Return of the Fourth Horseman: Emerging Infectious Diseases and
... disease spreads when a host organism transmits the agent to a
new organism. 21 Transmission can occur in many ways:
through air, water, direct contact with bodily fluids of a host
(e.g., urine, feces, saliva, and blood), sexual activity, and intermediary organisms or vectors (e.g., insects),2 Once a ...