Final answer:
Certain factors must be present for a disease to occur, including the presence of a suspected pathogen, ability to isolate and grow the pathogen, and development of disease in healthy subjects. Pathogens must successfully achieve four stages of pathogenesis: exposure, adhesion, invasion, and infection. Environmental and social factors can also contribute to disease re-emergence.
Step-by-step explanation:
In order for a disease to occur, certain factors must be present. These include:
- The presence of a suspected pathogen: The pathogen must be found in every case of the disease and not be found in healthy individuals.
- Ability to isolate and grow the pathogen: The suspected pathogen can be isolated and grown in pure culture.
- Development of disease in healthy subjects: A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms as seen in diseased individuals.
Additionally, a pathogen must successfully achieve four stages of pathogenesis to cause disease: exposure, adhesion, invasion, and infection. The pathogen must be able to enter the host, establish an infection, evade the host's immune response, and cause damage to the host.
Environmental and social factors can also contribute to disease re-emergence, such as temperature, moisture, and sources of food or animal feed.