Question

6) What are the "Components of the Chain of Infection"? 7) What is "incubation period" in a disease process?

Answer 1

6. The components if chain off infection are

Reservoir

Portal of exit

Mode of transmission

Portal of entry

Susceptible host.

The reservoir is the normal habitat in which the agent lives and multiplies. It is where the agent propagates itself in nature. The four types of reservoirs are:

• Symptomatic cases
• Carriers
  • Inapparent throughout history
  • Incubatory
  • Convalescent
• Animals
  • Direct zoonoses
  • Cyclozoonoses
  • Metazoonones
  • Saprozoonoses
• Inanimate objects
  • Water
  • Food
  • Soil
  • Air
  • Fomites

Portals of exit includes-

• Respiratory tract (upper and lower)
• Conjunctiva (lining of the eyes and eyelids)
• Urogenital tract
• Gastrointestinal tract (upper and lower)
• Placenta (mother to child transmission)
• Skin (broken and unbroken skin)

Modes of transmission include:

• Contact (requiring proximity to an infected host or discharge from an infected host)
• Vehicle (an inanimate intermediate carrier)
• Vector (an animate intermediate carrier, often an insect)
  • Mechanical
  • Developmental
  • Propagative
  • Cyclopropagative

Dynamics of Transmission

• Common vehicle
• Serial

Portal of entry

The portal of entry refers to the manner in which a pathogen enters a susceptible host. The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act. Often, infectious agents use the same portal to enter a new host that they used to exit the source host. For example, influenza virus exits the respiratory tract of the source host and enters the respiratory tract of the new host. In contrast, many pathogens that cause gastroenteritis follow a so-called “fecal-oral” route because they exit the source host in feces, are carried on inadequately washed hands to a vehicle such as food, water, or utensil, and enter a new host through the mouth. Other portals of entry include the skin (hookworm), mucous membranes (syphilis), and blood (hepatitis B, human immunodeficiency virus.

Susceptible host.

The final link in the chain of infection is a susceptible host. Susceptibility of a host depends on genetic or constitutional factors, specific immunity, and nonspecific factors that affect an individual's ability to resist infection or to limit pathogenicity. An individual's genetic makeup may either increase or decrease susceptibility.

7. Incubation period is the time from the moment of exposure to an infectious agent until signs and symptoms of the disease appear. For example, the incubation period of chickenpox is 14-16 days.

In biology, the incubation period is the time needed for any particular process of development to take place. For example, the length of time for turtle eggs to hatch is the incubation period.