Introduction to virology

1. Virology
Lecture 1
Dr.Nashwa Hamed

2. Why We Study
Viruses ??
• Viruses are all around us, comprising an
enormous proportion of our environment, in both
number and total mass.
• All living things encounter billions of virus
particles.

3. Every day
For example:
• They enter our lungs in the 6 liters of air each of us
inhales every minute.
• They enter our digestive systems with the food we eat.
• They are transferred to our eyes, mouths, and other
points of entry from the surfaces we touch and the people
with whom we interact.

4. Our Bodies Are
Reservoirs For viruses
- That reside in our respiratory, gastrointestinal, and urogenital
tracts.
- That can infect us.
- That loaded on our intestinal tracts with plant as well as
hundreds of bacterial species that harbor their own
constellations of viruses.

5. Viruses Can Cause
Human Disease
- With such constant exposure, it is no amazing that the vast
majority of viruses that infect us have little or no impact on
our health or well-being due to the immune defense systems,
which fights microbial infection.
- When these defenses are compromised, even the most
common infection can be lethal.

6. Viruses Can Cause
Human Disease
- Despite such defenses, some of the most devastating human
diseases have been or still are caused by viruses; these
diseases include smallpox, yellow fever, poliomyelitis,
influenza, measles, and AIDS.
- Viral infections can lead to life-threatening diseases. that
impact virtually all organs, including the lungs, liver, central
nervous system, and intestines.

7. Viruses Can Cause
Human Disease
- Viruses are responsible for approximately 20% of the human
cancer burden.
- Viral infections of the respiratory and gastrointestinal tracts
kill millions of children in the developing world each year.

8. Viruses Infect All
Living Things
- Viruses also infect pets, food animals, plants, insects, bacteria,
fungi, algae and wildlife throughout.

9. Viruses Can Be
Beneficial ???
- Viral infections in the ocean kill 20 to 40% of marine
microbes daily, converting these living organisms into
particulate matter, and in so doing release essential nutrients
that supply phytoplankton at the bottom of the ocean’s food
chain, as well as carbon dioxide and other gases that affect the
climate of the earth.

10. Viruses Can Be
Beneficial ???
- Infect and kill infectious agents Ex; bacteria and fungi.
- Infection by one virus can have an ameliorating effect on the
pathogenesis of a second virus or even bacteria.

11. Viruses Are Unique
Tools To Study
Biology
Studies of viruses have opened the path for many
discoveries in biological science.

12. Viruses Are Unique
Tools To Study
Biology
- Because viruses are dependent on their hosts for propagation,
studies that focus on viral reprogramming of cellular
mechanisms have provided unique insights into cellular biology
and functioning of host defenses.
- Bacteriophages studies laid the foundations of modern
molecular biology

13. Viruses Are Unique
Tools To Study
Biology
- Studies of animal viruses established many fundamental
principles of cellular function, including the presence of
intervening sequences in eukaryotic genes.

14. Viruses Are Unique
Tools To Study
Biology
- With the development of recombinant DNA technology and
our increased understanding of some viral systems, it has
become possible to use viral genomes as vehicles for the
delivery of genes to cells and organisms for both scientific and
therapeutic purposes “treat human disease via “gene therapy,”
in which functional genes delivered by viral vectors
compensate for faulty genes in the host cells.

15. Basics which must be studied??
• Viral discovery.
• Virus structure.
• Virus reproduction
• Importance of viruses in biology and disease.

16. Discovery of Viruses
History

17. • Although viruses have been known as distinct
biological entities for little more than 100
years, evidence of viral infection can be
found among the earliest recordings of human
activity, and methods for combating viral
disease were practiced long before the first
virus was recognized.

18. • Some modern viruses were undoubtedly
associated with the earliest precursors of
mammals and coevolved with humans.
• Other viruses entered human populations only
recently.

19. • The last 10,000 years of history was a time of
radical change for humans and our viruses??
✓ animals were domesticated,
✓ the human population increased dramatically,
✓ large population centers appeared,
✓commerce drove worldwide travel and
interactions among unprecedented numbers of
people.

20. History & Discovery
Evidence of several viral diseases can be
found in ancient records.

21. An Egyptian stele, or
stone
tablet, from the 18th
dynasty (1580–1350
b.c.) depicting a man
with a withered leg
and the “drop foot”
syndrome
characteristic of polio.

22. A painting for Tulips
by Nicolas Robert
(1624–1685), Striping
patterns (color
breaking) in tulips
were described in
1576 in western
Europe and were
caused by a viral
infection.

