What to Know About HIV After Charlie Sheen's Announcement

— -- The announcement by actor Charlie Sheen that he is HIV positive is drawing attention to the virus that in recent years has become closer to a chronic disease than a death sentence.

During an appearance this morning on NBC’s “Today Show,” Sheen said he was diagnosed roughly four years ago after a series of debilitating headaches and excessive sweating episodes.

"I thought I had a brain tumor. I thought it was over," Sheen, 50, admitted. "It's a hard three letters to absorb. It's a turning point in one's life."

Dr. Larry Corey, a virologist and investigator at the nonprofit HIV Vaccine Trials Network (HVTN), said Sheen's experience of early HIV symptoms is common. After years in the body, the virus will start to have an effect on the immune system, which can lead to diagnosis.

“It’s fever, weight loss, headache, night sweats … or an infection like shingles” that leads to HIV diagnosis, Corey, also president emeritus of the Fred Hutchinson Cancer Research Center in Seattle, told ABC News. “A sense of loss of energy or fatigue or weight loss.”

Corey explained that despite medical advancements in treating the disease, HIV remains a huge problem in the United States. About 50,000 Americans are infected every year with the virus and up to 20 percent of those living with the disease aren’t aware they are infected.

There are an estimated 1.2 million Americans with the disease. Medications called anti-retrovirals were developed in the late 1990s and have since mostly prevented the disease from progressing to a fatal stage.

Corey said the medications have been so successful that the life span for a person with HIV is an estimated average of 40 years after diagnosis instead of an average of one year when the virus was first diagnosed in the early-1980s.

“It is suppressing it so that many, many, many complications are reversed,” Corey said. “We have good studies to show that the rate of transmission falls to very low levels.”

While the medications can drop viral levels until they are virtually undetectable, it is not a cure and someone who discontinues the medications can quickly develop the HIV virus again.

Corey said a key breakthrough would be the development of an HIV vaccine that would protect people from being exposed to the disease. A daily pill called a pre-exposure prophylaxis is now advised for people with behaviors that put them at risk for developing the disease.

When taken every day, the pill can significantly lower the chance of being infected with the virus.

Even with medications, however, HIV can lead to AIDS, which is deadly. About 13,000 Americans died of AIDS in 2013, according to the Centers for Disease Control.

Corey said having Sheen announce his status will, hopefully, make more people aware that the virus isn’t gone and additional work needs to be done to combat the disease.

“This epidemic has not gone away. It’s sort of the silent epidemic,” Corey said. “Worldwide, there are 2 million cases every year. Unfortunately, the disease is alive and well and thriving.”