Human immunodeficiency virus (HIV) infects the cells of the immune system. In particular, HIV attacks and destroys the T helper lymphocytes, or T-cells, which are crucial to the immune system and immune response. (These cells are also called CD4-positive lymphocytes because HIV uses the protein CD4, present on the surface of the cell, to attach itself and pry its way into the cell.) Each day, your body produces millions of CD4+ T-cells to help maintain your immunity and fight off invading viruses and germs. Once HIV is in your body, the virus is able to copy itself over and over, increasing its ability to kill CD4+ T-cells. Soon, infected cells outnumber healthy T-cells.
The lower a person’s CD4+ T-cell count goes, the more susceptible the person is to viruses and infections that an otherwise healthy body could fight. In the initial stages of the infection, the decline in T-cell count is gradual. The first few months and years after a person is infected, T-cell counts may remain very near normal or only slightly decreased. It’s when T-cell numbers begin to dip dramatically that patients with HIV begin noticing additional, worsening symptoms of the infection.
The Four Stages of HIV
An HIV infection is typically divided into four stages: acute primary infection, clinical latent infection, symptomatic HIV infection, and progression from HIV to AIDS.
Acute Primary Infection
Within the first few weeks of contracting HIV, 70 percent of people will experience flu-like symptoms—fever, headache, upset stomach, and muscle soreness are among the most common initial signs of an HIV infection. A positive diagnosis is possible at this stage, but many will not associate their symptoms with an HIV infection, unaware they have contracted the virus.
During the acute primary infection, HIV-infected cells are circulating throughout the blood system. Your body responds by producing HIV antibodies and cytotoxic lymphocytes (killer T-cells that seek out and destroy invading viruses or bacteria). Two to four weeks after infection, the immune system mounts an attack against the HIV with these antibodies and killer T-cells. HIV levels in the blood will be greatly reduced, and CD4+ T-cell counts rebound slightly.
Clinical Latent Infection
The second stage of an HIV infection has an average duration of 10 years. During this phase, people infected with HIV live almost normal, asymptomatic lives because the infection has likely not caused any additional symptoms or complications. The circulating level of HIV in the blood will become very low and possibly almost undetectable. However, people with HIV remain infectious and can pass HIV to another individual during this phase.
Despite being present in very small amounts in your blood, HIV is very active in your body’s lymph system. Your doctor may suggest you start a drug treatment as soon as you are diagnosed. You may experience side effects as a result of this medication during this phase of your treatment. If you choose not to take medication, your doctor may want to monitor you regularly during the latency period to monitor the virus’s progress.
Symptomatic HIV Infection
Over time, HIV destroys your immune system. Once a person’s viral load (a measurement of how many cells in your blood are infected with HIV) begins dropping to lower and lower levels, this is an indication that the immune system is deteriorating; the disease is reaching a more advanced stage. If they are not already, many patients will begin treatment with antiretroviral medications at this point.
If the anti-HIV drug treatment does not work, or if a person chooses not to begin treatment, the immune system will begin to deteriorate more quickly. Initially, HIV-infected individuals will experience mild symptoms—fever, headache, and fatigue—but as the disease progresses, the immune system will weaken, and the symptoms will become worse. Symptoms of later-stage HIV infection include rapid weight loss, memory loss, recurring fever, and diarrhea that lasts more than a week. During this time, opportunistic infections become increasingly likely. These infections would not be a problem in a person with a normal immune system, but for people with a compromised immune system, they can become very troublesome. The infections are treated, but the progress of the disease cannot be stopped.
Progression from HIV to AIDS
In the final stage of HIV, the immune system is severely compromised. Infections become increasingly worse. CD4+ T-cell counts fall dramatically, and viral load increases significantly. When a person’s CD4+ T-cell count falls below 200 cells per cubic millimeter of blood and he or she is diagnosed with a stage-4 HIV-related condition (such as tuberculosis, cancer, and pneumonia), the HIV has progressed to Acquired Immunodeficiency Syndrome (AIDS). (The criterion for diagnosing AIDS differs from country to country. This is standard for the United States.) Once HIV progresses to AIDS, a person is more likely to die. Some patients will live only a few months after reaching the fourth stage of HIV; others will live many years. Thanks to new advances in medication, the life expectancy of people with AIDS is growing.