Overview
HIV produces an average of about 10 billion new viruses daily. These new viruses attack and kill CD4 cells, destroying 10 billion CD4 cells each day. The immune system retaliates by replacing the lost CD4 cells.
In the long run, however, the virus reproduces more effectively than the immune system retaliates, and over a period of years, the number of CD4 cells gradually declines.From the point of view of the person with HIV infection, the battle within—the fight between HIV and the CD4 cells—is silent. The person remains asymptomatic until the immune system begins losing the battle. The average person has 1,000 CD4 cells per milliliter of blood—a total of about 100 billion CD4 cells in the body—and does not become vulnerable to complications until the CD4 count falls to 200 cells per milliliter or less. HIV-infected people with CD4 counts above 200 usually deal with the microbial world with aplomb. There are a few exceptions, but not many. Most people actually do well until the CD4 count is substantially lower than 200. The average CD4 count with the first major complication is about 50.
For about 50 percent of people with untreated HIV infection, this first complication occurs within ten years of being infected; this is only an average. A very few people, less than 1 percent, progress rapidly from infection to an AIDS-defining diagnosis within one year. At the other extreme are the people who go for years without any apparent consequences of HIV infection: they have no symptoms, and the number of their CD4 cells is normal. Some of these people go without consequences long enough that they are called “chronic non-progressors.” To be chronic non-progressors, people must meet three criteria: they must have had HIV infection for at least eight years; have a normal CD4 cell count (see below); and have received no treatment against HIV.
Apparently 2 to 3 percent of people with HIV infection are chronic non- progressors. The reason for non-progression may be that these people have been infected with an especially hapless virus. The reason may also be that many of these people have a robust immune response—a highly effective CD4 response that’s specific to HIV. This latter reason is more common.The reasons that people progress to the first complication vary. Many people never knew they were infected until this first complication prompted them to get their first HIV tests. Other people failed therapy. Some refused therapy. Many were depressed or substance abusers. For those who are newly diagnosed and whose first complication has not left permanent damage, the prognosis is excellent.
The stage at which the first symptoms or conditions of a weakened immune system occur usually happens five to eight years after infection. This stage may or may not mean that the immune system is weakening. The most common early conditions are thrush, oral hairy leukoplakia, shingles, and idiopathic thrombocytopenic purpura. Some of these complaints are experienced by people who do not have HIV; the biggest difference is that in someone with HIV infection, the symptoms tend to be chronic, that is, they persist for several weeks or months. Most people with these early symptoms have a relatively low CD4 cell count, usually less than 300; most people have no symptoms until the CD4 cell count is less than 50.
The late stage of HIV infection, usually eight to ten years after infection, entails severe immunosuppression, that is, severe weakening of the immune defenses of the body. The exact definition of AIDS has historically been a moving target, but in 1993 the definition was set to include anyone with HIV infection and a CD4 count below 200. People with AIDS are susceptible to opportunistic complications caused by microbes to which everyone is exposed on a regular basis but which are usually defeated by a modest effort of the immune system.
The most common and important complications are described below. Pneumocystis jiroveci pneumonia and Kaposi’s sarcoma are the most common of the complications; the others occur less frequently.This whole process is highly variable. Based on four different studies (done before any effective treatment was available), the time lapse between transmission of HIV and AIDS is as follows: after 1 year, 0 percent of the people with HIV infection were diagnosed with AIDS; after 2 years, 0 percent; after 3 years, 3 percent; after 4 years, 6 percent; after 5 years, 12 percent; after 6 years, 20 percent; after 7 years, 27 percent; after 8 years, 36 percent; after 9 years, 45 percent; after 10 years, 53 percent. Some people with AIDS lived five years or more after their first major complication, without therapy, but they were unusual.
HIV infection, untreated, affects virtually every part of the body. The virus’s effect is either indirect—through medical complications—or direct. Moreover, its effects, both direct and indirect, resemble symptoms of other diseases. As a result, people easily become confused and worried: Which symptoms should I see the doctor about? Which should I ignore? Which result from HIV infection and which are the normal flus and headaches everyone has? How are the complications diagnosed? What are the usual treatments? What are the side effects of the treatments?