The disease described as beginning with a flu-like illness and progressing to attack immune cells if not successfully controlled is Human Immunodeficiency Virus (HIV) infection. HIV initially causes symptoms similar to the flu during the acute phase, often with a high level of virus detectable in the blood. The virus specifically attacks CD4+ T cells, which are crucial for coordinating the immune response. Over time, as HIV depletes these immune cells, the immune system becomes severely compromised, leading to the condition known as acquired immune deficiency syndrome (AIDS), where opportunistic infections and diseases occur due to the weakened immune defenses.
Other diseases involving flu-like onset and immune system involvement, like severe influenza or viral infections with cytokine storms, involve immune reactions but do not primarily attack immune cells in the progressive manner seen in HIV.
Thus, the best fit for the described disease is HIV infection.
