Chapter 1: Establishment of Infectious Diseases

What are the domains of the tree of life?

Bacteria, Archaea, and Eukarya

Prokaryotes

A single-celled organism that lacks a distinct, membrane-bound nucleus and other internal cell parts called organelles.

ex: Bacillus Megaterium; Escherichia coli

Eukaryotes

An organism whose cells contain a distinct, membrane-bound nucleus and other specialized, membrane-bound structures called organelles

e.g., Amoeba, Saccharomyces cerevisiae, and Chlamydomonas nivalis

Who is the father of microbiology

Louis Pasteur

Who is the father of medical microbiology

Robert Koch

Koch’s postulates

Present in all cases of the disease.

Isolate the microorganism from the diseased host and grow it in pure culture.

Inoculate a healthy host → it develops the same disease.

Re-isolate the same microorganism from the newly infected host.

Memory trick: P → I → I → R

Present → Isolate → Inoculate → Re-isolate

To develop a conceptual framework based on two generalizations

(i) in all IDs, the following events take place: encounter, entry, spread, multiplication, damage, outcome

(ii) each of these events requires the breach of host defenses; the manner distinguishes one parasite from another

Encounter

• We first encounter microbes at birth

• Fetus lives in a sterile environment

• “Congenital infections” (e.g., syphilis, AIDS)

Types of encounter:

(i) exogenous (agent in the environment)

(ii) endogenous (agent present in or on the human body, e.g. the normal flora)

Encounter does not always lead to a disease (# of microbes, age, nutritional state, …)

Entry

• Ingress: entry without crossing epithelial barriers (e.g., via toxins)

• Penetration: entry into tissue after crossing epithelial barrier

via receptors

insect bites

cuts & wounds

organ transplants & blood transfusions

Inoculum size in infection

Regions of the body in direct contact with the exterior

Spread

• Anatomical factors

• Active participation by microbes

Multiplication

• Environmental factors

• Subversion of host defenses

Microbial Multiplication and Clinical Manifestations of Disease

Damage & Outcome

• Cell death

• Tissue, organ damage

What diseases are spread by inhalation, and what causes them?

• Common cold → Virus → Aerosols from infected people

• Coccidioidomycosis → Fungus → Soil

What are the key facts about typhoid fever?

ingestion → Bacterium → Water/food → Sanitation → Lower infecting dose

What are the key facts about gonorrhea?

Sexual contact → Bacterium → Person → Social behavior → Avoid contact

What are the key facts about surgical infections?

Wound → Bacteria → Normal surrounding flora → Aseptic techniques → Avoid contact

What are the key facts about malaria?

Insect bite → Protozoan → Mosquito → Insect control → Eliminate vector

What are the main prevention strategies in the table?

• Typhoid → Sanitation

• Gonorrhea → Social behavior

• Surgical infections → Aseptic techniques

• Malaria → Insect control

• Inhalation diseases → None