Transmission of infection Flashcards
What are the 6 features of the chain of infection?
- Infectious agent
- Reservoir’s
- Portal of exit
- Means of transmission
- Portal of entry
- Susceptible host
What is meant by the word ‘virulence’?
- The ability of a microbe to cause disease
In relation to the infectious agent, What is meant by the word ‘dose’?
- The number of microbes entering the body
Virulence factors include exotoxins and endotoxins. What are 2 examples of exotoxins?
- P. gingivalis (protease)
- S. aureus (enterotoxin & Leukocidin)
Virulence factors include exotoxins and endotoxins. What is an example if an endotoxin?
- Lipopolysaccharides (P. gingivalis & E. coli)
What is the infectious dose of an infectious agent usually expressed as?
- Usually expressed as infectious dose 50 (ID50 - the dose you can get a 50% effect in the test species)
What is the infectious dose of TB?
- 1 bacillus
What is the infectious dose of Syphilis?
- 57 bacteria (ID50)
What is the infectious dose of E. coli 0157?
<10 cfu
What is the infectious dose of the influenza virus?
<10 (tissue culture ID50)
Microbes are ubiquitous in nature. What does this mean?
- They are found everywhere
Where do most pathogenic microbes that infect humans come from?
- Other humans
Most pathogenic microbes that infect humans come from other humans, but where else can they come from? (3 points)
- Animals: Some human pathogens come from animals (zoonoses) e.g. anthrax
- Environment: Some human pathogens originate from the environment e.g. Clostridium tetani spores in soil
- Fomites: contaminated objects or surfaces
What is Zoonoses?
- A disease that can be transmitted to humans from animals
Sometimes microbes can be transmitted to humans by fomites (contaminated objects or surfaces). What 2 categories can this be divided into?
- Medical equipment surfaces
- House keeping surfaces
What does prodrome mean?
An early symptom indicating the onset of a disease
What is an incubation period?
- The time between contamination and the development of symptoms
- Varies widely for different infections
What do longer incubation periods of diseases permit? (2 points)
- Longer time periods when the infecting microbe may spread to others
- Greater spread of disease because of more human contact
What is an example of a disease that has asymptomatic carriers?
- Carriage of blood-borne viruses, e.g. HIV
What Is meant by colonisation?
The presence of micro-organism(S) in or on a host, with the growth and multiplication, but without any overt clinical expression (infection) at the time the micro-organism is isolated
What is an endogenous reservoir?
- From body’s own flora
What is an asymptomatic carrier of a disease?
- An infected person with no clinical evidence of disease, though signs and symptoms of the disease may have been evident earlier
- Carriers as well as their contacts are usually not aware of their infectious state
What is an exogenous reservoir?
- From external flora that is usually acquired by transmission of infection
- Diseases caused by microbes from external sources e.g. influenza
When can an endogenous reservoir be infectious? (2 points)
- If flora become ecologically harmful due to population/gene expression shifts e.g. periodontal disease and dental caries
- If they become displaced to another body site or are allowed to invade deeper tissues e.g. post surgical infections
Microbes must escape from the source to colonise a new host. Mechanisms of escape vary depending upon the source. What are the 2 ways the mode of escape can be?
- Natural (e.g. coughing or sneezing)
- Artificial (e.g. blood donation or dental handpiece aerosols)
Give a few examples of hoe microbes can escape from the body? (13 possible points)
- Tears
- Nasal secretions
- Saliva
- Blood in saliva
- Respiratory fluids and sputum
- Blood and tissue fluids exiting through small breaks in the skin or through injuries
- Contact with the skin
- Breast milk
- Faeces
- Intestinal fluids
- Semen
- Vaginal secretions
- Urine
COSHH classifies human pathogens into 4 hazard groups based on what 4 things?
- The ability to cause infection
- The severity of the disease that may result
- The vaccine and treatment available
- The risk of population spread
What is meant by ‘R0’ (R naught)?
- The number of cases one case generates on average over the course of its infectious period
When R0 (R naught) <1, What does this mean?
- The infection will dies out in the long run
When R0 (R naught) >1, What does this mean?
The infection will be able to spread in a population
What are the factors that can affect R0 (R naught)? (3 points)
- Duration if infectivity
- Infectiousness
- Number of susceptible people
How many types of (influenza) RNA viruses have segmented genomes?
- Three types: A, B & C
What kind of outbreak can occur with Type A and B influenzas and what are the 2 surface proteins?
- Major outbreaks
2 surface proteins:
- Haemaglutinin H1-15
- Neuraminidase N1-9
What is pathophysiology?
- The disordered physiological processes associated with disease or injury
What does infection of the upper respiratory tract and the lower respiratory tract cells equal?
Respiratory tract symptoms
What are common symptoms of a mild (uncomplicated) form of influenza? (4 points)
- Fever
- Cough
- Headaches
- Fatigue
What are common symptoms of a severe (complicated) form of influenza? (3 points)
- Bacterial pneumonia
- Ear & sinus infections
- Worsening of chronic medical conditions (asthma, heart disease)
What is the incubation period for influenza?
- 2-3 days
When is someone with the influenza virus infectious?
- Once symptoms appear
Where does the influenza virus shed from?
Shed in upper respiratory tract secretions
Once a person is infectious with influenza, how long a re they infectious for?
- 3-5 days
- Children are infected for longer
How long can influenza A & B survive on steel and plastic?
24-48 hours
Hoe long can influenza A & B survive on cloth, paper and tissues?
- For <8-12 hours
For how long can transmission of a virus occur from steel to hands?
Over 24 hours
For how long can transmission of a virus occur from paper tissue to hands?
For 15 minutes
How long will a virus survive on hands for transmission?
- Approx 5 mins
What are 4 ways that viruses can enter the body?
- Respiration (aerosols)
- Inhalation (all particles)
- Direct contact (droplets )
- Indirect contact (settled particles - face touching)
What are 4 examples of patients that are at particularly high risk of complicated infections of influenza?
- Elderly
- Young children
- Pregnancy
- Chronic medical conditions (diabetes, asthma, heart disease)
How much more likely are patients with health conditions likely to die from the flu?
- 18x more likely
The flu vaccination is offered to children as kids are more infectious for longer periods of time and tent to act as a reservoir. What children is the vaccine offered to and what is the vaccine?
- Children aged 2-5
- Primary school aged children
- Nasal spray (live attenuated virus)
