grammaticality - Inversion in "Only when the virus introduces its nucleic acid into a cell does disease occur"

Given this sentence,

Disease occurs only when the virus introduces its nucleic acid into a cell.

Is the following inversion grammatical?

→ Only when the virus introduces its nucleic acid into a cell does disease occur.

Especially the "does disease occur" part.

I think that "occurs disease " is right. Can you explain a rule about this kind of sentence?