5. Definition
Factors
Infectious agent
An organism (virus, rickettsia, bacteria, fungus, protozoan,
helminth, or prion) capable of producing infection or infectious
disease
Properties of the agent: morphology, chemical composition,
growth requirements, and viability.
Interaction with the host: mode of action, infectivity,
pathogenicity, virulence, toxigenicity, antigenicity, and ability
to adapt to the host
Reservoirs
The environment in which a pathogen lives and multiplies
Humans, animals, arthropods, plants, soil, or any other organic
substance
Portal of exit
7. Direct: person to person
Indirect: implies a vehicle of transmission (biological or
mechanical vector, common vehicles or fomite)
Airborne droplets
Portal of entry
Means by which an infectious agent enters a new host
Respiratory passages, mucous membranes, skin, percutaneous
injection, ingestion, and through the placenta
Host susceptibility
The presence or lack of sufficient resistance to an infectious
agent to avoid or prevent contracting an infection or acquiring
an infectious disease
Biological and personal characteristics (e.g., gender, age,
genetics), general health status, personal behaviors, anatomical
and physiological lines of defense, immunity
Breaking the Chain of Transmission
Controlling the agent
Eradicating the nonhuman reservoir
9. an imprint of Elsevier Inc.
14
Table 25-2
Type
How Acquired
Length of Resistance
Natural
Active
Natural contact and infection with the antigen
May be temporary or permanent
Passive
Natural contact with antibody transplacentally or through
colostrum and breast milk
Temporary
Artificial