system
Given the following post, respond as if you're commenting on Reddit:
human
What does it mean to be immune to a disease, and how do "carriers" work?

From what I understand (I might even be completely wrong?) there is bound to be at least one person on this earth immune to disease X, they could carry it and spread it - but not be affected and killed by it. How does this work? Does their immune system not care about the disease or just isolate it in the body? What happens?
gpt
There are different kinds of immunity.  If the infectious disease cannot grow in the host or has been completely wiped out, then they can't be a carrier.  This can happen several ways, for example:

1.  The disease has been completely obliterated by the concerted effort of your immune system or through drugs.  For example, if you clear a yeast infection completely, you can't give it to someone else afterwards because there's simply no yeast left.

2.  Certain people are naturally immune to certain types of disease because of there genetics.  For example, some people are immune to HIV because they don't have a receptor that HIV attaches to.  If the virus can't enter the cells, it can't infect and be passed on.

However, there are other disease that the host can contain (maybe for a little while anyway) and render asymptomatic but cannot completely clear, even with the help of drugs.  These include herpes, HIV.  The disease has mechanisms to avoid or suppress the immune system enough that there aren't any symptoms, but the disease can still be transmitted.  Every disease has it's own way of doing though.  Typhoid fever, for example, can be asymptomatic in a host, but still be tranmissible because in certain people the bacteria can "hide" from the host immune defense.