Virus Evolution

Why is understanding virus evolution important?

Viruses infect every type of organism. Viruses are able to evolve very quickly. Understanding how viruses evolve is important to human health and agriculture.

Why can viruses evolve so rapidly?

Evolution acts on variation. A number of features in the biology of viruses cause allow them to be able to generate a lot of variation rapidly. Viruses have high mutation rates, produce numerous offspring and have short generation times. In addition recombination and re-assortment can also produce more variation.

What does virus fitness mean?

What one means by virus fitness depends on the context. There are two ways in which to think about virus evolution: within host evolution and between host evolution. Fitness refers to some-thing's ability to reproduce itself. If we are concerned with within host evolution we usually want to look at some measure of how quickly a virus can make copies of itself. If we are concerned with between host evolution; it is more appropriate to look at the number of new hosts can be infected by a host infected with a particular strain of virus.

Why do different viruses cause different amounts of harm to their hosts?

Virulence or the harm a virus inflicts on its host is dependent on a number of factors. The way in which the virus is transmitted has a large effect on the level of virulence that will evolve. Viruses that spread mostly by vertical transmission (transmission to offspring of the host) will usually evolve lower levels of virulence than those which are transmitted horizontally. Virulence may also depend on the relationship between virulence and the virus’s ability to rapidly spread. Lower virulence can also favored when viruses within a host are more closely related.

How did viruses originate?

Viruses don't leave a fossil record, so it is difficult to determine the origin of viruses. However there are three hypotheses as to how viruses originated. One hypothesis is that they evolved with other forms of life at the beginning or life. Another hypothesis is that they evolved from components of cells that gained the ability to replicate and spread to other cells. The third hypothesis is that viruses evolved from other inter-cellular parasites.



Bryan Roosien

PhD Canidate

School of Biological Sciences

Washington State University