Session 1 Lectures - Introduction to infection Flashcards
What is an infection?
two parts to definition
Invasion of a host’s tissues by micro-organisms AND a disease caused by microbial multiplication, sometimes toxins, and a host response (e.g. inflammatory response)
Why might symptoms of disease continue after microorganism killed by antibodies?
Because an inflammatory cascade has started
Give the 4 ways a person can be infected by their environment?
- Food
- Water
- Air
- Surface
What is a vector and give an example of one that causes infection?
A living carrier
Example: mosquito carrying malaria
What does the term endogenous source of infection mean?
A patients own microbial flora can move elsewhere in the body it is not suppose to be and cause infection
What are microbiota?
Microorganisms carried on the skin or mucosal surfaces
What is vertical transmission and give an example of this?
An infection passed from mother to child (either before or after birth)
Example: HIV - child often gets infected through breast milk
Give two ways in which the risk of passing on HIV from mother to child can be reduced
- Deliver by caesarean section
2. Mother does not breast feed
What are the 5 stages in which microorganisms cause disease?
- Exposure
- Adherence
- Invasion
- Multiplication
- Dissemination (spreading)
What is adherence?
Adhesin (part of bacterial cell surface) interacts with host cell receptor on cell surface allowing bacteria to attach
What are virulence factors and give two examples?
They are the properties of a microorganism that enable it to establish itself on a host and enhance potential to cause disease
Examples: endotoxins and exotoxins
What are endotoxins?
An endotoxin is a component of the bacterial wall that causes an inflammatory response in the host
What are exotoxins?
They are toxins secreted from the bacteria (also secreted during bacterial lysis)
Give 4 types of exotoxins
- A-B toxins (disrupt cell metabolism)
- Cytolytic (disrupts plasma membrane)
- Superantigens (results in large release of cytokines and leads to shock)
- Enzymes
What is the inoculum size of a microorganism?
The amount of the microorganism needed for a person to become infected
What are supportive investigations?
Investigations that look at how well the patient is
Give 5 types of supportive investigations
- Full blood count (look at levels of WBCs)
- C reactive protein (increases during inflammation)
- Liver and kidney function tests
- Imaging
- Histopathology (looking at tissue under microscope)
What are specific investigations?
Investigations that look to identify cause of infection
Give 4 types of specific investigations
- Specimen samples e.g. fluid
- M,C & S (microscopy, culture and antibiotic susceptibility)
- Antigen detection
- Nucleic acid detection (looking at DNA or RNA)
What are the 3 main approaches for identifying a virus?
- Antigen detection
- Antibody detection
- Detecting viral nucleic acid (DNA or RNA)
What is a tercian fever?
A fever that appears every 3 days
What are Koch’s postulates? List the 4.
Ways of thinking about demonstrating cause of infectious disease
- Microorganism must be found in all organisms with disease and not in healthy people
- Microorganism must be isolated and grown in culture
- Cultured microorganism should cause disease when inserted into healthy person
- The microorganism should be isolated from this host and matched to original cause
