Photo courtesy National Institute of Allergy and Infectious Diseases HIV, the virus that causes AIDS, is shown budding out of a human immune cell.

AIDS (Acquired Immuno Deficiency Syndrome) is one of the worst pandemics the world has ever known. HIV (Human Immunodeficiency Virus), the virus that causes AIDS, was first discovered in 1981 in a remote area of central Africa. It has since swept across the globe, infecting millions in a relatively short period of time. AIDS has killed more than 28 million people that we know of, with up to 3.6 million people dying in 2005 alone [Source: Avert]. While many cases go unreported, the prevalence of the disease is increasing. By comparison:

• The flu pandemic of 1918 killed approximately 20 million people worldwide.
• World War II killed approximately 40 million people.

Clearly the AIDS pandemic has had, and will continue to have, a significant and global impact.

In this article, we will show you how the HIV virus attacks the immune system and how it causes AIDS. We will also clear up some of the myths about AIDS and how HIV is transmitted.

The thought of contracting HIV is frightening. And there is good reason for that fear -- the disease is presently incurable, it has a high mortality rate, it spreads quickly and there is no vaccine to protect against it. In today's world, that combination is rare. For example, small pox is often fatal, but the disease has been completely contained through vaccinations. Tuberculosis is often fatal but can usually be cured with antibiotics if caught early.

AIDS has been able to infect and kill so many people because of its unique makeup. Let's look at some of the features that make this disease so unusual:

• HIV spreads by intimate contact with an infected person. Forms of intimate contact that can transmit AIDS include sexual activity and any sort of situation that allows blood from one person to enter another. Especially when you compare it with the many viruses that spread through the air, it would seem like the intimacy involved in the transmission of AIDS would be a limiting factor. However…

• A person can carry and transmit the HIV virus for many years before any symptoms show themselves. A person can be contagious for a decade or more before any visible signs of disease become apparent. In a decade, a promiscuous HIV carrier can potentially infect dozens of people, who each can infect dozens of people, and so on.

• HIV invades the cells of our immune system and reprograms the cells to become HIV-producing factories. Slowly, the number of immune cells in the body dwindles and AIDS develops. Once AIDS manifests, a person is susceptible to many different infections, because the immune system has been weakened so much by the HIV it can no longer fight back effectively. HIV has also shown the ability to mutate, which makes treating the virus nearly impossible.

The last feature in this list is the one that is truly unique. HIV invades and destroys the immune system -- the system that would normally protect the body from a virus. HIV corrupts and disables the system that should be guarding against HIV.

Next, we'll see how HIV can (and can't) be transmitted.