With the disease resisting, Thaum channels mana to remove any curse there may be, then attempting to remove the disease again.

Spoiler: Actions
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Casting remove curse until he succeeds the CL check. If the disease persists after a success, he tries to heal the disease again.
Caster level checks
(1d20+9)[25]
(1d20+9)[28]
(1d20+9)[21]
(1d20+9)[15]
(1d20+9)[19]