Quiz 4 (Lecture 16) Flashcards
What is virulence?
is the harm done to the host during the course of an infection
What is intrinsic virulence?
is the portion of damage done to the host that is caused by the pathogen rather than by the host response
Why are pathogens so virulent?
trade-off hypothesis
What is the trade-off hypothesis?
virulence can increase, if in the processing of killing its host, it sufficiently increases its chances of being transmitted
What is an example of the virulence-transmission tradeoff paradigm?
Myxoma virus in rabbits
Explain the myoxma virus in rabbits example.
- Myxoma virus is a member of the Poxvirus family and is transmitted by mosquitos, fleas, lice, ticks, and mites
- Caused myxomatosis, an acute disease with initial 100% mortality rate, in European rabbits
- introduced in Australia in 50s, evolved to be less virulent but still deadly
Which does selection favor in refence to parasites?
- reproduce more quickly within their hosts until the parasites begin to harm host that transmission fails
Lower virulence strains do…
worse in a single host, but better in the population as a whole
What does strictly vertical (parent to offspring) direct transmission selects for?
low virulence, eventually commensalism
What does strictly horizontal direct transmission selects for?
high virulence
What is the first prediction for virulence evolution?
directly transmitted diseases are less virulent than vector borne diseases
- vector borne is carrying disease to other hosts so pathogen can be more virulent
What is the second prediction for virulence evolution?
diarrheal diseases are highly virulent
- water acts in similar fashion as insect vector
- diseases w/ a higher frequency of waterborne transmission are more virulent
What does the trade-off hypothesis imply about human behavior?
that human behavior can affect the severity of human disease
- remove waterborne transmission to lower virulence
What does multiple infection select for?
increased virulence if the impact of the parasites on the host is through mortality
In the case of competition, what does a pathogen need to do to be transmitted?
the pathogen has to dominate the competition, but doing so damages the host (virulence increases)
If parasites have sub-lethal effects on their host and if these effects reduce their rate of development, what will happen?
then multiplicity of infection generally leads to lower virulence
The more host species a pathogen regular infects, leads to what?
the pathogen to be less well adapted to any one of them
A pathogen that evolves to be good at exploiting one host loses what?
loses efficiency on other hosts
How are vaccines produced?
through serial passage
What is serial passage?
microbiologist use serial passage to study pathogen virulence and to produce live attenuated vaccines
- works b/c pathogens evolve rapidly
- made polio deadly in monkey but then wasn’t harmful to humans (how polio vaccine was made)
Some of the most virulent human diseases are caused by?
pathogens that spend most of their time in other hosts
- kill humans too rapidly to transmit effectively (ex ebola)
Childhood vaccines are what kind of vaccines?
sterilizing and protect nearly perfectly
What kind of vaccine is used more frequently?
imperfect vaccine
What is an imperfect vaccine?
vaccines that let the host survive but do not prevent the spread of pathogen
Why can imperfect vaccines cause increased virulence?
- extend host survival time allowing more virulent strains to transmit
- reduce the costs of virulence, thereby shifting the transmission-virulence trade-off
- allows unvaccinated host to experience disease worse
