Which Biological Safety Level is reserved for biological agents that can cause potentially severe or fatal disease in humans, but for which effective treatments (for example, antibiotics or vaccines) exist?

Biological safety level 3

Explanation:

BSL are ranked from one to four depending on the agent or the organism that is being researched on.

BSL1 is the lowest lab level and it deals with organisms that are non lethal.

BSL2 work with agents that cause moderate health hazard.

BSL3 is the one reserved for research with biological agents that can potentially cause severe/fatal disease to humans however there is a treament or vaccine to the disease

BSL4 are rare. They handle highly dangerous microorganisms that do not have treatment or vaccine.