Causative or Causal?

'Causal' means of or relating to cause or arising from a cause. 'Causative' means operating as a cause or expressing a cause. In describing an etiological agent, 'causative' is the accurate word. 'Causal' would be used to describe the relation between the agent and the infirmity.

I'd say that causative would mean that the agent is the direct cause of the disease, whereas if you use the word causal, I'd expect it to be perhaps one of several candidates, or perhaps one in a series of possible steps in causing the disease.