Is the max HP reduction from the Diseased Giant Rat permanent?

The variant Diseased Giant Rat (MM pg. 327) has a feature that when it hits with an attack and the target fails a saving throw, they contract a disease. The text says

Until the disease is cured the target can’t regain hit points except by magical means, and the target’s hit point maximum decreases by 3 (1d6) every 24 hours. […]

Is this reduction permanent or will the character regain their original maximum HP when cured of the disease?

My confusion stems from the fact that all information about the effect follows the "Until the disease is cured" statement, which could mean that the reduction only lasts until the target is cured. On the other hand one could argue that it is only further reductions that are mentioned and thus prevented by curing the target and the previous ones are separate effects that has already taken place.