness which, like SIV,
was previously thought only to infect primates. All these infections
were believed to have been acquired through the butchering and
consumption of monkey and ape meat. Discoveries such as this have
lead to calls for an outright ban on bush meat hunting to prevent
simian viruses being passed to humans.
Some other rather controversial theories have contended that HIV was
transferred iatrogenically (i.e. via medical experiments). One
particularly well-publicized idea is that polio vaccines played a
role in the transfer. In his book, The River, the journalist Edward
Hooper suggested that HIV could be traced to the testing of an oral
polio vaccine called Chat, given to about a million people in the
Belgian Congo , Ruanda and Urundi in the late 1950s. To be
reproduced, live polio vaccine needs to be cultivated in living
tissue, and Hooper's belief is that Chat was grown in kidney cells
taken from local chimps infected with SIVcmz. This, he claims, would
have resulted in the contamination of the vaccine with chimp SIV,
and a large number of people subsequently becoming infected with
HIV-1. However, in February 2000 the Wistar Institute in
Philadelphia (one of the original places that developed the Chat
vaccine) announced that it had discovered in its stores a phial of
polio vaccine that had been used as part of the program. The vaccine
was subsequently analyzed and in April 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. While
this is just one phial of many, most have taken its existence to
mean that the OPV vaccine theory is not possible. The fact that the
OPV theory accounts for just one (group M) of several different
groups of HIV also suggests that transferal must have happened in
other ways too. The final element that suggests that the OPV theory
is not credible as the sole method of transmission is the argument
that HIV existed in humans before the vaccine trials were ever
carried out. More about when HIV came into being can be found below.
This is an extension of the original 'hunter' 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 healthcare professionals working on inoculation and other
medical programmes, the huge quantities of syringes needed would
have been very costly. It is therefore likely that one single
syringe would have been used to inject multiple patients without any
sterilisation in between. This would rapidly have transferred any
viral particles (within a hunter's blood for example) from one
person to another, creating huge potential for the virus to mutate
and replicate in each new individual it entered, even if the SIV
within the original person infected had not yet converted to HIV. The colonialism or 'Heart of Darkness' theory, is one of the more
recent theories to have entered into the debate. It is again based
on the basic 'hunter' premise, but more thoroughly explains how this
original infection could have lead to an epidemic. It was first
proposed in 2000 by Jim Moore, an American specialist in primate
behaviour, who published his findings in the journal AIDS Research
and Human Retroviruses. During the late 19th and early 20 th
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 labour camps
where sanitation was poor, food was scare 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
labour force and taken advantage of their weakened immune systems to
become HIV. A stray and perhaps sick chimpanzee with SIV would have
made a welcome extra source of food for the workers. Moore also
believes that many of the labourers would have been inoculated with
unsterile 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 labourers
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 labour camps
were set up around the time that HIV was first believed to have
passed into humans - the early part of the 20th century. Some say that HIV is a 'conspiracy theory' or that it is 'man-made'.
A recent survey carried out in the US for example, identified a
significant number of African Americans who believe HIV was
manufactured as part of a biological warfare programme, designed to
wipe out large numbers of black and homosexual people. Many say this
was done under the auspices of the US federal 'Special Cancer Virus
Program' (SCVP), possibly with the help of the CIA. Some even
believe that the virus was spread (either deliberately or
inadvertently) to thousands of people all over the world through the
smallpox inoculation programme, or to gay men through Hepatitis B
vaccine trials. While none of these theories can be definitively
disproved, the evidence they are based on is tenuous at best, and
often ignores the clear link between SIV and HIV, or the fact that
the virus has been identified in people as far back as 1959. They
also fail to take into consideration the lack of genetic-engineering
technology available to 'create' the virus at the time that AIDS
first appeared. |
