Honeybees are incredible (well we think so anyway).
You may know that they keep intruders out of their hives by stinging or balling them. If stinging the invader does not work, they will ball the invader, heating them up to the point where they cook them. Both Asian and European honeybees do this.
It's fascinating how they keep intruders out, but what about diseases and viruses? Bees groom themselves, often before entering the colony, similar to how humans shower. Consider for a moment how quickly illness spreads in a school setting. It can spread just as quickly within a honeybee colony. This is why it is so important for the colony to have a structure in place to deal with it.
Undertaker bees: These middle-aged bees have the job of taking the dead bees out of the hive. This limits exposure to the colony if they died from a virus or illness of some sort.
Propolis: Bees use propolis (bee glue) to close gaps, holes and drafts in their hive. In doing so, they block the entrance to viruses, pests, bacteria, fungus and disease. Propolis is made of a mixture of plant resin and wax.
Most hive bodies are sold with smooth sides. The best hive bodies are rough on the inside. These hives mimic the inside of a tree cavity, allowing the colony to place propolis along the entire hive body, keeping the colony healthy.
(Information from Master Beekeeping program at Cornell)