Purpose of This Module

The purpose of this module is to ensure an understanding of terms and basic concepts related to HIV and AIDS.

Defining Our Terms

Throughout this course, we often refer to “HIV/AIDS” when talking about issues that relate both to infection with HIV and the progression of the infection to AIDS. However, it is important to understand the difference between the two.

HIV infection

HIV is a member of a group of viruses called retroviruses. A retrovirus is a virus that changes itself very rapidly. One reason why HIV is a particularly serious infection is that it attacks and destroys cells of the immune system—called T-cells or CD4 cells—that are designed to fight infections and diseases. After HIV penetrates these cells, it takes over their machinery (or reprograms the cell) so that it begins to produce many copies of the virus. Eventually, HIV destroys the immune cells. Another reason why HIV is a very serious infection is that it has the ability to mutate (change itself) rapidly. This makes it especially difficult for researchers to find an effective treatment or vaccine.

There are two types of HIV. HIV-1 is responsible for the vast majority of infection and cases of AIDS in the world. HIV-2 is the more common type in West Africa and has a slower course than HIV-1.

From the time a person is infected with HIV, the virus begins to damage the immune system. Although an infected person’s immune system struggles to fight back—and can do so for as many as 10 years or more in an otherwise healthy adult—the virus continues to destroy these defenses until the immune system is too weak to fight off infections. 

A person can be infected with HIV and not know it, because any symptoms or illnesses related to HIV may not occur for many years after infection. Most people lead healthy and productive lives after HIV infection—in fact, many people are not aware they are infected because they feel fine. Unfortunately, even if the infected person feels fine, he or she can pass the infection on to others.

AIDS

AIDS is advanced HIV infection—it is the late stage of the infection, when the immune system is weakened. Advanced infection with HIV weakens the immune system to the point that it cannot fight off infections as effectively as usual. The individual becomes more susceptible to a variety of infections (called opportunistic infections) and other conditions (e.g., cancer). Eventually, the infected person may lose weight and become ill with such diseases as persistent severe diarrhea, fever, tuberculosis, pneumonia, or skin cancer. Opportunistic infections are known as such because they take advantage of a weakened immune system to cause illness. Some examples of opportunistic infections include chronic cryptosporida diarrhea, cytomegalovirus eye infection, mycobacterium avium complex, pneumocystis pneumonia, and toxoplasmosis. Other AIDS-associated conditions include invasive cervical cancer, Kaposi’s sarcoma, and lymphoma.

According to the U.S. Centers for Disease Control and Prevention, any one of a number of conditions indicating severe immunosuppression, or HIV infection in an individual with a CD4 (T-cell) count less than 200 cells per microliter (less than half of what is considered to be the bottom of the normal range), constitutes an AIDS diagnosis.

Conditions included as
AIDS-defining illnesses

Persons living with AIDS often have multiple infections, neurological disorders, extreme weight loss, diarrhea, and cancers. Although an infected person generally dies as a result of complications of these infections, conditions, and malignancies, living with AIDS is like living with other chronic diseases: sometimes the person feels sick, and at other times he or she feels fine and can go about normal activities.

No one dies from AIDS or HIV; rather, a person with AIDS dies from an infection or condition that his or her weakened immune system can no longer fight off.

In the U.S. and Europe, the average time from HIV infection to the development of AIDS is more than 11 years. In developing countries, the average time is shorter, which is probably due to multiple factors, including a higher background level of pre-existing infections; less access to care, including prophylaxis for opportunistic infections; and poor nutrition. Progress of the infection in infants is generally much faster than in adults.

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