For instance, human immunodeficiency virus (HIV) infections, which lead to AIDS, affect the efficiency of the immune system. This means people with HIV and AIDS get more infectious diseases than a healthy person. A common infectious disease that occurs in HIV patients is tuberculosis. Tuberculosis is a bacterial infection, mainly affecting the lungs.
Viruses living in cells can be the trigger for cancers.
For instance, the majority of cases of cancer of the cervix are linked with a virus present in the female reproductive system called HPV.
The reaction of the immune system to pathogens and other foreign bodies can trigger allergic reactions that lead to skin rashes and asthma.
For instance, severe respiratory infections in babies can lead to asthma in later childhood.
Severe physical ill health can lead to depression and other types of mental illness.