8 - Activities of a pathogen 1 Flashcards
What do I need to know?
Bacterial disease and how bacteria CAUSE disease
Pathogen
A microbe capable of causing disease i.e. and infectious agent.
Infection
An infection is where the microbe is established in the host
Colonisation
Colonisation is infection with a microbe for a varying period of time. During colonisation there may or may NOT be an immune response
Infectious Disease
Interaction with a microbe that causes damage to the host. Infectious disease can cause symptoms or it may not
Endogenous
Infectious disease arises from colonising pathogen or flora
Exogenous
- 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
Zoonosis
Infectious disease is transmitted from another animal host
Where do most infectious diseases originate from
Most are endogenous and originate from within the body so have nothing to do with the external environment
Microbe
SUBmicroscopic, microscopic or macroscopic
What 3 things relate to infectious disease?
Host, pathogen/microbe, environment
What is an example of endogenous disease?
UTI - arises from bacteria already living in the urinary tract
What is a high risk / susceptible host
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
What could make a person susceptible to disease
- 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
Immunosenescence?
Immunosenescence is the state of immune deficiency caused by the immune system becoming relatively inactive in old age
Examples of exogenous
- 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
What is colonisation
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
Colonisation
‘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
What is a pathogen
A microbe that is capable to cause infectious disease
Primary pathogen
Isolation is always pathogenic (TB and gonorrhoea)
Principle pathogen
Isolation is USUALLY pathogenic and causes infection in otherwise well people with intact defences
Opportunistic Pathogen
Only causes infection when defences are down i.e. bacteria in soil
Where can infections occur
In the community or healthcare settings
Community onset infections
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
Healthcare associated infection
- 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
What is the single most important activity that you can do to prevent HAI
Wash hands
5 moments of hand hygiene
What must a microbe do to cause infection
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
Virulence factors?
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
2 ways a germ can cause disease
1 - interact and damage the cell
2 - evoke an immune response
What is the continuum of virulence
- Commensal bacteria that ‘never’ cause disease
- Commensal bacteria that rarely cause disease
- Requires some breech of host defences
- The capacity to cause disease in hosts with INTACT defences (highest virulence)
Describe the human flora?
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
Pyogenic infection
Tissue invasion, multiplication, immune response in a sterile site
Results in acute inflam/innate immune response and nphill phagocytosis
Granulomatous/Chronic infection
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
