Doctors believe that AIDS develops when a microscopic particle—a virus called HIV (Human Immunodeficiency Virus)—invades the bloodstream. Once there, the virus embarks on a seek-and-destroy mission against certain of the body’s white blood cells, the helper T cells. These cells play a major role in helping the body ward off disease. The AIDS virus, however, disables them, devastating the immune system.

Considerable time may pass before the infected one feels sick. Some may be symptom free for nearly a decade. But in time flu-like symptoms develop—loss of weight and appetite, fever, and diarrhea. As the immune system continues its catastrophic collapse, the victim becomes vulnerable to a host of infections—pneumonia, meningitis, tuberculosis, or certain cancers—called opportunistic because they make use of the opportunity created by a victim’s lowered resistance.

What makes the AIDS virus so deadly is the fact that it attacks and disables key cells, including white blood cells that the body produces to help ward off disease. These white blood cells (called T-4 lymphocytes) are the body’s main defense against disease.

When these white cells are disabled by the AIDS virus, they cannot do their job. Thus, the body’s immune system is devastated. Infections that may not previously have been life-threatening now are. These include other viruses, parasites, bacteria, fungi, or various cancers.

Since the body is no longer able to fight these infections, they progress until the victim is dead. These infections are called opportunistic. They take advantage of the opportunity afforded to them by the body’s suppressed immune system. A person with AIDS may have several such infections at the same time.

Among the early symptoms of AIDS are: prolonged and unexplained fatigue; swollen glands that last for months; persistent fevers or night sweats; persistent diarrhea; unexplained weight loss; discolored lesions of the skin or mucous membranes that do not go away; a persistent, unexplained cough; a thick whitish coating on the tongue or in the throat; easy bruising or unexplained bleeding. These early symptoms are often referred to as “AIDS Related Complex,” or ARC.

When AIDS becomes full-blown, deadly diseases develop. Among the more common are lung infections caused by parasitic germs known as Pneumocystis carinii, and the skin cancer called Kaposi’s sarcoma, which also involves internal organs. In addition, the AIDS virus can affect the brain, causing paralysis, blindness, dementia, and eventual death. Dr. Richard T. Johnson, a Johns Hopkins professor of neurology, stated: “HIV [the AIDS virus] is in the brains of at least 1 million people in the U.S.”

Full-blown AIDS is accompanied by pain and uncontrollable weight loss, with the body getting weaker and weaker until death ensues. In Africa, says The Lancet, AIDS “has been associated with ‘slim disease,’ a term that describes the great loss of weight that accompanies diarrhea.” From the onset of the disease to death may take a year or less, or it may take several years.

There is another factor that contributes to making the AIDS virus more deadly than others. It has built-in mechanisms for survival not common to other viruses.

For example, in humans the influenza virus may last only a few days or weeks, and it stimulates antibodies that help to protect the victim from further infection by that particular virus. Once the epidemic runs its course, it disappears. The flu pandemic of 1918 lasted only about a year. The yellow fever virus depends on mosquitoes, which diminish in number with seasonal changes. Smallpox may also quickly run through a susceptible population and then disappear.

However, the AIDS virus is presumed to be persistent. It probably stays inside the human host for a lifetime and does not disappear on its own. The victim does not recover from the full-blown AIDS disease and so is unable to build the kind of immunity that would resist a recurrence.

Furthermore, the AIDS virus has shown significant variation in its genetic composition, making it more difficult to develop a vaccine. And viruses usually mutate, that is, change their character. For example, there are many different types of influenza and cold viruses. Already, a second type of AIDS virus has been identified in Africa and elsewhere. A different vaccine may be required for each type.