The paper says that 100% of the control group died. (This is a mouse model and a virus specifically selected to be deadly.) So, not "toxic", and not the usual

The paper says that 100% of the control group died. (This is a mouse model and a virus specifically selected to be deadly.) So, not "toxic", and not the usual LD50 that's often misreported as "lethal". But still, the language seems appropriate.