HIV biology and challenges in fighting the virus
Visit "Life Cycle of HIV Infection & Sites of Current Drug Action" (prepared by JHU AIDS Service)33 to view the "HIV Life Cycle" in Flash animation. Read AIDS Basics for a beginner's guide to HIV and AIDS.
HIV Biology and Epidemiology. Infection with the "human immunodeficiency virus (HIV)" occurs through exchange of bodily fluids with a partner or source already infected with the "HIV". This exchange of bodily fluids could be through sexual contact (semen, vaginal secretions), blood transfusion (e.g., blood), injection (e.g., accidental needle prick, injection drug use). [Visit Transmission of HIV for more detailed links to the modes of transmission of the virus.]
HIV targets the immune system and other parts of the body. In more advanced stages, the immune system is so compromised impairing the ability of the body to fight infections; thus, the term "acquired immunodeficiency syndrome (AIDS)". As a result, those at advanced stages of HIV infection become vulnerable to a range of AIDS-related illnesses and other opportunistic infections, e.g., Pneumocystis pneumonia, Kaposi's sarcoma, tuberculosis (TB), cryptococcal meningitis, etc. The more common opportunistic infections vary from one region to another. Pneumocystis pneumonia and Kaposi's sarcoma are more common in the United States, while tuberculosis (TB) is more common in Africa.
While AIDS first ravaged gay men in the United States and other Western countries, it became apparent from its mode of transmission that HIV can target any group. In fact, heterosexual transmission is a major mode of HIV infection in other parts of the world. Even in Western countries, including the United States, Canada, United Kingdom, recent evidence indicated an increased rate of HIV infection through heterosexual transmission, especially among women.
Medical breakthroughs. The discovery of the virus by Luc Montagnier in France and further characterization of the HIV by the group of Robert Gallo in the United States in the 1980's led to a worldwide frenzy in the study of the biology of the virus.
These and subsequent discoveries led eventually to better and rapid HIV screening procedures based on the antibodies produced by the body to fight HIV infection. Advances in other areas of basic biology, e.g., PCR technology, eventually led to even more sensitive, faster and automated screening of the virus based on the DNA structure. The very sensitive PCR-based screening also allowed "more immediate detection" from the onset of infection . The latter technology was very critical in further elucidation of how the virus attacks various parts of the body and how it integrates itself to various host cells upon infection.
Understanding of the biology of HIV and progression of the disease also led to improved medical care in controlling the progression from HIV infection to AIDS status. These led also to important discoveries in antiretroviral and combination drug therapies that have allowed people living with HIV or AIDS to live longer with a "manageable disease".
With all these breakthroughs, Western countries made headway in the fight against AIDS. In the United States, new cases of peaked in 1993 and AIDS deaths peaked by the mid 1995 and started significant declines thereafter (see figure below).
The recent dramatic drop in fatalities, among those with AIDS in Western countries, arose from significant progress in drug development to avert the progression of the disease and controlling other AIDS-related diseases and opportunistic infections. However, these drugs are prohibitively costly so that they are essentially out of reach to people living with HIV/AIDS in many of the less developed countries. Moreover, the HIV strains prevalent in Western countries -- where most of the antiviral drugs were developed -- are quite different from the HIV strains found in other parts of the world. It is possible that this HIV strain variation may reduce the efficacy of the drugs when used against the HIV strains that are more prevalent in other countries.
Aside from the variety of HIV strains found in different parts of the world, a more serious concern is the ability of the different viruses to mutate quite rapidly. This results in rapid development of viral resistance to current drugs against AIDS. As a result, while there has been dramatic decrease in death from AIDS-related illnesses and opportunistic infections during the latter part of the 1990's, the decline has started to level off.
A more worrisome consequence of the recent success with antiretroviral and combination therapies is a misplaced notion that the AIDS epidemic has been vanquished, at least in the United States and other Western countries. This false sense of security may be contribute to the resurgence of new cases of HIV infection, especially among young people.
Moreover, new cases of HIV infection and AIDS in the United States (US) disproportionately affect the poor and certain minority populations, especially African-Americans and Hispanics. Thus, while AIDS is no longer among the top 15 major causes of death in the US, it has become one of the major leading causes of death among African-Americans aged 25-45. The impact of the disease among these minority populations reflect a pattern more common in less developed countries.
The development of vaccines against HIV would be a more economically feasible strategy of combating the disease, especially in less developed countries. So far, the development of such an "AIDS vaccine" has eluded the scientific community. Moreover, even with successful development of AIDS vaccines, the efficacy of these vaccines against HIV can be thwarted by the rapid mutation of the various HIV strains.
With increasing globalization, other HIV strains may find their way to other parts of the world via defined modes of transmission. The different HIV strains have cell targets that may be have a bearing on their modes of transmission. If the latter hypothesis is correct, specific modes of transmission of HIV may reach a critical level also in Western countries, if certain HIV strains become more globally ubiquitous.