Page "Virulence" Paragraph 17

Short-sighted evolution suggests that the traits that increase reproduction rate and transmission to a new host will rise to high frequency within the pathogen population.

These traits include the ability to reproduce sooner, reproduce faster, reproduce in higher numbers, live longer, survive against antibodies, or survive in parts of the body the pathogen does not normally infiltrate.

These traits typically arise due to mutations, which occur more frequently in pathogen populations than in host populations, due to the pathogens ' rapid generation time and immense numbers.

After only a few generations, the mutations that enhance rapid reproduction or dispersal will increase in frequency.

The same mutations that enhance the reproduction and dispersal of the pathogen also enhance its virulence in the host, causing much harm ( disease and death ).

If the pathogen's virulence kills the host and interferes with its own transmission to a new host, virulence will be selected against.

But as long as transmission continues despite the virulence, virulent pathogens will have the advantage.

So, for example, virulence often increases within families, where transmission from one host to the next is likely, no matter how sick the host.

Similarly, in crowded conditions such as refugee camps, virulence tends to increase over time since new hosts cannot escape the likelihood of infection.