| Viruses and Other Non-living Infectious Agents |
Viruses and Other Non-living Infectious Agents
- A virus is an acellular agent that is
infectious, it is small and has one or many
pieces of nucleic acid. It can infect
humans, animals, plants and bacteria and
cause disease. Viruses have a much simpler
structure then a bacteria. They do not have
cell membranes and are made up of only a few
organic molecules. Viruses and viroids do
not carry out metabolism, such as transport
of nutrients across a cell membrane.
- The major viral characteristics: type of
genetic material (DNA or RNA, single or
double stranded), viral size, capsid
structure and target host are used to
determine how best to classify a virus.
- Viral genomes can be linear, one piece
or several molecules of nucleic acid
(similar to eukaryotic chromosomes).
- Not all viruses are as specific to a
host (although most are). Some can infect
many different hosts and different tissues
within a host. An example of a �generalist�
virus is rabies. Rabies can infect many
different mammals from humans to dogs to
bats.
- Viruses have three basic capsid shapes:
helical, polyhedral and complex.
- An envelope surrounds certain viruses.
Enveloped viruses acquire their envelope
from the host cell during viral replication
or when the viral is released from the cell.
- A virion without an envelope is called a
nonenveloped or naked virion.
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