Based on the mode of transmission, diseases are classified as communicable or noncommunicable
diseases. Communicable diseases are transmitted from human to animal,
animal to animal, animal to human, and vice versa. The evolution of a
microorganism to the degree that it can survive in a different species or genetic environment
is a sign of an emergency. Pathogens can be directly transmitted through
inhalation or wounds and can be indirectly transmitted when a vector is involved in
the transmission process. Some pathogens produce free-living infective stages, and
when taken up by a susceptible host, they further grow using the host’s resources.
The results of studies involving the identification of mode of transmission of a disease
can significantly impact the action plan to contain the spread of disease. Such studies
not only predict the probable response of the disease to control efforts but can also
lead to further research on what happens when a pathogen is introduced in a system
in which it does not currently exist.