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MICR2209 > 1 - Host / Parasite interactions > Flashcards

1 - Host / Parasite interactions Flashcards

1
Q

What is an infectious disease

A

Any change from a state of health in which part or all of the host’s body cannot carry on its normal functions.

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2
Q

Parasitism

A

Symbiotic interaction between two organisms in which one benefits at the expense of the other

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3
Q

Characteristics of parasites

A
  • Live on or within host organism
  • Dependent on host
  • Parasite benefits whilst host is harmed
  • Typically cause disease
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4
Q

Infection (process)

A

The parasite grows and multiplies in or on its host

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5
Q

Infectious disease (outcome)

A

Where infection detrimentally affects host function

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6
Q

Pathogen

A

Any organism causing an infectious disease

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7
Q

Types of pathogens

A

Primary pathogens and opportunistic pathogens

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8
Q

Primary pathogens

A

Cause infectious disease in healthy hosts

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9
Q

Opportunistic pathogens

A

Cause infectious disease in ‘comprised’ hosts (e.g. immunocompromised). May be a part of the normal microbiota

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10
Q

Pathogenicity

A

the ability to cause disease

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11
Q

Virulence

A

The degree or intensity of pathogenicity. Indicated by fatality rate or ability to damage host tissues

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12
Q

Latent state

A

Pathogen is present, but no symptoms are evident

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13
Q

Stages of the infectious disease process

A
  • Incubation period
  • Prodromal stage
  • Illness period
  • Convalescent period (or death)
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14
Q

Incubation period

A

Time from pathogen entry to development of signs and symptoms. Pathogen development but no clinical manifestations

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15
Q

Prodromal stage

A

Non specific clinical manifestations, may be contagious

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16
Q

Illness period

A
  • Disease is most severe
  • Characteristic signs and symptoms of illness
  • Immune response triggered
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17
Q

Convalescent period (or death)

A

Recovery, signs and symptoms decline.

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18
Q

Acute non persistent

A

Rapid and self limiting

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19
Q

Chronic

A

Persistent or long lasting

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20
Q

Chronic

A

Persistent or long lasting

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21
Q

Why is knowledge of incubation periods important

A

Aids diagnosis and tracing spread of disease outbreaks

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22
Q

Parts of the infection chain

A
  • Reservoir/source
  • Transmission
  • Infectious dose
  • Exposure and growth
  • Host susceptibility
  • Exiting the host
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23
Q

Source

A

Location from which pathogen is transmitted to host

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24
Q

Animate source

A

Humans, plants, animals (e.g common cold)

25
Q

Zoonosis

A

Disease of animals that can be transmitted to humans

26
Q

Inanimate source

A

Soil, water, food (e.g. hepatitis A)

27
Q

Reservoir

A

Natural environmental location where the pathogen is normally found. May or may not also be the source

28
Q

Types of transmission

A
  • Airborne
  • Contact
  • Vehicle
  • Vector-borne
  • Others: vertical (transplacental, congenital); iatrogenic (medical procedures)
29
Q

Airborne transmission

A
  • Water droplets (small particles that can remain airborne for long time and travel long distances)
  • Dust (many systemic fungal infections)
30
Q

Contact transmission

A

Person to person or animal to person

31
Q

Vehicle transmission

A

An inanimate ‘vehicle’ is a source that has become contaminated/transmits a pathogen

32
Q

Fomite

A

inanimate object or substance that is capable of transmitting infectious organisms

33
Q

Vector tranmission

A

Vectors house infectious agents and transmit them one host to another, commonly
acting as a host itself (e.g. mosquito, ticks, fleas)

34
Q

External transmission

A
  • Passive carriage of pathogen on body of vector
  • No growth of pathogen during transmission
35
Q

Example of external transmission

A

Shigella dysenteriae: flies carry the bacterium on their feet from faecal sources to food

36
Q

Internal transmission

A

Pathogen carried within vector.

37
Q

Example of internal transmission

A

malarial parasite undergoes developmental changes in the mosquito vector

38
Q

Infectious dose 50 (ID50)

A

Number of organisms necessary to infect 50% of an experimental group of hosts in a specified time period. Varies with pathogen

39
Q

LD50

A

Number of pathogenic cells or amount of toxin required to kill 50% of infected individuals

40
Q

Is transmission alone enough for infection to occur

A

No. Specific cell surface receptors and appropriate conditions for growth must be present

41
Q

Extracellular pathogens

A

grow outside cells in blood and tissue fluids

42
Q

Intracellular pathogens

A

grow and multiply within cells

43
Q

Facultative intracellular pathogens

A

grow within or outside cells

44
Q

Obligate intracellular pathogens

A

only grow when inside cells

45
Q

Factors that effect host susceptibility

A

Genetic or constitutional factors, specific immunity and nonspecific factors

46
Q

Components of host defence mechanisms

A
  • Innate host resistance factors
  • adaptive immune mechanisms
47
Q

Exiting the host

A

Must occur if microbe is to be perpetuated. Can be active or passive escape

48
Q

Active escape

A
  • Movement of pathogen to portal of exit from host
  • Relatively uncommon (burrow out through the skin)
49
Q

Passive escape

A
  • Usual method
  • Excretion in faeces, urine, droplets, blood, saliva, or
    in host cells shed from the body
50
Q

What is virulence determined by

A

VIrulence factors. Can involve physical and chemical characteristics. Determine the degree to which the pathogen causes damage

51
Q

4 Virulence factors

A
  • adherence and colonisation
  • invasion
  • avoiding/resisting host defences
  • Damage to the host
52
Q

Adherence and colonisation

A

Help microbes to attach to host tissue (e.g. fimbriae/pili and capsules, capsid spikes of viruses

53
Q

Adherences factors

A

Adhesins

54
Q

Colonised host

A

Host that has microbe attached and reproduction follows

55
Q

Invasion

A
  • Spread from initial site of infection
  • invasion mechanisms vary among pathogens
  • Pathogens can spread by producing chemicals that disrupt the host cell surface or induce uptake by host cell
56
Q

Examples of mechanisms of resisting host defences

A
  • Bacteria can produce a sticky capsule that coats the bacterium and prevents its capture by immune cells
  • Hepatitis B virus causes infected cells to produce ‘decoy’ proteins that confuse the immune system
57
Q

Toxin

A

A microbial product or component that injures another cell or organism

58
Q

Bacterial exotoxins

A

Secreted proteins (e.g. tetanus, cholera)

59
Q

Fungal mycotoxins

A

Secondary metabolites (inadvertent consumption of fungus-contaminated foods)

MICR2209 (26 decks)

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