Virulence Flashcards
What is virulence?
virulence - additional host mortality caused by pathogen
Virulence in mathematical models vs in reality
quantified in mathematical models as infection-induced increase in host mortality rate or reduction in host reproductive rate, in theory refers to instantaneous mortality rate caused by infection
Virulence in experimental data
measured in experimental data - quantified as “harm” done to host: host anemia, weight loss, morbidity (assuming that this harm is correlated with host fitness)
What is the result of evolution being subject to functional constrains in the sense of virulence?
- pathogens maximize their fitness
- evolution is subject to functional constraints and thus subject to life history trade-offs
- for example: increased pathogen transmission rate requires more intense host exploitation causing greater host mortality
What is the formula for R0 when you need to count in virulence>?
See notes
What is the story with Australia the British and rabbits?
- they put rabbits in Australia british people have something to hunt but them the rabbits got out of control
- they introduced a virus (Proxiviridae) to kill the rabbits and the different strains of the virus have very specific effects on mortality of the rabbits
Why are the averagely virulent strains the most effective?
you need to have balance - your host needs to be walking around for long enough but the infection also needs to be aggressive enough to make it spreadable
How did the rabbits react to the virus?
- rabbits evolve too!
- rabbit population dropped from 600k to 100k but then went back up to 300k
- in 1991 a calcivirus causing rabbit hemorrhagic fever was released with more success. Current bouncing back!
what are the predictions of the virulence theory?
there will evolve a medium level of virulence over time
what is the trade off when the pathogen specializes?
when a pathogen can infect multiple hosts specialisation towards a specific host can come at a cost of not being able to infect other hosts as effectively
What is a serial passage?
serial passage: - you transfer pathogen from the host to the next host (usually genetically identical) at the peak of its growth so from the pathogen’s point of view it is constantly growing - leads to specialization of the pathogen; so for example it gets very good at infecting lab mice but not that good at infecting people
Is virulence higher or lower in pathogens with mode of transmission different than direct transmission ?
virulence will be higher in parasites with transmission mode other than direct transmission (vectors or environmental) - if a parasite does not rely on direct contact or transmission it will not pay the fitness cost for increasing host mortality
What is the virulence in vertical transmission?
in vertical transmission (between generations) the virulence tends to be lower as the pathogen needs the host to stay alive long enough to pass it to the next generation (for example mother to child)
What is the virulence in environmental transmission?
you tend to have higher virulence in environmental transmission - if the pathogen can persist in the environment it can kill off hosts much quicker and not feel then just persist in the environment
What is the virulence in VBD?
VBD should be able to have higher virulence and that’s because they spend time not just in the host but also in the vector so if they kill their hosts quickly but not so quickly that the vector can still contact them then they should be fine (not good data to support this)
