The agent by which an infection is capable of being transmitted by direct or intimate contact (e.g., sex). These agents include viable microorganisms including bacterium, virus, rickettsia, parasite, fungus, or recombinant, hybrid or mutant that is known or reasonably believed to cause disease in humans or animals.
The chemical organism that causes a particular disorder. Scientific opinion is divided about the biological nature of the agent that causes SEs. The two main theories are the Prion hypothesis and the Virus theory.