The science of virusesvirology


 

Viruses and disease

Examples of common human diseases causedammonium sulfate or ethylene glycol, and
by viruses include the common cold, theremoval of cell components from a
flu, chickenpox and cold sores. Manyhomogenised cell mixture using organic
serious diseases such as Ebola, AIDS,solvents or enzymes to leave the virus
avian flu and SARS are also caused byparticles in solution.
viruses. The relative ability of virusesAssays to detect and quantify viruses
to cause disease is described in termsinclude:
of virulence. Other diseases are underHemagglutination assays, which
investigation as to whether they tooquantitatively measure how many virus
have a virus as the causative agent,particles are in a solution of red blood
such as the possible connection betweencells by the amount of agglutination the
Human Herpesvirus Six (HHV6) andviruses cause between them. This occurs
neurological diseases such as multipleas many viruses are able to bind to the
sclerosis and chronic fatigue syndrome.surface of one or more red blood cells.
Recently it was also shown that cervicalDirect counts using an electron
cancer is partially caused bymicroscope. A dilute mixture of virus
papillomavirus, representing evidence inparticles and beads of known size are
humans of a link existing between cancersprayed onto a special sheet and
and an infective agent. There is currentexamined under high magnification. The
controversy over whether the bornavirions are counted and the number
virus, previously thought of as causingextrapolated to estimate the number of
neurological disease in horses, could bevirions in the undiluted mixture.
responsible for psychiatric illness inPlaque assays involve growing a thin
humans.layer of host cells onto a culture dish
Viruses have many different mechanismsand adding a dilute mixture of virions
by which they produce disease in anonto it. The virions will infect and
organism, which largely depends on thekill the cells they land on, producing
species. Mechanisms at the cellularholes in the cell layer known as
level primarily include cell lysis, theplaques. The number of plaques can be
breaking open and subsequent death ofcounted and the number of virions
the cell. In multicellular organisms, ifestimated from it.
enough cells die the whole organism willDetection and subsequent isolation of
start to suffer the effects. Althoughnew viruses from patients is a
many viruses result in the disruption ofspecialised laboratory subject. Normally
healthy homeostasis, resulting init requires the use of large facilities,
disease, they may also exist relativelyexpensive equipment, and trained
harmlessly within an organism. Anspecialists such as technicians,
example would include the ability of themolecular biologists, and virologists.
herpes simplex virus, which causeOften, this effort is undertaken by
coldsores, to remain in a dormant statestate and national governments and
within the human body.shared internationally through
Epidemicsorganizations like the World Health
A number of highly lethal viralOrganization.
pathogens are members of thePrevention and treatment
Filoviridae. Filoviruses areBecause viruses use the machinery of a
filament-like viruses that cause viralhost cell to reproduce and also reside
hemorrhagic fever, and include the Ebolawithin them, they are difficult to
and Marburg viruses. The Marburg viruseliminate without killing the host cell.
attracted widespread press attention inThe most effective medical approaches to
April 2005 for an outbreak in Angola.viral diseases so far are vaccinations
Beginning in October 2004 and continuingto provide resistance to infection, and
into 2005, the outbreak was the world'sdrugs which treat the symptoms of viral
worst epidemic of any kind of viralinfections. Patients often ask for, and
hemorrhagic fever.physicians often prescribe, antibiotics.
Native American populations wereThese are useless against viruses, and
devastated by contagious diseases,their misuse against viral infections is
particularly smallpox, brought to theone of the causes of antibiotic
Americas by European colonists. It isresistance in bacteria. However, in
unclear how many Native Americans werelife-threatening situations the prudent
killed by foreign diseases after thecourse of action is to begin a course of
arrival of Columbus in the Americas, butantibiotic treatment while waiting for
the numbers have been estimated to betest results to determine whether the
close to 70% of the indigenouspatient's symptoms are caused by a virus
population. The damage done by thisor a bacterial infection[citation
disease may have significantly aidedneeded].
European attempts to displace or conquerPotential uses in therapy
the native population.Virotherapy uses viruses as vectors to
Detection, purification and diagnosistreat various diseases, as they can
In the laboratory, several techniquesspecifically target cells and DNA. It
for growing and detecting viruses exist.shows promising use in the treatment of
Purification of viral particles can becancer and in gene therapy[citation
achieved using differentialneeded]. Russian doctors have used
centrifugation, isopycnicphages as an alternative to antibiotics
centrifugation, precipitation withfor some time



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