Foundations

Question 1

Koch demosntrated that anthrax and TB were caused by specific bacterium

what were Koch’s postulates regarding criteria of an infection

Answer 1

• The organism must be regularly associated with the disease and its characteristic lesions.
• The organism must be isolated from the diseased host and grown in culture.
• The disease must be reproduced when a pure culture of the organism is introduced into a healthy, susceptible host.
• The same organism must be reisolated from the experimentally infected host (Box 1.4).

Does not cover all infections, such as malaria/ viruses, which cannot grow in culture

Question 2

What is a lysogen?

What is a prophage?

What is a provirus?

Answer 2

Some bacterial viruses can enter into either destructive (lytic) or relatively benign (lysogenic) relationships with their host cells.
Such bacteriophages were called temperate.

lysogen - viral genetic information persists in bacteria, but expression reduced. Controlled by repressor genes. Can reactivate when required

prophage - the specific name given to quiescent vial genome, in a lysogen

provirus - an integrated DNA copy of a retroviral genome in an animal genome is termed a provirus (DNA version of a prophage)

Question 3

What is an episome?

Answer 3

An episome is an exogenous genetic element that is not necessary for cell survival.

a genetic element inside some bacterial cells, especially the DNA of some bacteriophages, that can replicate independently of the host and also in association with a chromosome with which it becomes integrated

similar to a plasmid, except episome can integrate into host chromosome

Question 4

What are smaller than viruses?

Answer 4

viroids - which are infectious agents of a variety of economically important plants, comprise a single small
molecule of noncoding RNA,

prions - are thought to be single protein molecules

Question 5

What four characteristics are viruses classified by?

Answer 5

1. Nature of the nucleic acid in the virion ( DNA or RNA )
2. Symmetry of the protein shell ( capsid )
3. Presence or absence of a lipid membrane ( envelope )
4. Dimensions of the virion and capsid

Question 6

What is a satellite virus?

Answer 6

Satellites are composed of nucleic acid molecules that depend for their multiplication on coinfection of a
host cell with a helper virus. However, they are not related to this helper. When a satellite encodes the coat protein in which its nucleic acid is encapsidated, it is referred to as a satellite virus (e.g., hepatitis delta virus is a satellite virus).

Question 7

Where do virus names originate from

Answer 7

Associated disease – e.g rabies
Organ affected – hepatitis C
Geographic location of discovery – Ebola
Scientist who discovered it- Epstein-Barr
How it was thought to be transmitted – malaria “bad air”

Question 8

What is the Bradford-Hill criteria used for?

Answer 8

To establish a relationship between presumed cause and effect

Question 9

What are the 9 parts of the Bradford-Hill criteria?

Answer 9

Plausibility - biological rationale for relationship

Temporality - cause precedes outcome

Strength - A small association does not mean that there is not a causal effect, though the larger the association, the more likely that it is causal.

Biological gradient - higher dose means higher risk

Coherence - relationship consistent with previous knowledge

Consistency - The association is consistent when results are replicated with different people under different circumstances and with different measurement instruments

Specificity - single cause for single effect

Experiment - Any related research that is based on experiments will make a causal inference more plausible.

Analogy - Sometimes a commonly accepted phenomenon in one area can be applied to another area