S7) Infection Prevention Flashcards
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
