Getting Technical
Other shapes are possible, including non-standard shapes that
combine both helical and icosahedral forms.
Viruses exist only to reproduce, spreading to new cells and
new hosts in many ways including:
• touch
• exchanges of saliva arising from coughing and sneezing
• sexual contact
• contaminated food or water
• insects that carry them from one person to another
Viruses can live on surfaces for some time; usually about three or
four days, so if a person touches an object with the virus on their
hands, the next person can pick up that virus by touching the
same surface.
Some viruses only affect one type of being, say, birds. If a virus
that normally affects birds does happen to get into a human, it
may pick up some human DNA leading to production of a new
type of virus that might be more likely to affect humans in future.
Examples of diseases caused by viruses in humans include:
• smallpox
• the common cold and different types of flu
• measles, mumps, rubella, chicken pox, and shingles
• hepatitis
• herpes and cold sores
• polio
• rabies
• Ebola and Hanta fever
• HIV, the virus that causes AIDS
• Severe acute respiratory syndrome (SARS)
• Dengue fever, Zika, and Epstein-Barr
When the immune system of the body detects a virus, it responds
to enable cells to survive the attack. The immune system
produces special antibodies that can bind to viruses, making them
non-infectious. The body also sends T cells to destroy the virus.
Most viral infections trigger these types of protective responses
from the immune system, but some viruses such as HIV and
neurotropic viruses have ways of evading the immune system’s
defences. Neurotropic viruses infect nerve cells. They can
affect the structure of the central nervous system (CNS) with
delayed and progressive effects that can be severe and can cause
diseases such as polio, rabies, mumps, and measles. Bacterial
infections can be treated with antibiotics, but viral infections
require either vaccinations to prevent them in the first place or
antiviral drugs to treat them. However, sometimes, the only
possible treatment is to provide symptom relief.
Antiviral drugs have been developed largely in response to
the AIDS pandemic. These drugs do not destroy the virus, but
they inhibit the viral activity inside cells which slows down the
progress of the disease. Antivirals are also now available to treat
infection with the herpes simplex virus, hepatitis B, hepatitis C,
influenza, shingles, and chicken pox. However, wherever possible,
the most effective and least costly defence against viruses
harmful to humans is by vaccinations. Anti-virus vaccines have
succeeded in eliminating diseases, such as smallpox and contain
one or more of:
• a weakened form of a particular virus
• viral proteins called antigens which stimulate the body to
form antibodies that will fight off future infections from the
same virus
• live-attenuated viruses, for example immunisation against
poliomyelitis.
There are risks, however, that these attenuated viruses can cause
the original disease in people who have weak immune systems.
Vaccinations are now available against polio, measles,
mumps, rubella, and several other diseases. Widespread use of
these vaccines has reduced their prevalence dramatically, for
example two doses of the measles vaccine offers 97% protection
against this disease.
Some people, for religious and other reasons choose not to
vaccinate their children. In the US they have become known as
‘Antivaxxers’ who ‘help breathe new life into old diseases’.
This article has been an introduction to viruses which are
harmful to humans and other living forms. There are, of course,
also ‘friendly’ viruses, some of which are helpful such as those
which attack or control potentially harmful bacteria such as e-coli
in digestive systems. However, most people tend to regard viruses
as potentially harmful or even as dangerous entities as evidenced
in the wry quotation attributed to the British microbiologist and
Nobel laureate, Peter Medawar, describing a virus as ‘a piece of
nucleic acid surrounded by bad news’. RACA
www.hvacronline.co.za RACA Journal I August 2020 39