I hope there's a cure for it

Large term cancer.

It's a very deadly disease for planets if you actually think about it in perspective, then they mutate and become airborne and very contagious, but some planets are more susceptible than others

Unfortunately, it's fatal with no known cure. Fortunately, the contagion is so aggressive, it may eradicate itself.

Ah, don't you worry, it's not gonna last for long time.