HIV is different from most viruses. If you get a flu virus, you may get symptoms right away. Many people infected with HIV may not have clear symptoms of HIV infection for many years. That is because of the unique way that the virus works in the body.

HIV enters macrophages (a type of cell found in many parts of the body), which act as host cells for the virus. Instead of rupturing its host cells right away, as most viruses do, HIV multiplies quietly in the macrophages for years. During this time, HIV copies itself within these host cells, exits the macrophages without damaging them, and then enters other  macrophages. While this is happening, the virus is doing no apparent damage to the body, and the person with HIV is symptom-free. Eventually, HIV begins infecting a type of cell called CD4 positive T cells (abbreviated as CD4+ T cells). These are the white blood cells that lead the attack against infections. Instead of quietly multiplying as it did in macrophages, HIV replicates (or copies itself) in CD4+ T cells and then ruptures and destroys these host  cells. As more and more HIV is produced, more and more CD4+ T cells are destroyed, and the body’s defenses are weakened.

HIV presents a huge challenge to the immune system. Because it destroys the body’s T cells, it makes it difficult—if not impossible—for the immune system to fight off disease-producing organisms. This is where opportunistic infections come in. Although they usually can be fought off by a healthy immune system quite easily, opportunistic infections can cause terrible illness in someone infected with HIV. The following paragraphs show the several stages of illness that occur as the action of the virus progresses:

The first symptoms can appear two to four weeks after exposure to the virus. Often, these symptoms are similar to those associated with the flu or with mononucleosis (“mono”). Even if the symptoms  appear early, an actual diagnosis might not be possible for months. This is because someone with the symptoms of HIV infection will not be HIV positive by certain lab tests for three months or even as long as a year. It is vitally important to know, however, that, at this stage of the illness, the virus can be transmitted. Over time, acute HIV infection advances to “asymptomatic” HIV infection.

In this stage, the person is without symptoms (or “asymptomatic”). The length of the symptom-free period varies. It can last for just a few years, or it can extend to 10 years or longer. During this stage, those infected are still highly contagious. How long the stage lasts depends on how much HIV has replicated in the body. Because the virus lives in white blood cells, it spreads best when the body “turns on” the immune system. Staying healthy will keep the virus from spreading throughout the body. The amount of time this symptom-free stage lasts also depends on how well the person’s immune system deals with the virus. During this period, the virus still is infecting and killing T cells. From the symptom-free stage, the condition often progresses to early symptomatic HIV infection, also called AIDSrelated complex (ARC).

During this stage of the condition, symptoms appear, including fevers, swollen glands, and thrush; the ARC stage is just before the development of AIDS. People at the ARC stage are infected and therefore are HIV antibody positive. The ARC period is really the transition from HIV infection to HIV disease. The person with HIV has not yet developed opportunistic infections, cancers, or AIDS. Finally, though, early symptomatic HIV infection develops into AIDS.

This is the final and most deadly stage of HIV disease. A person is said to have AIDS when he or she has fewer than 200 CD4+ T cells per cubic millimeter of blood. (Healthy adults have a CD4+ T-cell count of 1,000 or more.) Remember, CD4+ T cells are the primary host cells of HIV. When HIV destroys these cells, it makes the immune system weaker and allows opportunistic infections to develop. During this stage, an HIV-infected person often suffers from many opportunistic infections. These infections can attack the brain, the lungs, and other organs and can be caused by viruses, bacteria, or parasites or by cancer cell growth.

Although most people with HIV end up getting AIDS, some people infected with HIV will develop AIDS either very slowly or not at all. These people are called non-progressors. In some cases, non-progressors who have tested positive for HIV in the past eventually test negative and then show no signs of infection. These people are being carefully monitored, because monitoring them might show that the body is capable of controlling the virus. For the vast majority of HIVinfected people, however, the virus will progress to AIDS.