Chapter 1: Pathogens as parasites

Question 1

List four reasons for resurgence of infectious disease.

Answer 1

1. New patterns of travel and trade, altered sexual behavior, overuse of antibiotics.
2. Movement of multi-drug resistant bacteria from healthcare settings to community.
3. Breakdown of economic, social, and political systems (weakened medical services and increased poverty)
4. Increase in air travel

Question 2

What are some key differences between prokaryotes and eukaryotes?

Answer 2

Prokaryotes: no nucleus; no membrane-bound organelles; DNA is a single, circular chromosome; extracellular DNA is carried as plasmids; transcription and translation can be carried out simultaneously
Eukaryotes: membrane-bound nucleus and organelles; DNA is composed of several linear chromosomes; transcription and translation are carried out separately (transcription in nucleus and translation in cytoplasm)

Question 3

List the microparasites and their site of replication. Are they intra- or extracellular?

Answer 3

viruses, bacteria, protozoa, fungi
They replicate within the host and produce large numbers of progeny
They are intracellular

Question 4

List the macroparasites and their site of replication. Are they intra- or extracellular?

Answer 4

worms, arthropods
The infectious stage matures to reproducing stage, may leave host to continue cycle
They are extracellular

Question 5

What advantages does intracellular life have for pathogens?

Answer 5

provides access to the host’s nutrient supply and its genetic machinery and allows escape from host surveillance and antimicrobial defenses.

Question 6

How are bacteria classified?

Answer 6

staining (Gram positive/negative), size, shape, color, respiration and reproduction. Subspecies are classified based on immunological data (serogroup or subtype) and biochemical properties (biotypes, strains, groups) or based on toxins or antibiotic sensitivities.

Question 7

What are the equivalent categories of subspecies of viruses?

Answer 7

serotypes, strains, variants, isolates

Question 8

How are viruses classified?

Answer 8

nucleic acid present, arrangement of nucleic acid, presence/absence of external envelope, symmetry

Question 9

Describe an advantage and disadvantage of life as a extracellular pathogen

Answer 9

Extracellular pathogens can grow and reproduce freely, and may move extensively within the tissues of the body. However, they are continuously exposed to the host’s immune defense mechanisms