8 - Activities of a pathogen 1

Question 1

What do I need to know?

Answer 1

Bacterial disease and how bacteria CAUSE disease

Question 2

Pathogen

Answer 2

A microbe capable of causing disease i.e. and infectious agent.

Question 3

Infection

Answer 3

An infection is where the microbe is established in the host

Question 4

Colonisation

Answer 4

Colonisation is infection with a microbe for a varying period of time. During colonisation there may or may NOT be an immune response

Question 5

Infectious Disease

Answer 5

Interaction with a microbe that causes damage to the host. Infectious disease can cause symptoms or it may not

Question 6

Endogenous

Answer 6

Infectious disease arises from colonising pathogen or flora

Question 7

Exogenous

Answer 7

• Infectious disease arises from elsewhere i.e. influenza is an exogenous cause of infectious disease as it is NOT living in the body
• includes human to human transmission and zoonosis and the environment

Question 8

Zoonosis

Answer 8

Infectious disease is transmitted from another animal host

Question 9

Where do most infectious diseases originate from

Answer 9

Most are endogenous and originate from within the body so have nothing to do with the external environment

Question 10

Microbe

Answer 10

SUBmicroscopic, microscopic or macroscopic

Question 11

What 3 things relate to infectious disease?

Answer 11

Host, pathogen/microbe, environment

Question 12

What is an example of endogenous disease?

Answer 12

UTI - arises from bacteria already living in the urinary tract

Question 13

What is a high risk / susceptible host

Answer 13

Someone that is currently not infected but is in a region of high prevalence or is at a high risk of being infected i.e. a healthy person living in an area with endemic malaria

Question 14

What could make a person susceptible to disease

Answer 14

• Other illnesses i.e. HIV/chronic lung disease ^ risk of respiratory infection as cilia are damaged
• risk behaviours such as unprotected sex
• immune deficiency (inborn or acquired - often treatments interfere with the IS. Age also causes inactivity of IS due to immunosenescence)
• other factors; often don’t know why

Question 15

Immunosenescence?

Answer 15

Immunosenescence is the state of immune deficiency caused by the immune system becoming relatively inactive in old age

Question 16

Examples of exogenous

Answer 16

• human to human (common)
• environ and zoonosis
  > both uncommon as the germs here don’t interact well with our cells and if they do our IS is usually effective against them

Question 17

What is colonisation

Answer 17

It is the process by which a foreign particle infects a host. It is similar to sub-clinical infection. Most often colonisation does not cause symptoms and so does not cause the host any trouble. Occasionally there is an immune response and so rarely colonisation becomes infectious (damages the host)
Staph aureus is an example of a bacteria that often colonises humans in the nasal cavity and does generally NTO cause any issues

Question 18

Colonisation

Answer 18

‘partly endogenous and partly exogenous)
When a microbe is not usually part of our flora but you will often find it in otherwise healthy people i..e no symptoms but there is an immune response. Colonisation occurs at various sites depending on the bacteria - staph aureus
Colonisation of bacterial helps prevent overgrowth of dangerous bacteria
We can also be colonised with bacteria that could harm us if they got into our blood/internal organs

Question 19

What is a pathogen

Answer 19

A microbe that is capable to cause infectious disease

Question 20

Primary pathogen

Answer 20

Isolation is always pathogenic (TB and gonorrhoea)

Question 21

Principle pathogen

Answer 21

Isolation is USUALLY pathogenic and causes infection in otherwise well people with intact defences

Question 22

Opportunistic Pathogen

Answer 22

Only causes infection when defences are down i.e. bacteria in soil

Question 23

Where can infections occur

Answer 23

In the community or healthcare settings

Question 24

Community onset infections

Answer 24

Community onset conditions are those easily transmitted like coughs, colds, influenza and there are generally annual episodes of certain community onset infections. Community onset infections are generally mild and don’t require treatment

Question 25

Healthcare associated infection

Answer 25

• Healthcare associated infection is a very common complication of healthcare. Lots of infectious disease occurs because of medical care
• 1/10 people in hospital develop an infection as a DIRECT result of the care they receive
• many are avoidable (not chemo related)
• kills people
• costs 300 million a year

Question 26

What is the single most important activity that you can do to prevent HAI

Answer 26

Wash hands

5 moments of hand hygiene

Question 27

What must a microbe do to cause infection

Answer 27

To cause infection an organism must possess an array of factors (virulence) that regulate the interaction with the host - often physical attachment to the host cell
To cause disease these virulence factors need to damage the host or stimulate a significant immune response

Question 28

Virulence factors?

Answer 28

Genetic determinants that allow a pathogen to cause disease i.e.
adherence
invasion
immune evasion
toxins
Virulence factors are essentially ways to attack human cells and avoid the IS.
Soil has low virulence

Question 29

2 ways a germ can cause disease

Answer 29

1 - interact and damage the cell

2 - evoke an immune response

Question 30

What is the continuum of virulence

Answer 30

1. Commensal bacteria that ‘never’ cause disease
2. Commensal bacteria that rarely cause disease
3. Requires some breech of host defences
4. The capacity to cause disease in hosts with INTACT defences (highest virulence)

Question 31

Describe the human flora?

Answer 31

Humans are covered in approx 5000 different species
1 quadrillion bacteria which mostly live in the gut - there are 10x more bacterial cells than human
The diversity of the flora varies at different body sites i.e. gut, skin
Disturbances in the human flora leads to DISEASE - diabetes, heart disease, alzeheimers, cancer, immune function, allergy
Flora maintain good health i.e. gut bacteria help ferment carbohydrates
Live comensally

Question 32

Pyogenic infection

Answer 32

Tissue invasion, multiplication, immune response in a sterile site
Results in acute inflam/innate immune response and nphill phagocytosis

Question 33

Granulomatous/Chronic infection

Answer 33

Is when the bacteria evades the innate immune system and so cellular immunity is required. Macrophages are activated and fuse and surround the antigen
Results in an incomplete host response and forms a granuloma
This occurs in TB and chronic inflam