My motivation for this post
came from a great course I took, Ecology of Infectious Diseases. (In addition I
am trying to not to be a sluggard!) The theme of the course is: imagine you are
a microparasite (pathogen) that is willing to take every chance to survive.
This leads my interesting thoughts on a paper by B R. Levin et al.
In the section titled "Within-Host Population Dynamics of Pathogen
Proliferation", he wrote:
If the course of a microparasite infection in a vertebrate host
were described without jargon, the process would be readily recognized as one
of population dynamics and evolution.
...
This
perspective on pathogenesis and the immune response as ecological,
population-dynamical, and evolutionary processes has been well recognized for
some time (11). However, it has had little impact on contemporary research on
the mechanisms of pathogenesis. Much of this
research is qualitative rather than quantitative, and it can be
described as a quest to characterize (genetically, biochemically, and
physiologically) the interaction between infectious pathogens and the host's
immune defenses. Although this research provides an indispensable basis for
understanding pathogenesis and the host's response to infection, it tells only
a part of the story. A complete account of the
course of an infectious disease must include a quantitative description of the
major forces that determine the abundance, diversity, and distribution of a
pathogen population within an infected host and the immune defenses involved in
its control.
It is fascinating that the
author pointed out the same thing came to me when I learned human population
genetics. Why wouldn't we study viruses from a population biology point of
view?
For decades the virologists
characterized function of tremendous amount of viral proteins, host factors
interaction, by saying that "XXX protein interacts with XXX host factors,
which is increased/decreased during infection". These facts are important
but only "parts of the story". For some reasons would trust the
author as we always lose a global view in biomedical research.
Viruses could be great source
to study from population genetics of view, if we think the genome of every
virus as the haplotype of every individuals. Some alleles in the viral genome
confers "susceptibility" to the host, that is, loss of
pathogenicity/infectiousness. This sounds very familiar when an allele in human
was found causative of the susceptibility to a pathogen in a human
subpopulation.
Another way to think about
the viral population genetics is to refer the mosaicism of the organism. The
viruses with slightly different genome function as a whole parasite. These
minute mutations of each viral particle have a huge impact on the population
level. This sounds like the quasi species theory proposed long time ago.
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