HIV/AIDS: From Epidemic to Pandemic

From Epidemic to Pandemic

As the AIDS epidemic grew unabated in the United States, numerous cases appeared in Europe, South America, and Africa. While disease transmission was generally associated with gay men in the United States, disease transmission in other parts of the world was linked to heterosexual contact. In 1990, the World Health Organization (WHO) estimated that about one million people were living with AIDS. In less than 10 years, HIV had exploded worldwide.

In the early and mid-1990s, extensive education programs in North America and Europe, stressing the need for protection from bodily fluid transfer, helped to slow the spread of AIDS. Yet, around the world, the number of AIDS cases continued to rise. According to WHO, in 2001 an estimated 40 million people, 37.2 million adults and 2.7 million children, were living with HIV. Twenty years after the first cases were reported, a modern pandemic is ravaging the world's poor.

Most striking are the 28.1 million AIDS cases in Africa, with most in sub-Saharan Africa. Nearly 2.3 million Africans died from AIDS in 2001, and without adequate treatment and care, many more will die. Other countries, like India, are experiencing meteoric rises in AIDS cases. Some countries with little history of AIDS, like China and Russia, are poised for a major epidemic as well.

Clinical Definition of AIDS

The, CDC defines AIDS in an adult or adolescent aged 13 years or older as the presence of one of 25 conditions that indicate that the immune system is severely compromised because of HIV infection. People with HIV are also defined as having AIDS once their CD4 + T cell count goes below 200 cells per cubic milliliter of blood (normal CD4 counts are between 500 and 1600 per cubic milliliter).

AIDS refers only to the end stage of a progressive disease that starts with HIV infection and leads to severe impairment of the immune system. Once the immune system is weakened, AIDS patients are susceptible to other infections and cancers. These infections are called opportunistic because the organisms that cause them take advantage of the person's weakened immune system and cause disease.

HIV, the Cause of AIDS

In 1983, Dr. Luc Montagne and colleagues at the Institute Pasteur in France reported that they had isolated a new virus called lymphadenopathy-associated virus, or LAV, which was the cause of AIDS. A short time later, in 1984, Dr. Robert Gallo and colleagues at the National Cancer Institute (NCI) reported that they had isolated a virus called HTLV-III, which was believed to cause AIDS. Both were right, as the virus from French and American groups were nearly identical. Sometime later the virus was renamed human immunodeficiency virus, or HIV. It belongs to the family, or group, of retroviruses called lentiviruses, which are found in a wide range of nonhuman primates.

A retrovirus's genes are made up of RNA, and so they need to live in a host and “borrow” the host's DNA in order to multiply.

The Koch Test

Nearly all scientists recognize that HIV is the cause of AIDS. However, a small and vocal minority of researchers have argued that AIDS is not consistent with a single disease caused by a single infectious agent.

German bacteriologist Robert Koch (1843-1910) developed a series of rules, or postulates, for deciding whether a microbe is responsible for a specific disease. These four postulates stipulate that an infectious agent must be found in all cases of the disease; the agent must be isolated from the host's body; the agent must cause disease when reintroduced into a healthy host; and the same agent must once again be isolated from the newly diseased host. As you'll see in the following examples, all four postulates have been fulfilled for HIV, convincingly identifying HIV as the cause of AIDS.

The mature HIV is roughly spherical. The outer envelope is studded with two major proteins (gp120 and gp41). The central core contains viral proteins (p24 and p17), two copies of the HIV RNA genome, and three viral enzymes essential for viral replication.

• In the mid-1980s, laboratory workers studying HIV in isolation were accidentally exposed to high concentrations of the virus and later developed weakened immune systems and opportunistic infections characteristic of AIDS. HIV was isolated from the lab workers' blood, and it was shown to be the same infecting strain. The same observations have been made for health-care workers accidentally infected by puncture wounds from HIV-contaminated needles.
• The development of AIDS following known HIV exposure has been routinely observed in blood transfusion cases, mother-to-child transmission, injection-drug use, and sexual transmission. In these cases, the identification of HIV in the blood has been documented using blood samples taken before and after infection.
• HIV-infected mothers have been known to give birth to twins where one twin is HIV-positive and develops AIDS, while the other child shows no sign of HIV and remains clinically and immunologically normal.
• Numerous studies of HIV-infected people show that the amount of HIV in the body correlates with the progression of the clinical symptoms of AIDS.
• Nearly everyone with AIDS has antibodies to HIV.
• Before the appearance of HIV, AIDS-related conditions such as Pneumocystis carinii pneumonia (PCP), Kaposi's sarcoma (KS) and infection with Mycobacterium avium complex (MAC) were extraordinarily rare in the United States.
• HIV has been repeatedly isolated from the blood, semen, and vaginal secretions of patients with AIDS, which is consistent with findings linking AIDS transmission via sexual activity and contact with infected blood.

Infection and Disease

Infection begins when an HIV particle encounters a specialized immune cell, a T cell. The virus particle attaches itself to the cell's outer surface membrane and enters the cell. Once in the cell, the virus releases its RNA, and a chemical converts it into HIV DNA. The new HIV DNA moves into the cell's nucleus and strong-arms the host cell to help make copies of the virus, releasing new infectious virus particles.

The rate of disease progression depends on several variables, including the health of the host and the particular strain of the virus. However, the median time from initial infection to the development of AIDS among untreated patients is typically 8 to 10 years.

HIV damages the body's sources of T cells and centers of immune activity, killing cells in the bone marrow and thymus that are needed for the development of mature immune cells. The virus also progressively destroys the lymph nodes, the centers of immune activity in the body. The viral load, or amount of virus in circulation, is a barometer of disease progression.

Opportunistic Infections

The relative risk of developing opportunistic infections is closely tied to T cell counts. As T cell counts go down, many different organisms can cause infections. Common AIDS-related opportunistic infections are caused by fungi like Candida (topical and systemic yeast infections), bacteria like tuberculosis, and viruses like hepatitis and herpes.

HIV Symptoms

Early symptoms of HIV infection include …

• Swollen glands
• Night sweats or continuous fever
• Unexplained weight loss exceeding 10 pounds
• Heavy, continual dry cough
• Shortness of breath
• Oral thrush
• Recurrent vaginal yeast infections
• Unexplained skin rashes
• Herpes infections that require a long time to heal

A common physical manifestation of late-stage AIDS is the “Wasting Syndrome,” when body fat and body mass are significantly decreased, making a person look like they are suffering from severe malnutrition.

Excerpted from The Complete Idiot's Guide to Dangerous Diseases and Epidemics © 2002 by David Perlin, Ph.D., and Ann Cohen. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.