Vectors and Disease Virulence

David P. Clark

Virulence may increase when a vector carries a disease. If a germ hitches a ride from one victim to another via mosquito, it matters little that the first victim is too sick to move. Indeed, this may even work to the germ’s advantage. Mosquitoes will be able to land and suck blood without the victim swatting them. Diseases that are carried from person to person by some other agency have little motivation to evolve mildness toward humans. Rather, they must avoid disabling their carriers. What happens to the human victims is less important. Malaria, sleeping sickness, typhus fever, yellow fever, and many other diseases are spread by insects, ticks, or lice. These diseases are dangerous and show few signs ...