Intro to Infectious Disease

Question 1

What is a pathogen, and what is the difference between primary and opportunistic?

Answer 1

Any disease-causing microorganism

Primary - Cause disease in any host

Opportunistic - only cause disease in hosts with impaired or damaged defense mechanisms

Question 2

What is virulence?

Answer 2

The ability of an organism to cause disease

avirulent organisms can not or ordinarily do not cause disease

Question 3

What are three general routes of transmission for disease-causing agents?

Answer 3

Exogenous human to human

Exogenous animals to human (zoonotic infections)

Endogenous agents part of normal flora

Question 4

What are three methods of human-human transmission?

Answer 4

Respiratory or salivary spread (sneezing)

Fecal-Oral

Venereal

Question 5

What are three methods of arthropod-borne and zoonotic infections?

Answer 5

Vector (biting arthropod)

Vertebrate reservoir

Vector-vertebrate reservoir

Question 6

What are fomites?

Answer 6

Inanimate objects which can harbor microorganisms

E.g. infant toys, toothbrushes

Question 7

What is the most common source of human infections?

Answer 7

Normal flora

They are moved from their normal habitat and invade areas which are normally sterile (blood, muscle, alveoli)

Question 8

What is the most complex source of microorganisms in the body?

Answer 8

Large Intestine

Question 9

What are the beneficial effects of normal flora?

Answer 9

Production of nutrients (e.g. Vit K)

Occupation of habitat (prevents occupation by pathogens)

Elaboration of bacterial toxins

Stimulation of immune response

Question 10

What are Bacteriocins?

Answer 10

High pH, toxic bacterial proteins that kill other bacteria

Question 11

What are general mechanisms underlying opportunistic infection?

Answer 11

Comprised Host

Breach of host surfaces

Use of antibiotics - wipe out intestinal flora

Question 12

What are Koch’s Postulates?

Answer 12

Bacterium found in all diseased people, in affected body parts

Bacterium isolated from the lesions of an affected persons and maintained in pure culture

Pure culture, inoculated into human or animal, should reproduce the disease symptoms

Same bacterium should be reisolated from the infected animal or human

Question 13

What are limitations to Koch’s Postulates?

Answer 13

Ignores host susceptibility and resistance

Importance of being able to culture bacterium, many can’t be cultured

Variability in virulence of single bacterial species

Ethics of inoculating humans with pathogens

Polymicrobial infections

Question 14

What are bacteria?

Answer 14

Unicellular prokaryotic organisms

Most have cell walls

Question 15

What are Fungi?

Answer 15

Eukaryotes with a nucleus, organelles, and a cell wall

Include yeasts, molds, and dimorphic fungi

Question 16

What is the difference between yeasts and molds?

Answer 16

Yeasts are unicellular

Molds are multicellular or filamentous

Question 17

What is the microbial definition of parasites?

Answer 17

Unicellular or Multicellular eukaryotic organisms that require a living host for at least part of their life cycle and cause disease in the host

This definition excludes bacteria and viruses

Question 18

What are viruses?

Answer 18

Intracellular parasites that lack cell structure

Generally consist of nucleic acid genome surrounded by a protein coat (capsid)

Question 19

What are the two types of viral infection?

Answer 19

Lytic cycle - one or a few viruses infect a cell, replicate within and produce 1000s viruses that are released by lysis of the host cell

Persistent or Latent infections - animal cells are not lysed by rather harbor the viral genome or allow the replication of low number of viruses

Question 20

What are prions?

Answer 20

Infectious agents consisting only of protein

E.g. Bovine Spongiform Encephalopathy (Mad Cow), Scrapie, Creutzfeldt-Jakob

Question 21

What are viroids?

Answer 21

Consist of RNA genome without any protein components (Hep Delta)