Regarding:
Giardiasis, shigellosis, amoebiasis & other infections of the intestinal tract.
Debateable:
Without treatment, all are fatal if they spread to the liver.
For some people:
Identifiable symptoms do not appear until the disease is well advanced.
Public Service Announcement:
You can catch a variety of jungle bugs, by drinking from a cup or glass at a restaurant - because the objects are not clean, because one or more handlers of the objects is/are not clean.
Careless personal hygiene.
FYI: HIV infection causes its infected to prematurely age 14 years. This info is hard to web search, which is why I tell you. If you want to learn more, check FR keywords HIVacceleratedAging and hivaging.