Introduction to Infection

Question 1

Why do we need to know the cause of infection?

Answer 1

• need to be able to measure infection with the correct tests
• need to give the correct treatment
• need to know the appropriate biosecurity measures to stop it spreading
• need to know what vaccines will be effective
• need to understand the disease progression

Question 2

What is the definition of infection?

Answer 2

• colonisation of an individual by an infectious agent

Question 3

What is the definition of a disease?

Answer 3

• when normal bodily functions are impaired, reducing performance and leading to clinical signs

Question 4

What is a carrier?

Answer 4

• any animal that can spread the pathogen

Question 5

What is aetiology?

Answer 5

• the cause, or causes of a disease or condition
• not all disease have a single aetiology some have multiple

Question 6

What is an incubation period?

Answer 6

• the time period between infection and when clinical signs are observed
  can be a few days - months/years

Question 7

What is an infectious period?

Answer 7

• the time interval during which a host is infectious

Question 8

Why is incubation period important?

Answer 8

• helps with diagnosis
• helps with treatment
• important for biosecurity

Question 9

What are 4 ways we can categorise infectious agents?

Answer 9

• By size
• by location
• by evolutionary classification
• by transmission

Question 10

Size - what are microparasites?

Answer 10

• parasitic organisms you can see by the eye
• multicellular
• fleas, mites, ticks, worms (nematode, tapeworm, trematode)

Question 11

Microorganism lifestyles can be what?

Answer 11

• parasitic
• opportunistic
• mutualism/commensal
• symbiosis
• saprophyte

Question 12

Describe a parasitic lifestyle

Answer 12

• can cause a disease by themselves
• can infect healthy individuals
• commonly require a host to reproduce

Question 13

Describe a opportunistic lifestyle

Answer 13

• infection caused by an infectious agent due to an opportunity that has occurred allowing the infection to occur
• weakened immune system
• removal of a microbiome
• breached barrier
• current infection

Question 14

Describe a commensal/mutualism lifecycle

Answer 14

• a relationship where one or both benefit, but without detriment affect to either party
• commensals can become opportunistic

Question 15

Describe a symbiosis lifecycle

Answer 15

• a relationship where both organism benefit and are dependent on each other
• e.g., microbiome in cattle/ horse GI tract

Question 16

Describe a saprophyte lifecycle

Answer 16

• microorganism that lives on dead or decaying organic matter
• impact of saprophytic bacteria on post-mortems of animals

Question 17

How do we classify infectious agents by location?

Answer 17

• extracellular or intracellular
• localised or disseminated

Question 18

What can location be split into for parasitology?

Answer 18

• endoparasites (helminths, protozoans)
• ectoparasites (fleas, ticks, lice, mites, monogeneans)

Question 19

where are most ectoparasites found?

Answer 19

• skin

Question 20

where are most helminths found?

Answer 20

• alimentary
• cardiorespiratory

Question 21

where are most protozoan parasites found?

Answer 21

• blood-borne

Question 22

How can pathogens be divided based on evolution?

Answer 22

• organisms are either prokaryotic or eukaryote

Question 23

Why are viruses an exception to evolution categories?

Answer 23

• viruses are neither prokaryotic or eukaryote
• they don’t fully meet definition of an organism
• no virus can replicate independently

Question 24

What are prions and why don’t they fit into the evolution category?

Answer 24

• they don’t fit into prokaryote or eukaryote
• just proteins but transmissible
• can misfold host prion proteins
• cause Bovine Spongiform Encephalopathy

Question 25

What is a Eukaryotic cell?

Answer 25

• eukaryotic cells have a nucleus and other organelles that are surrounded by a membrane
• they are found in multicellular organisms

Question 26

What are the components of a eukaryote?

Answer 26

• plasma membrane
• cilia
• cytoplasm
• cytoskeleton
• centriole
• lysosomes
• peroxisome
• mitochondria
• ER
• Golgi apparatus
• nucleolus
• nucleus
• nuclear envelope
• ribosomes

Question 27

What is a prokaryotic cell?

Answer 27

• prokaryotic cells from single-celled organisms such as bacteria
• they do a membrane bound nucleus or organelles

Question 28

What are the components of a prokaryote?

Answer 28

• nucleoid area containing DNA
• capsule
• plasma membrane
• cytoplasm
• flagellum
• plasmid - small circles of DNA
• ribosomes

Question 29

Why does it matter whether an infectious agent is prokaryotic or eukaryotic?

Answer 29

• immune recognition varies between the two
• treatments are designed to interact with unique molecules in the pathogen
• different structures are found in prokaryotic/eukaryotic organisms

Question 30

What are Toll-like receptors?

Answer 30

• they are receptors in key immune cells that can recognise specific pathogen-associated molecular patterns (PAMPs)

Question 31

What routes do pathogen have to transmit?

Answer 31

• ingestion
• aerial transmission
• direct contact
• indirect contact - e.g., fomites
• inoculation - vector bone bites
• iatrogenic transmission - creates by doctor
• across placenta

Question 32

What can transmission be subdivided into what?

Answer 32

• Horizontal
• Vertical
• transmission can be both

Question 33

What is horizontal transmission?

Answer 33

• transmitted from any individual to another of the same generation

Question 34

what is vertical transmission?

Answer 34

• transmission from one generation to the next by infection of embryo/foetus/newborn by parent

Question 35

What is a direct lifecycle?

Answer 35

• a lifecycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector

Question 36

What is an indirect lifecycle?

Answer 36

• where one or more intermediate hosts are required