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Flashcards in Transmission of Infection Deck (41)
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what are the basic principles of the chain of infection?

- Infectious agent
- Reservoirs
- Portal of exit
- Means of transmission
- Portal of entry
- Susceptible host


what does virulence mean?

ability of the microbe to cause disease


what does dose mean?

number of microbes entering the body


what factors are included with regards to virulence?

• Exotoxins
○ P.gingivalis (protease)
○ S.aureus (endotoxin & leukocidin)

• Endotoxins
○ Lipopolysaccharide
(P.gingivalis & E.coli)


dont know how to question this / how to understand it but here we are to learn x

infectious dose:
Usually expressed as infectious dose 50 (ID50)
• TB = 1 bacillus
• Syphilis = 57 bacteria (ID50)
• E.coli 0157 = <10 cfu
•Influenza virus = <10 (tissue culture ID50)


name reservoirs where microbes can live

- humans
- animals
- fomites
- environmental


where does most pathogenic microbes that infect humans come from?

other humans


give an example of a human pathogen that comes from animals



give an example of a human pathogen that originates in the environment

clostridium tetani spores in soil


what are fomites

Contaminated objects or surfaces
Usually act as a bridge between health care workers and patients
Eg phone, keyboard, medical equipment surfaces, house keeping surfaces


what are the different sources of infection?

> patients in the acute phase of an infection = easily recognised eg influenza, common cold

> patients in the podromal phase of an infection = not easily recognised eg measles, mumps, chickenpox

> healthy carriers of pathogenic organisms = not easily recognised includes convalescent carriers and asymptomatic carriers eg HIV, Hep B and C, herpes viruses


what is the incubation period

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


what is the problem with longer incubation periods

longer time periods when the infecting microbe may be spread to others
means a greater spread of the disease because of more human contact


define asymptomatic carrier

an infected person with no clinical evidence of disease, though signs and symptoms of the disease may have been evident earlier


why are carriers dangerous in the spread of diseases

they are usually unaware of their infectious state


define colonisation

is the presence of bacteria on a body surface (like on the skin, mouth, intestines etc) with growth and multiplication without causing disease (clinical expression of the infection) in the person


define infection

the invasion of a host organism's bodily tissues by disease causing organisms


define exogenous

growing or originating outside an organism
caused by microbes from external soruces eg influenza


define endogenous

growing or originating within an organism
caused by members of the normal flora if
- flora becomes ecologically harmful due to population / gene expression shifts eg periodontal disease, dental caries
- they become displaced to another body site or are allowed to invade deeper tissues eg post surgical infections


explain portal of exit

microbes must escape from the source to colonise a new host


what are the different modes of escape (portal of exit)

- coughing
- sneezing
- tears
- urine

- blood donation
- dental handpiece aerosols


classify pathogens in the 4 hazard groups

- ability to cause infection
- severity of the disease that may result
- risk of population spread
- vaccine and treatment availability
(venn diagram - where these 4 things over lap = extremes = ebola outbreak)


what is R0

the number of cases one case generates on average over the course of its infectious period


explain R0 < 1

infection will die out in the long run


explain R0 > 1

infection will be able to spread in a population
higher R0 number = bigger the risk there is of an infection


what factors affect R0

- duration of infectivity
- infectiousness
- number of susceptible people


what is influenza

infectious agent
RNA virus with segmented genome
3 types = A, B, C
types A and B cause major outbreaks
> X2 surface glycoproteins
- hemaglutinin H1-15
- neuraminidase N1-9


what is pathophysiology

the disordered physiological processes associated with disease or injury


what is the pathophysiology of the influenza virus

infection of upper and lower respirator tract
release of cytokines (IF and TNF) = fever, headache, fatigue


explain the infection of influenza

- fever
- cough
- headaches
- fatigue

- bacterial pneumonia
- ear and sinus infections
- worsening of chronic medical conditions like asthma and heart disease