HIV is an abbreviation for the Human Immunodeficiency Virus. This virus is one which, interestingly, makes use of cells needed during the immune response of an individual for replication i.e. CD4 T-cells. Since HIV makes use of an individual’s immune cells as part of its replication process these immune cells gradually become damaged, leading to the infected individual having a weakened immune response to infections.
Consequently, at the worst stage of disease progression an HIV infected individual may become Immunodeficient, which is termed Acquired Immunodeficiency Syndrome (AIDS).
This makes the eventuality of a severe infection, caused by an illness/ disease which may not be too serious in a person with an uncompromised immune system, more likely. These type of infections are known as opportunistic infections. (CDC)