Peptic ulcers are another well-known case, in which most (though not all) instances can be traced to a Helicobacter pylori infection. Other causal factors include NSAID usage, stress, and diet.

<https://en.wikipedia.org/wiki/Peptic_ulcer_disease>

<https://en.wikipedia.org/wiki/Timeline_of_peptic_ulcer_disea...>

One of the rare examples of a mental health condition being virtually completely eliminated is that of General paresis of the insane, a symptom of late-stage syphilis.

Successful treatment and elimination of syphilis in patients and populations through antibiotics. As one of the few cases of near-total elimination of a class of mental conditions, this a useful reminder to the psychiatric profession that not all mental conditions have causes limited to the brain and its function, whether through its biochemistry or neural/behavioural processes.

<https://en.wikipedia.org/wiki/General_paresis_of_the_insane>

> One of the rare examples of a mental health condition being virtually completely eliminated is that of General paresis of the insane, a symptom of late-stage syphilis.

I think a better example is the very recent (i.e., in the 2000s) discovery of anti-NMDAR encephalitis which can very closely resemble schizophrenia [1].

In syphilis, there were at least other manifestations of disease that can (and were) known, unlike this totally unappreciated mechanism (which better resembles Barry Marshall and H. pylori).

1. https://www.ncbi.nlm.nih.gov/books/NBK551672/