Session 8: Preventing Infections Flashcards
(35 cards)
Give examples of how transmissible infections can transmit.
From a non-human source to humans (common source) From person to person directly From person to person indirectly via a vector
Give example of common sources of transmission of infection.
Environmental source Food/water Animals
Give an example of an environmental source.
Legionella pneumophila
Give an example of a food/water source
Salmonella Salmonella typhoid is also transmissible from person to person
Give an example of an animal source
This is also called zoonotic and rabies is one.
Give examples of direct transmission from person to person.
Influenza Norovirus (winter vomiting disease) Neisseria gonorrhoea HIV Chlamydia
Give examples of indirect transmission from person to person.
Malaria with the help of mosquitos.
Define endemic disease.
Usual background rate of disease
Define outbreak.
Two or more cases of a single disease and single strain of that disease in time and place.
Define epidemic.
A rate of infection greater than the usual background rate. Epidemic > Endemic
Define pandemic.
A very high rate of infection spreading across many regions, countries and continents.
Define basic reproduction number (R0).
The average number of cases one case generates over the course of its infectious period, in an otherwise uninfected, non-immune population.
What does R0 > 1 mean?
That there is an increase in cases. One case generates more than an additional case. It is not linear.
What does R0 = 1 mean?
A stable number of cases.
What does R0 < 1 mean?
There is a decrease in cases.
Give examples of diseases with a high R0 vs. low R0.
High: measles (12-18), pertussis (12-17) Low: Sars (2-5), Influenza (2-3)
Give reasons for outbreaks, epidemics and pandemics.
A new pathogen An old pathogen with new antigens. New hosts New practice
How could an old pathogen get new antigens?
There are two main sorts: Antigenic shift and antigenic drift.
Explain antigenic shift.
If a person has two strains of influenza (e.g.) at the same time you might end up with a new novel strain of influenza which can spread. It is rare but it can happen. This is a fast change.
Explain antigenic drift.
Mutation of the pathogen. This is a slow change.
What is more detrimental? Antigenic shift or antigenic drift?
Antigenic shift is more hazardous because it is a fast change and it means that everyone will be susceptible. Like the swine-flu. This causes a higher susceptibility to outbreak, epidemic and pandemic. In the case of antigenic drift it is a slow progression of change which means there is less susceptibility.
Explain how a new host could cause outbreak.
A new host like babies after the antibodies from the mother disappeared or in immunosuppressed which receive bone marrow transplants they won’t have any native immune system ready to act. This can cause new outbreaks.
Explain how a new practice could cause outbreak.
A social change like in 1980s San Francisco where homosexuality became accepted. A paradigm shift where gay sex became more common lead to an increase in HIV transmission. Health care changes like blood products (transfusions) where money was an incentive to make people donate blood. Mostly IVDUs started donating blood in order to get more money for their addiction. Since there was no screening of HIV at the time this lead to even more transmission of HIV among people.
Define infectious dose. Give factors influencing infectious dose.
Number of micro-organisms required to cause an infection. Varies by: Microorganism Presentation of microorganism Immunity of potential host E.g. Salmonella has a high infectious dose over 10^5 of organisms needed to cause an infection. E. coli has a low infectious dose where less than 10 organisms needed to cause infection.
