Thursday, February 25, 2010

The origin of HIV and AIDS

For over twenty years it has been a cause of countless arguments, with everything from a promiscuous flight attendant to a suspect vaccine program being blamed. What is the truth?

The first recognized cases of AIDS occurred in the USA in the early 1980s. A number of gay men in New York and California suddenly began to develop rare opportunistic infections and cancers that seemed stubbornly resistant to any treatment. At this time, AIDS did not yet have a name, but it quickly became obvious that all the men were suffering from a common syndrome.

What type of virus is HIV?

HIV is a lentivirus which attacks the immune system. The name 'lentivirus' literally means 'slow virus' because they takes heck of a long time to manifest as a disease. They have been found in a number of different animals, including cats, sheep, horses and cattle. But the most interesting lentivirus in terms of its relation to HIV is the Simian Immunodeficiency Virus (SIV).

So did HIV come from Chimps?

It is now generally accepted that HIV is a descendant of a SIV because certain strains of SIVs bear a very close resemblance to HIV-1 and HIV-2.

HIV-2 for example corresponds to SIVsm, a strain of the SIV found in the sooty mangabey (White-collared monkey)-indigenous to western Africa. Other closest counterpart of HIV that had been identified was SIVcpz-found in chimpanzees.

Scientists now believe that chimpanzees were the source of HIV-1, and that the virus had at some point crossed species from chimps to humans. It was then concluded that all three 'groups' of HIV-1 - namely Group M, N and O came from the SIV found in this particular Chimp (P. t. troglodytes), and that each group represented a separate crossover 'event' from chimps to humans.

How could HIV have crossed species?

It has been known for a long time that certain viruses can pass between species. As animals ourselves, we are just as susceptible. There are various theories about how this 'zoonosis' took place, and how SIV became HIV in humans:

The 'Hunter' Theory

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. Initially the body would have fought off SIV, with time it adapted itself within 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, would support this theory as 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.

The Oral Polio Vaccine (OPV) theory

Some other rather controversial theories have contended that HIV was transferred iatrogenically. One particularly well-publicized idea is that polio vaccines played a role in the transfer.

An oral polio vaccine called “Chat” was tested on about a million people in the Belgian Congo, Ruanda and Urundi in the late 1950s. This theory suggests that “chat” was grown in kidney cells taken from infected chimps. This would have resulted in the contamination of the vaccine with chimp's SIV, and a large number of people subsequently becoming infected with HIV-1.

People have contested saying that local chimps were not infected with a strain of SIVcpz that is closely linked to HIV. Furthermore, the oral administration of the vaccine would seem insufficient to cause infection in most people as virus needs to get directly into the bloodstream to cause infection.

Later, Wistar Institute in Philadelphia (one of the original manufacturers of the Chat vaccine) announced the vaccine was analyzed and no trace had been found of either HIV or chimpanzee SIV.

The Contaminated Needle Theory

Even though the use of disposable plastic syringes became common around the world in 1950s, some parts of Africa might not have done so. It is therefore 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, allowing virus to mutate and replicate.

The Colonialism Theory

During the colonial rule Africans were forced into labour camps with poor sanitation, scare food supply and physical demands were extreme. Prostitution was widespread and workers would have been treated with poor health ethics including non sterile needles. 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.

The Conspiracy Theory

A a significant number of African Americans believe HIV was manufactured as part of a biological warfare program, 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. Spread through smallpox inoculation programme, or to gay men through Hepatitis B vaccine trials.