Sure looks like chalkbrood to me.
There is no treatment for chalkbrood. Usually I just try and improve ventilation, give the hive a boost and when all else fails (only happened once) I've requeened. It is a spring time phenoma, phenome, phenomi.............................phenomenon, and almost always clears up as the colony gets stronger.
If there are only a few cells I wouldn't worry too much. I've taken frames from hives that had it, popped them into a strong hive and the next day the strong hive has cleaned out all the mummies and things are good.