Biology Reference
In-Depth Information
1. Where dId It All BegIn? A hIStory oF VnPs: FroM
PAthogenS to BuIldIng BloCKS
The word
is Latin and means “poison.” Viruses are infectious agents,
and generally pathogens. It was not, however, until the end of the 19th
century that viruses were discovered as infectious agents. The first virus
to be recognized as an infectious agent distinct from bacteria was the plant
pathogen
virus
(TMV) (Zaitlin, 1898). Today more than
5,000 viruses have been discovered and described, although this likely
represents a fraction of those found in nature. Viruses cause many human
diseases, from the common cold and chicken pox to more serious infections
such as AIDS (acquired immune deficiency syndrome, which is caused by the
Human immunodeficiency virus
Tobacco mosaic virus
[HIV]) and SARS (severe acute respiratory
syndrome, which is caused by SARS coronavirus). Virology — the science of
studying viruses — is thus a highly important discipline in regard to human
health.
Viruses infect all forms of life. Generally, animal viruses infect animals,
including humans; plant viruses infect plants; and bacteriophages infect
bacteria. Archaeal viruses are those that infect Archaea. Archaea show
similarities with bacteria as well as with eukaryotes, and although they are
prokaryotes, it has been suggested that they are more closely related to the
eukaryotes (Woese & Fox, 1977).
In their simplest form, viral particles consist of a nucleic acid genome and
a protective protein coat termed the capsid. Some viruses have additional
structural features such as a lipid envelope, or they may consist of separate
head and tail structures (discussed in Chapter 2). In brief, the nucleic acid
genome encodes the genetic information that is needed to produce viral
progeny. In addition to cellular attachment, an important function of the
capsid of non-enveloped viruses is the protection of the nucleic acid genome.
This tends to make non-enveloped viral particles extremely robust. With a few
exceptions, nearly all viruses utilized in nanotechnology are non-enveloped
particles. The envelope for enveloped viruses also plays a role in the initial
stages of the infection process, including binding to surface receptors and
internalization into the host cell.
Viruses have now been studied for more than 100 years, and detailed
knowledge about the structure and function of many viruses has been
gathered. For many years the emphasis has been on the understanding of
viral infection and disease, and it still is. Being able to control or treat viral
infections is an important goal in human medicine (as well as veterinary
medicine and agriculture). Every year novel viruses or virus strains evolve
with the potential to cause disease and death worldwide. For instance, at the
time of writing this topic, the
Influenza
virus strain H1N1 (also referred to as
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