Lecture 1 - What Is An Infection Flashcards
What is an infection?
The invasion of a hosts tissues by microorganisms
How is a disease caused by an infection?
Microbes INVADE
MULTIPLY
TOXINS produced
Host responds
How do people get infections?
Microorganisms from self
Infected by others
Infected by vector organisms
What are Microbiota/commensals (commensile microorganisms)?
Microbes that normally reside on or in the body that dont normally cause harm
How can commensals/Microbiota causes damage to a patient?
If they are transferred from other sites in the body (faecal-oral transmission)
Where do Microbiota usually reside?
On skin
On mucosal membranes
What are the 2 modes of transmission?
Horizontal transmission
Vertical transmission
What are the 3 methods of horizontal transmission?
-Contact
-Inhalation
-Ingestion (faecal-oral transmission most common)
How can infections be spread via contact?
What are the 3 types of ways they can be spread?
Directly (skin to skin, kissing, sexual intercourse)
Indirect (contaminated surfaces)
Vectors (mosquito for malaria)
How are infections spread via inhalation?
Water droplets in the air
Aerosols
What is vertical transmission of infections?
When an infection is passed from mother to child
This can be before birth or after birth
What is an example of a group of microorganisms which can be vertically transmitted and what diseases can it causes?
Group B streptococcus
Meningitis
Sepsis
Pneumonia
What is the process to microorganisms causing disease?
Host exposed to microorganism
Adherence (mucosal membranes or blood vessels)
Invasion (invades cells or between cells)
Multiplication
Dissemination (spreads e.g into bloodstream)
Virulence factors produced
Host cells damaged
What are virulence factors?
Substances produced by the microorganism that enhance its survival in the host
Like toxins
What causes the symptoms in an infection?
Host cell damage
How do host cells get damaged in infection?
Directly by toxins produced or cells bursting
Consequent to hosts immune response
What are the 2 disease determinants?
Pathogen
Patient
What about a pathogen determines the significance of the disease it causes?
Virulence factors produced
Inoculum size (amount person infected with)
What about a patient determines the severity of a disease?
The site of infection
Co-morbidities (any pre existing conditions)
Generally what 4 questions do we need to ask about a patient relating to an infection?
Is there an infection?
Where is the infection?
What is the cause of the infection?
What is the best treatment?
What 3 things do we do when trying to determine what sort of infection a patient has?
History
Examination
Investigations
When taking a history for a suspected infection what are we trying to establish?
Symptoms:
-focal or systemic
-severity
-duration
Potential exposures (like travel to malarial countries)
When examining a patient with a suspected infection what are we looking for?
Any potential organ dysfunctions or anything that is not functioning normally
What are the 2 types of investigations done with a person who has a suspected infection?
Specific investigations
Supportive investigations
What is a specific investigation?
Investigation which is trying to identify the specific causative organism for the infection
What is a supportive investigation?
An investigation which suggests whether a patient has an infection or not
What are some examples of supportive investigations?
Full blood count (number of neutrophils or lymphocytes)
CRP levels
Blood chemistry (liver and kidney function tests)
Imaging (X-rays, MRIs, ultrasound)
Histopathology (examination of tissues)
What may an increased neutrophil count indicate?
Bacterial infection
What May an increased lymphocyte count indicate?
Viral infection
What does C-reactive protein indicate?
An acute phase protein indicating an inflammatory process is happening
What type of specific investigations can be done to determine causative bacteria?
Swabs
Microscopy (gram satins, viewing cells in CSF)
Culture
Antibiotic susceptibility
Antigen detection
Nucleic acid detection
What specific investigations can be done to determine causative virus?
Antigen detection
Antibody detection (produced by the patient)
Detecting viral nuclei acid (DNA or RNA)
What must viral RNA be converted into first before it is used in PCR?
(Not all viruses have rna)
DNA
