Infectious Disease Flashcards
How are infectious diseases parasites?
All living things of sufficient size suffer from parasites. Parasites reproduce faser than the host and therefore evolve faster. In one human lifespan there are approximately 1 million generations of bacteria. The immune systems ability for resistance is fixed at what we are born with but parasites evolve during our lifespan.
How do infectious diseases act as a selection pressure on humans?
In an epidemic the most susceptible people will succomb and die first. The people with the most resistance will survive and will be genetically different from the fatalities. The population has therefore changed from the epidemic.
What is virulence?
This is the speed at which parasites reproduce. High virulence is a rapid increase in population parasites. There is a tendency due to natural selection for virulence to increase.
What will happen if it is highly virulent?
The host will die quickly and become immobilised, and may become non-infectious. So there is a trade-off between virulence and time available to spread the disease.
What happens when there is a high concentration of people?
It is easily spread and virulence increases. If there is a lower concentration of people with less contactand fewer opportunities to spread then virulence has to reduce.
What is an example of a disease that was too virulent and became extinct?
Green monkey disease
What happens if the vector is resistant?
If the vector (animal host) is resistant then there can be extreme virulence but the disease survives because it is not lethal to the host population.
What helps produce infectious diseases?
Agriculture has led to zoonosis (diseases transmitted to humans from animals). International communication, migration and mixing in dense urban areas all produces infectious diseases.
