Where did HIV originate? How did the disease jump from non-human primates to humans? How is it spread through the human population today?
Where did HIV originate?
The answer to the question of where Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome originated has been elusive. Many different explanations concerning its emergence and its cause have been debated within the scientific community. Only recently has it been accepted widely that HIV is a descendant of a Simian Immunodeficiency Virus (SIV), The acceptance that HIV came from SIV is due to the fact that certain strains of SIV share very similar genetic make-ups to HIV-1 and HIV-2 which are two types of HIV.
HIV-1, which is the more virulent strain of HIV, shows a very close resemblance to a strain of SIV called SIVcpz and is found in chimpanzees.
HIV-2 shows a correspondence with an SIV that is found in the sooty mangabey, an animal indigenous to western Africa.
With the very close relationships seen between SIV strains and the two HIV strains, it is believed that the HIV strains had descended from the SIV and had adapted to using humans as a host.
How did the disease jump from non-human primates to humans?
Several theories have been presented to explain the transfer of the disease from animals to humans, also known as zoonosis. These theories include the Hunter theory, the Oral Polio Vaccine theory, Conspiracy, and several other theories that play off the Hunter theory but with different scenarios.
The Hunter theory is the most accepted theory as to how HIV crossed species. It is assumed that SIVcpz, that causes HIV-1, was transferred to humans through the result of chimps being killed and eaten by hunters. The hunters may have also gotten the virus by having blood from the chimpanzees getting into cuts or wounds on the hunter. This theory is supported by the idea that as the virus was introduced to the new human host, it would evolve slightly to allow it to infect the hunter. Each new hunter infected would produce a slightly different strain of HIV-1 which can be seen in the multiple subtypes present in HIV-1. From there, any sexual contact between the infected hunter and another human could then pass the virus on to others. This is the most common belief because many tribes in Africa hunt chimps and it has been shown that they contain many viruses. The fact that they contain these viruses has led some countries to ban the hunting of chimps.
Oral Polio Vaccine
A lesser accepted theory about the crossing of the virus from primates to humans is the Oral Polio Vaccine Theory. It is thought that a polio vaccine was responsible for the spread of HIV through medical interventions. The vaccine needed to be made in living tissue and it was believed that the tissue used were kidney cells from chimpanzees that were infected with an SIV. This supposedly contaminated the vaccines with the virus and around 1 million people in Belgian Congo, Rwanda, and Urundi may have become infected with HIV-1 causing those who took the vaccine to become infected. However, this theory has been refuted by many scientists because an oral vaccine would appear not to be efficient in causing viral infection due to the fact that the virus needs to get directly into the bloodstream and the lining of the mouth and throat usually act as good barriers to viruses. Recently, it was also discovered that the kidney cells were from macaque monkeys and they cannot be infected with the virus. Since this information was found from only a few of the actual samples used, there may be a possibility that macaque monkeys were not the only primates used for kidney cells, thus leaving this theory still possible. It must be noted, however, that due to lack of convincing evidence, this theory is not likely to be the cause of human infection with HIV.
One theory that circulated for some time and that has been scientifically disproven is the Conspiracy Theory. Some believed that HIV is a human-made virus, developed as part of a biological warfare program to rid the world of black and homosexual people. They also believed that it was spread through smallpox inoculations, and to gay men through Hepatitis B vaccine trials. Such theorists do not take into account the that HIV has a clear link to SIVs and that HIV had been reported in people before the inoculation or vaccine trials were even distributed. There has also been documentation that the technology needed to create such a virus was not possible at the time that HIV started infecting humans. This makes it obvious that the Conspiracy Theory is just not possible.
With several theories as to how HIV-1 crossed to humans, how did HIV-2 cross species? The emergence of HIV-2 in humans is believed to have happened in a fashion that resembles the Hunter theory, involving the butchering and consumption of sooty mangabey meat. Since the infection by HIV-2 is less frequently seen, and is much less virulent than HIV-1, it infects far fewer people and has mostly stayed in a small number of countries in West Africa.
How is HIV spread through the human population today?
As with any virus, once it establishes itself in a host, the virus needs a way to transfer itself from one host to another. HIV is no different. HIV can be transmitted from human to human in ways that include: sexual intercourse, mother-to-child transmission, injection drug use, and other types of contact with infected blood. Sexual intercourse is the most common way for HIV to be spread and it is usually the result of unprotected sexual relations. Transmission through sex occurs when an infected partner transmits the virus to another partner through sexual secretions and it comes into contact with genital, oral, or rectal membranes of the non-infected partner. Though the Catholic Church does not approve of the use of condoms, the risk of sexual transmission can be significantly reduced with the proper use of a condom. The chance can be reduced to 0% by abstaining entirely from sex.
Another way that HIV is transferred is by mother-to-child transmission. It can occur in utero during pregnancy and intrapartum at child birth. Even after the child is born, there is a possibility that mother-to-child transmission can occur. This risk is present in the practice of breast feeding. As the child feeds on the mother’s milk, the virus may be transmitted and therefore infecting the child as well.
A third way that humans have managed to transfer the virus is through injection needle use. Needle sharing is the main cause for this type of transmission and it occurs when one infected individual uses the needle to inject drugs into their bloodstream and upon injection the needle becomes contaminated with the virus. Another individual then used the same needle to inject drugs and they are then infected.
Sometimes transmission occurs by blood or blood product transfusions. Those receiving transfusions are given blood that is infected with HIV and they too become infected. This type of transmission is very rare in developed countries on account of tests that are conducted to make sure that recipients of blood transfusions are receiving blood that is not contaminated in any way.
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