What disease disables the body's immune system untill it's no longer capable of fighting infection. what disease is being described

HIV or Human Immunodeficiency Virus is a viral infection, which directly attacks Leukocytes (white blood cells). Leukocytes are the cells responsible for fighting infections that break past the skin. If the infection is not controlled it can cause a range of disorder's which form a syndrome called AIDS or Acquired Immunodeficiency Disorder Syndrome. When this happen common infection for such thing as a common cold can turn lethal as the body is unable to fight pathogen's effectively. 

The answer is HIV, hope it helps