What it means to have HIV has changed dramatically

Actor Charlie Sheen appeared on the "Today" show Tuesday morning, November 17, to confirm that he is HIV positive.

Sheen is one of about 1.2 million people in the US and 35 million people around the world living with HIV, or human immunodeficiency virus. HIV can lead to acquired immunodeficiency syndrome, or AIDS. Unlike many other viruses, the body cannot get rid of HIV over time, so those that contract the virus have it for life.

Before the advent of effective treatments, AIDS was generally considered a death sentence. People whose HIV had progressed into AIDS lived an average of just ten years.

Today, however, there are a whole host of new treatments that reduce the amount of HIV in the blood (a measure called viral load) to levels where it is virtually undetectable. Thanks to these treatments, people around the world can expect to live on average about two decades longer than people diagnosed in 2001.

In wealthy countries especially, HIV has become more like a chronic illness than a death sentence. In the US and Canada, a 20-year-old diagnosed with HIV today is expected to live nearly as long as the average adult.

However, it's important to note that many treatments are still very expensive, and only available to those that can afford them. Less than half of people with AIDS are receiving treatment, according to The Economist. The majority of people with AIDS live in sub-Saharan Africa, and around the world, AIDS still kills more than a million people every year.

Still, in the US, most HIV patients are getting some form of antiretroviral therapy - a cocktail of pills designed to prevent the virus from making copies of itself. It reduces the viral load, suppresses symptoms, and makes it much harder for a patient to pass the virus to someone else. But it can be a challenge to get regular access to the pills, and the grueling treatment regimen also causes long-term liver damage in some patients.

There are some alternatives on the horizon. The FDA just approved a once daily pill called Genvoya that has better long-term safety than many other HIV drugs. And drug developers are working on an injection treatment that patients would only need every four or eight weeks. They would no longer have to remember to take a pill every day or pay for a lifetime supply.

Along with the rise of safe sex practices, there are also now pharmaceuticals that can prevent someone from getting the virus in the first place. When used correctly, a pill called Truvada can reduce the risk of HIV infection in people with a high risk of contracting it (those having unprotected sex with someone with HIV or taking intravenous drugs) by up to 92%. The problem is that it's only effective if you remember to take it every single day without fail.

Companies are also still trying to create an HIV vaccine that could eliminate the virus once and for all, though some medical professionals are skeptical that it can be done.

While the number of people with HIV is steadily declining, and the effectiveness of treatments is improving, AIDS remains a persistent global health crisis.

And a diagnosis can still come with a powerful stigma. Charlie Sheen said on the "Today" show that he paid people millions of dollars to keep his HIV-positive status a secret.

"I was more so afraid of the stigma attached to the disease than the actual disease," one patient diagnosed in 2007 told NPR.