- A disease that can be transmitted to humans from animals

Transmission of infection Flashcards by Georgie French

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

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What is meant by the word ‘virulence’?

The ability of a microbe to cause disease

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In relation to the infectious agent, What is meant by the word ‘dose’?

The number of microbes entering the body

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Virulence factors include exotoxins and endotoxins. What are 2 examples of exotoxins?

P. gingivalis (protease)

- S. aureus (enterotoxin & Leukocidin)

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Virulence factors include exotoxins and endotoxins. What is an example if an endotoxin?

Lipopolysaccharides (P. gingivalis & E. coli)

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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)

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What is the infectious dose of TB?

1 bacillus

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What is the infectious dose of Syphilis?

57 bacteria (ID50)

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What is the infectious dose of E. coli 0157?

<10 cfu

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What is the infectious dose of the influenza virus?

<10 (tissue culture ID50)

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Microbes are ubiquitous in nature. What does this mean?

They are found everywhere

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Where do most pathogenic microbes that infect humans come from?

Other humans

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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

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What is Zoonoses?

A disease that can be transmitted to humans from animals

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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

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What does prodrome mean?

An early symptom indicating the onset of a disease

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What is an incubation period?

The time between contamination and the development of symptoms
Varies widely for different infections

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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

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What is an example of a disease that has asymptomatic carriers?

Carriage of blood-borne viruses, e.g. HIV

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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

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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)