Virus and Host Cells
If a virus does not come into contact with its host cell, can it die? If
so how long would it take for this to occur. For example if the HIV virus
did not come into contact with its host cell (a lymphocyte) would it die,
and if so how long would it take?
One of the treatments for HIV is to "plug" the receptor sites on the host
cell where they grab on, or to fool the HIV into plugging into a fake HIV
molecule. It is not probable that if these treatments were not given that
virus would not find a cell because the virus is in such high numbers.
Since a virus is technically not a living organism, it can't die. Scientists
have decided that to be considered a living organism, something must have 5
qualities: 1) be made of one or more cells, 2) have a metabolism (i.e.,
reactions that break down food molecules, make proteins, etc.), 3) grow and
develop, 4) reproduce, and 5) respond to stimuli. A virus particle is
basically a protein shell of some kind that houses a bit of nucleic acid
(either DNA or RNA, depending on the virus), and maybe a few enzymes that
will be active in the infected cell. Picture a miniature syringe and
hypodermic needle, filled with DNA, and you have a pretty good image of a
virus. So it's not living to begin with.
That being said, let's ask, does a virus ever lose the ability to infect
cells, which is really what your question was getting at. The answer is yes,
although the length of time this can take can vary greatly. All DNA and
protein is susceptible to damage from the environment; if not repaired, the
information encoded in the DNA can be lost, and proteins can lose their
ability to function. Your cells repair damaged DNA and replace many (but not
all) damaged or old proteins. A virus stored in a test tube for months or
years can't do this, so _eventually_ it will lose its ability to infect. The
time required for this depends largely on environmental conditions, e.g., it
will happen faster at room temperature than if stored in the refrigerator.
Viruses are strange particles that exist in the gray area between life and
non-life. Here's food for thought: While not living organisms, they DO
evolve, meaning they accumulate random mutations that either help or hinder
the next generation of viruses. Of course, to get the next generation, they
need to infect a cell and use its machinery to make more viruses.
Paul Mahoney, Ph.D.
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Update: June 2012