What are infectious diseases?
Infectious diseases are caused by
pathogenic microorganisms, such as bacteria, viruses, parasites or fungi. These
can be spread directly or indirectly from one person to another or else from
animals, latter known as zoonotic diseases.
For an organism to cause
infection, it needs to follow a chain of infection. An infectious disease
result from the interaction of an agent (organism), host (reservoir) and the
environment. Transmission of infection occurs when the agent leaves the
reservoir through a portal of exit and enters through an appropriate portal of
entry to infect a susceptible host (as seen below).
Transmission can be by direct
contact e.g. droplet spread or else indirect contact such as airborne
transmission, vehicle-borne or vector borne transmission.
