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USW1_PUBH_3100_W3SlidesInfectiousDisease.pptInfectious Disease Process
Infectious Disease Process
and
Chain of Infection
Dr. John Kowalczyk
Walden University
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
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Infectious Disease Process
- Results from the interactions of the three components of the epidemiologic triangle:
Agent
Host
Environment
- Chain of infection includes six chain links that all must happen in succession—break any link in the chain, the disease spread will cease.
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection
Host
Susceptibility
Means of Entry
Mode of
Transmission
Means of
Escape
Reservoir
Pathogenic
Microorganism
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #1: Pathogenic Microorganism
Causative Agent
- The entity capable of causing disease
- Agents are one of three types:
Biological: protozoa, metazoa, bacteria, viruses, fungi, rickettsia
Chemical: pesticides, additives, industrial chemicals
Physical: heat, light, ionizing radiation, noise, vibrations
*Note: Most diseases are caused by biological agents; chemical and physical agents cause chronic long-term illnesses.
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #2: Reservoir
Reservoir of Agent
- The normal habitat in which an infectious agent lives, multiplies, and grows
- These habitats include humans, animals, and environment
- Two major categories of human sources of infection:
- Acute clinical cases
Less likely to cause transmission due to early diagnosis and treatment (e.g., going to a doctor)
- Carriers: People who harbor infection but have no overt signs or symptoms.
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #3: Means of Escape
Portal of Exit of Agent from Host
There are five means of exit from the human body:
Respiratory tract: very common but difficult to control
Common cold
Influenza
Tuberculosis
Airborne droplets
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Portal of Exit of Agent from Host
Genitourinary tract: urine, semen
Syphilis
Gonorrhea
Schistosomiasis (blood flukeworm inside body, eggs leave through urine—e.g., urinate in the lake; eggs enter skin while wading in water and then enter bloodstream)
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Portal of Exit of Agent From Host
Alimentary tract: mostly related to food; by mouth; also vomitus, feces, saliva
Rabies—dog bite
Cholera—intestinal tract
Skin
Superficial wounds—cuts, gashes, burns, puncture wound
Smallpox
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Portal of Exit of Agent From Host
Transplacental mode (mother to fetus): pregnant woman passes disease thru placenta/umbilical cord to baby
Rubella
Syphilis
Hepatitis B
HIV+
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #4: Mode of Transmission
Mode of Transmission of Agent to New host
- Direct transmission (person to person): touching, biting, kissing, sexual intercourse
- Indirect transmission:
- Vehicle borne (inanimate): blood, water, food, surgical equipment, eating utensils, clothing
- Vector borne: feces, eggs, biting (saliva)
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #5: Means of Entry
Portal of Entry Into New Host
- Basically the same as link #3: Means of Escape
- Mouth, nose
- Skin
- Genital/anal
- Transplacental (mother to child)
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
Chain of Infection #6: Host Susceptibility
Host susceptibility
Depends upon:
- Genetic factors
- General resistance
- Specific acquired immunity (natural or thru vaccinations)
+skin toughness -malnutrition
+gastric acidity -poor health
+cough reflex -repressed immune system
© 2011 Laureate Education, Inc.
© 2011 Laureate Education, Inc.
*
