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MICR2209 > 1 - Host / Parasite interactions > Flashcards

1 - Host / Parasite interactions Flashcards

(59 cards)

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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

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A

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

25
Zoonosis
Disease of animals that can be transmitted to humans
26
Inanimate source
Soil, water, food (e.g. hepatitis A)
27
Reservoir
Natural environmental location where the pathogen is normally found. May or may not also be the source
28
Types of transmission
- Airborne - Contact - Vehicle - Vector-borne - Others: vertical (transplacental, congenital); iatrogenic (medical procedures)
29
Airborne transmission
- Water droplets (small particles that can remain airborne for long time and travel long distances) - Dust (many systemic fungal infections)
30
Contact transmission
Person to person or animal to person
31
Vehicle transmission
An inanimate 'vehicle' is a source that has become contaminated/transmits a pathogen
32
Fomite
inanimate object or substance that is capable of transmitting infectious organisms
33
Vector tranmission
Vectors house infectious agents and transmit them one host to another, commonly acting as a host itself (e.g. mosquito, ticks, fleas)
34
External transmission
- Passive carriage of pathogen on body of vector - No growth of pathogen during transmission
35
Example of external transmission
Shigella dysenteriae: flies carry the bacterium on their feet from faecal sources to food
36
Internal transmission
Pathogen carried within vector.
37
Example of internal transmission
malarial parasite undergoes developmental changes in the mosquito vector
38
Infectious dose 50 (ID50)
Number of organisms necessary to infect 50% of an experimental group of hosts in a specified time period. Varies with pathogen
39
LD50
Number of pathogenic cells or amount of toxin required to kill 50% of infected individuals
40
Is transmission alone enough for infection to occur
No. Specific cell surface receptors and appropriate conditions for growth must be present
41
Extracellular pathogens
grow outside cells in blood and tissue fluids
42
Intracellular pathogens
grow and multiply within cells
43
Facultative intracellular pathogens
grow within or outside cells
44
Obligate intracellular pathogens
only grow when inside cells
45
Factors that effect host susceptibility
Genetic or constitutional factors, specific immunity and nonspecific factors
46
Components of host defence mechanisms
- Innate host resistance factors - adaptive immune mechanisms
47
Exiting the host
Must occur if microbe is to be perpetuated. Can be active or passive escape
48
Active escape
- Movement of pathogen to portal of exit from host - Relatively uncommon (burrow out through the skin)
49
Passive escape
- Usual method - Excretion in faeces, urine, droplets, blood, saliva, or in host cells shed from the body
50
What is virulence determined by
VIrulence factors. Can involve physical and chemical characteristics. Determine the degree to which the pathogen causes damage
51
4 Virulence factors
- adherence and colonisation - invasion - avoiding/resisting host defences - Damage to the host
52
Adherence and colonisation
Help microbes to attach to host tissue (e.g. fimbriae/pili and capsules, capsid spikes of viruses
53
Adherences factors
Adhesins
54
Colonised host
Host that has microbe attached and reproduction follows
55
Invasion
- 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
Examples of mechanisms of resisting host defences
- 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
Toxin
A microbial product or component that injures another cell or organism
58
Bacterial exotoxins
Secreted proteins (e.g. tetanus, cholera)
59
Fungal mycotoxins
Secondary metabolites (inadvertent consumption of fungus-contaminated foods)

MICR2209 (26 decks)

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