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The Story of Evolution, Spring 2005
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Evolution of AIDS

Kelsey Smith

In "Darwin's Dangerous Idea", Dennett states that a meme is the name for any item of cultural evolution (342)." It can also be loosely defined as "idea." As it is passed from one person to another, its characteristics continue to change so its essence is not sacred. It is impossible to predict what form it will take as it continues to change because it can be influenced by a variety of factors in relation to the individual. As a consequence, the only constant factor in the process is the propensity for change. One example that is analogous to the changing nature of memes it the evolution of the AIDS virus.

When and antigen–-such as a virus--invades a human host, the immune system works to destroy it. Some white blood cells–macrophages–serve to maintain immunity to foreign organisms in a process known as phagocytosis, a word that means "cell eating." Another role that macrophages play is that they attach to invaders and send them to be annihilated by other parts of the immune system. The lymphocytes are specialized white blood cells that identify and destroy invading viruses. Some of them, B-cells, produce antibodies that circulate through the body and inactivate antigens by binding to them. Another type of lymphocyte, T-cells, carry out the job of destroying cells that are marked with antibodies.

The HIV virus disrupts the immune system response by interfering with the T-cells. This allows the virus to replicate rapidly. It invades a T-cell and uses it as a place to reproduce. Ultimately, the cell becomes filled with HIV cells and it explodes, allowing the new virus cells to infect other cells. Though the B-cells initially identify the virus as "foreign" and the macrophages consume the virus cells, these components of the immune system ultimately lose the battle. When a person has a T-cell count that is below 300, that individual is considered to have AIDS. At this point, a person is incapable of fighting off a myriad of opportunistic infections that would not be a problem if encountered by a person with a normal immune system.

Meanwhile, the AIDS virus is continuing to multiply. As it does so, it makes mistakes and the characteristics of the virus change slightly, much in the same way as memes change as they pass from person to person. As a consequence, the virus cannot be identified by the antibodies that the B-cells have produced. Another consequence of the virus continually changing is that it is impossible to wipe it out with a vaccine.

Sometimes, some of the AIDS virus cells will refrain from reproducing. Instead, they will enter T-cells and remain inactive for a while before choosing to multiply. They can remain in this state for several years, during which they are not detected by B-cells or consumed by macrophages. This is another hindrance to eradicating the virus because though some of the virus cells may not be evolving, the fact that they remain inactive is an effective evolutionary strategy that allows them to concurrently stay alive and stay undetected.

Though AIDS is incurable, it can be treated with drugs to boost the immune system and allow patients to live longer. Currently, there are four classes of drugs that can be used against AIDS and the most effective treatment uses multiple drug types. Over time, the virus evolves and in the process, develops resistace to drugs. This process is inevitable, but it necessitates the use of different drugs for treatment and it occurs more quickly if a person neglects to take all doses of the drugs. This resistance is transmitted when new individuals are infected. In fall of 2004, a man in New York City was infected with a strain of HIV that developed into AIDS in four months. Normally, HIV takes ten or more years to progress to AIDS, but this one develops into AIDS in two to twenty months. It is also resistant to three of the four classes of drugs, so there is not much that can be done for the man.

The process of developing new drugs is lengthy and involves four phases. Phase I involves testing the side effects of a drug on a population of healthy individuals to discover the side effects of different dosages of the drug. The trials usually involve less than 100 people and are over within a year. At this point, phase II occurs, testing the drug against an infected person to collect more information about side effects and to see how the drug works against the disease. Several hundred participant are divided into two equal groups: the first is given the drug, the second–known as the control–is given normal treatment. Under normal circumstances, it is unknown to both the doctors and the patients about what option each individual receives. In this method of conducting a blinded study, doctors can be completely objective when they examine the patients. Phase three is a larger sample–often more than a thousand people–and can take one to two years. It continues to evaluate the side effects and effectiveness of a drug. With good results in this phase, the drug can be marketed. Sometimes, phase IV can occur to evaluate the drug's long-term effectiveness and side effects. It can also compare the new drug to others approved for the same condition.

Basic AIDS Information:

Detection of a New Strain: 240060c.html

Phases of Drug Trials:

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