One disease can make another more likely. HIV is a virus that infects and damages white blood cells, so it weakens the immune system. If HIV is not controlled, it can lead to AIDS, when the immune system is so damaged that it can no longer fight off many other infections.
Tuberculosis (TB) is a bacterial disease that mainly affects the lungs. Many healthy people carry the bacteria without becoming ill because their immune system keeps them under control. In a person with HIV the weakened immune system cannot do this, so active tuberculosis is much more likely.
A communicable disease can also lead to a non-communicable one. The human papilloma virus (HPV) infects cells of the cervix. In some women this infection makes the cells divide in an uncontrolled way and can lead to cervical cancer. A vaccine against HPV is offered to teenagers to reduce the risk.