There is a version of Memory Loss in the Nipah Virus scenario which has a similar description to the Neurax Worm version. The only difference between the two is the ending sentence; "Very hard to cure" for the Neurax Worm and "Research doctors lose progress" in the Nipah Virus Scenario. It costs 13 DNA points. This symptom needs to be involved in order to unlock the Contagion Cancelled achievement.
Memory Loss is a symptom in the Frozen Virus Scenario, it causes recent memories to become vague historical recollections. It cannot be evolved without the DNA Repair 2 ability.