ToB: Infectious Diseases

Question 1

What is the purpose of Koch’s Postulates and what are they?

Answer 1

Criteria to identify the causative agent of a disease:

1. The same pathogen must appear in every case of disease
2. Pathogen must be able to grow in pure culture
3. Pathogen must be isolated in pure culture and cause same symptoms as expected
4. If the pathogen is taken out of an inoculated organism it should be the same pathogen

Question 2

Name 4 exceptions to Koch’s Postulates

Answer 2

1. some pathogens can’t be grown in pure culture
2. some pathogens cause multiple diseases
3. some diseases cause multiple pathogens
4. some diseases only cause diseases in humans

Question 3

Which myeloid cell directly combats macro parasites?

Answer 3

Eosinophils

Question 4

What are the 3 ways infectious diseases are classified?

Answer 4

1. Clinically: based on signs and symptoms
2. Epidemiologically: based on the reservoir
3. Microbiologically: identifying the causative agent

Question 5

Name 3 macroparasites

Answer 5

platyhelminths, nematodes and arthropods

Question 6

Why are prions hard to detect/eliminate?

Which disease is associated with prions?

Answer 6

They are heat, radiation and disinfectant resistant.
Hard to detect: They are slow replicating and have a long incubation period, and therefore lie dormant for a long time and when you’re infected you don’t elicit an immediate immune response

Creutz-Jacob disease: prions trigger proteins in the brain to fold abnormally

Question 7

Name the 5 steps of the lytic viral cycle

Answer 7

1. attachment
2. penetration
3. synthesis of viral nucleic acids and proteins
4. packaging and assembly
5. release and cell lysis

Question 8

What is the Baltimore classification for?

Answer 8

Classifying viruses based on genome, envelope, shape, etc.

Question 9

Name two methods to identify bacteria and which diseases can be identified with the “less common” method

Answer 9

Acid-fast stain: cheaper but more insensitive, can be used for mycobacteria in leprosy

Gram Staining:

Question 10

Identify the structural differences in (+) and (-) gram cell walls of bacteria

Answer 10

Gram (+) cell walls: Have a much thicker peptidoglycan layer
Gram (-) cell walls: have a lipopolysaccharide layer that protects against the immune system and chemotherapeutic agents

Question 11

Name the 3 steps in gram staining

Answer 11

1. Add crystal violet stain which binds to the peptidoglycan layer of (+) and (-) bacteria
2. Add alcohol which washes away the stain, the (-) peptidoglycan layer is so thin it should wash away and appear clear, the (+) bacteria should still be purple
3. Pink Counterstain: (-) is now blue, and (+) is now pink

Question 12

What makes the microbiome opportunistic?

Answer 12

Our microflora/gut bacteria begin unharmful but have the potential to become harmful following a mutation, microbiome differences are linked to individual health issues

Question 13

Which bacterial structure looks like chains and which structures can they form?

Answer 13

Streptococci can form external structures such as flagella, pilli, cell envelopes and capsules

Question 14

Which bacterial structure looks like rods and which structures can they form?

Answer 14

Bacilli can form internal structures like spores and inclusion granules

Question 15

Explain the relationship in pathogen-host in commensalism in comparison to mutualism

Answer 15

Commensalism is when the pathogen benefits with no harm to the host
Mutualism is when both benefit

Question 16

When are fungi infections more severe, how are they normally caused and name 2 common conditions
What characteristic of fungi protects them?

Answer 16

More severe if you’re already immunocompromised, normally caused by external environment or normal gut bacteria: athlete’s foot and ringworm

Thick chitin cell wall

Question 17

What are protozoa? How are they commonly contracted and name an example condition.
Name 3 pathogenic protozoa

Answer 17

Parasitic or free-living microparasites, mostly contractable through food or water: malaria
Sporozoa, flagellates and amoebas

Question 18

How do arthropods cause disease?

Answer 18

Directly by feeding and indirectly by transmitting

Question 19

Name 8 ways parasites can be transmitted

Answer 19

Air-borne, sexually, food and water, vector-borne, inoculation, orally, skin, trans-placental

Question 20

What is it meant by pathogenicity?

Answer 20

The propensity of an agent to cause disease/clinical symptoms

Question 21

What is the incubation period?

Answer 21

Period of time between exposure and onset of clinical symptoms/signs

Question 22

What is it meant by an inapparent/subclinical infection

Answer 22

An infection with no clinical signs/symptoms

Question 23

What is a bacteriophage and how does it reproduce?

Answer 23

A bacteriophage is a virus that infects bacteria. It uses the lysogenic cycle to replicate prophage (viral genetic info)

Question 24

Compare and contrast cellular content, DNA and replication differences in prokaryotes and eukaryotes

Answer 24

Prokaryotes are missing a distinct nucleus,
DNA is usually in a nucleoid but can have additional plasmids, transcription and translation can be carried out simultaneously

Eukaryotes have a distinct nucleus bound by a nuclear membrane, DNA is on several chromosomes, transcription and translation are separate, and they have membrane-bound organelles

Question 25

What ‘stage’ comes before and leads to infection?

Answer 25

Colonization/carriage transient phase: pathogen is inside body but no clinical signs/symptoms