What disease begins with a flu-like illness and progresses to attack the immune cells if it isn't successfully controlled?

The disease that begins with a flu-like illness and progresses to attack the immune cells if it isn't successfully controlled is HIV/AIDS. Here are the steps of how it progresses:

1. Initial Infection: The person may experience a flu-like illness within 2-4 weeks after the HIV virus enters the body. This is known as primary or acute HIV infection.

2. Asymptomatic Stage: After the initial symptoms disappear, HIV may not cause any further symptoms for many years. During this time, the virus continues to be active and causes progressive damage to your immune system.

3. Advanced Infection: If left untreated, the immune system weakens, leading to "Acquired Immunodeficiency Syndrome" (AIDS). At this stage, the person is more susceptible to infections and diseases that the body would normally resist.

4. Opportunistic Infections: These are infections that occur more frequently and are more severe in individuals with weakened immune systems, including people with HIV.

5. Progression to AIDS: If not treated, HIV can lead to AIDS, the final stage of infection. People with AIDS have such badly damaged immune systems that they get a number of severe illnesses.

It's important to note that with early diagnosis and effective antiretroviral treatment, people with HIV can live a normal, healthy life.