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Flashcards in S7) Infection Prevention Deck (19)
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How do viruses cause infections?

⇒ Encounter a host cell

⇒ Enter host cell

⇒ Undergo primary replication

⇒ Spread to a final target tissue

Infect and successfully replicate in a susceptible population of host cells


What causes the signs and symptoms seen in viral infections?

The signs and symptoms of viral disease are the culmination of a series of interactions between the virus and the host


Describe the underlying process in acute infections

Acute infections involve a virus undergoing multiple rounds of replication, resulting in the death of the host cell, which is used as a factory for virus production

E.g. poliovirus, influenza virus


Describe the underlying process occurring in latent infections

- Latent infections involve persisting viral DNA either as an extrachromosomal element / as an integrated sequence within the host genome

- During cell growth, the genome of the virus is replicated along with the chromosomes of the host cell 

E.g. herpes simplex virus type 1 (DNA viruses/retroviruses)


Describe the underlying process occurring in chronic infections

Chronic infection involves the continuous shedding of viral particles after the period of acute illness, sometimes without host cell death or overt cellular injury 

- They don't result in overt disease but produce disease after a prolonged interval and are associated with defective host immune responses 

E.g. hepatitis C virus → chronic hepatitis → liver cancer


Explain the three different ways in which infections can be transmitted 

- Infections are transmissible from a non-human source to humans e.g. food/water – food poisoning organisms, animals – rabies 

- Infections are transmissible from person to person directly e.g. norovirus, influenza, N.gonorrhoea

- Infections are transmissible from person to person indirectly (vector) e.g. mosquitoes – malaria 


In terms of infection transmission and prevention, define the following terms:

- Endemic disease

- Outbreak

- Endemic disease – the usual background rate

- Outbreak – two/more cases linked in time and place (plausible in terms of infection dynamics – incubation period, etc)


In terms of infection transmission and prevention, define the following terms:

- Epidemic

- Pandemic

- Epidemic – a rate of infection greater than the usual background rate

- Pandemic – very high rate of infection spreading across many regions, countries, continents


In terms of the influenza virus, distinguish between antigenic drift and antigenic shift

- Antigenic drift refers to the changes to the flu virus that happen slowly over time

- Antigenic shift refers to the event when two different flu strains combine to infect the same cell


What is basic reproduction number (R0) and what is its significance?

 R0 is the average number of cases one case generates over a course of its infectious period, in an otherwise uninfected, non-immune population:

- If R0 > 1 → increase in cases

- If R0 = 1 → stable number of cases

- If R0 < 1 → decrease in cases


Provide 3 reasons for outbreaks, epidemics and pandemics

- New pathogen (antigens, virulence factors, antibacterial resistance)

- New hosts (non-immunes, healthcare effects)

- New practice (social, healthcare)


What is infectious dose?

- Infectious dose is the number of micro-organisms required to cause infection

- It varies by the micro-organism, presentation of micro-organism and immunity of potential host



Outline infection prevention interventions in terms of the 4 P's


Outline infection prevention interventions in terms of pathogen

- Reduce/eradicate pathogen: antibacterials, decontamination, sterilisation  

- Reduce/eradicate vector: eliminate vector breeding sites 


Outline infection prevention interventions in terms of patient

- Improved health: nutrition, medical treatment 

- Immunity: passive e.g. maternal antibody, active e.g. vaccination


Outline infection prevention interventions in terms of practice

- Avoidance of pathogen or its vector

- Protective clothing, equipment: long sleeves & trousers against mosquito bites, PPE in hospitals 

- Behavioural: safe sex, food and drink preparation, safe disposal of sharps


Outline infection prevention interventions in terms of place

Environmental engineering:

- Safe water

- Safe air

- Good quality housing

- Well-designed healthcare facilities


Explain the good and bad consequences of infection prevention

- Good – decreased incidence or elimination of disease/organism e.g. smallpox, polio

- Bad:

I. Decreased exposure to pathogen → decreased immune stimulus → decreased antibody → increased susceptibles → outbreak

II. Later average age of exposure → increased severity


What is the Epstein-Barr virus?

EBV infection (aka infectious mononucleosis) is a viral latent infection which affects B lymphocytes and produces characteristic atypical lymphocytes that may be useful in the diagnosis of the disease