23. History & Discovery
Use of Vaccines
(Measures to control a viral disease)

24. • Jenner 1796 vaccinated an eight year old boy with material
removed from a cowpox lesion, Six weeks later, the boy was
inoculated with pus from a smallpox victim. The disease did
not develop, and the boy was immune to smallpox
• Jenner replaced his experiment on 23 persons using material
from cows (Latin vaccca) and hence the term (vaccination).
• The same procedure was carried out in 1800 by Dr. Benjamin
on his son Daniel and his two servants. They were fully
protected against smallpox.

25. History & Discovery
Suggestion of presence of Viruses

26. • The existence of viruses was suggested by Pasteur
1881 in connection with his work on rabies.
• Pasteur was unable to demonstrate the presence of
any visible microorganisms from rabid animals and
suggested that the causative agent might exist below
the range of microscopic visibility, that is according
to present terminology ultramicroscopic

27. • The invention of filters which do not allow the
passage of ordinary bacteria led to the discovery that
the causative agent of certain diseases is filterable.

28. • The First to observe this was Dmitrii Ivanowski, a
Russian (1892) and Martinus Beijerinck a Dutchman
(1898). They found that the agent responsible for the
mosaic disease of tobacco leaves is filterable. The filtrate
from an emulsion of diseased leaves was found to be
entirely free of bacteria, and no form living thing could
be seen when it was examined with ordinary microscope.
Nevertheless, when some of this clear filtrate was placed
upon healthy tobacco leaves, these leaves soon sickened
and showed every sing of the typical mosaic disease.

29. • These and other experiments convinced Beijerinck
that the elusive pathogen was not a bacterium but
contagium vivum fluidum meaning contagious living
fluid. Beijerinck was also the first person to use latin
word virus, meaning poison in its current sense. So
Beijerinck is considered to be the father of virology.

30. • In the same year Loeffler and Frosch (1898) showed
that the causal agent of the foot and mouth disease of
cattle, sometimes seen in man, was also filtrable.
• Other plant and animal disease were soon found to
be caused by similar agents. The nature of these
ultrafiltrable viruses, as they were initially called,
remained obscure for more than many years

31. • In 1915 F.W. Twort an English bacteriologist
working with plates showing contaminant in cowpox
vaccine observed a curious degenerative cellular
change in a culture to a staphylococcus culture, the
cells of the latter were affected in the same way,
showing that whatever caused the change was
transmissible.

32. • In 1917 D'Herelle a Franch-canadian bacteriologist
recorded his observation of the same effect: lysis of a
growing culture of a dysentery bacillus to which had
been added the filtrate from the feces of patients
suffering from bacillary dysentery. He was able to
demonstrate a rapid and generalized lysis of the
bacteria which could be transmitted in a prolonged
series of was cultures by adding small amount of the
filtrate from each preceding lysed culture.

33. • The essential features of this reaction have become
generally known as the Twort D'Herelle
phenomenon. The name that was applied to this lytic
substance bacteriophage (bacterio- bacterium,
bacteria -eater). Bacteriophages are frequently used
in the abbreviated form of phage.

34. In 1922 F.O. Maccallum and E.H. Oppenheimer
described the first successful attempts to purify a
poxvirus. Then Stanley (1935) working in the United
States succeeded in purifying tobacco mosaic virus
(TMV) particles and showed that they contained
protein. For this achievement he was awarded a Nobel
Prize.

35. But Stanley overlooked the essential component of
TMV. This was first detected in 1937 by F.C.Bawden
and N.W.Pirie, working in Britain. They demonstrated
that TMV was composed of ribonucleoprotein. The
type and approximate location of the nucleic acids
found in several plant viruses were determined by
Markman between 1950 and 1953.

36. -In spite of the high performance and advances made
in the design and construction of the compound of the
light microscope, it was only possible to detect the
large poxviruses under favorable conditions close to
the limit of resolution. The direct visualization of
viruses had to await the development of the more
powerful electron microscopy which appeared in an
experimental form between 1932 and 1936.

37. It is interesting to note that bacteriophages were
among the first biological specimens to be
photographed in the electron microscope.
The rapid development of high resolution/ electron
microscopes coupled with specimen preparation
techniques provided a wealth of information about
virus structure and physical dimensions.

38. Within a few years of the early bacteriophage and plant
virus studies the search of viruses infecting man, animals,
plants and bacteria expanded in many laboratories and
research institutes throughout the world.
In addition to the importance of diseases associated with
viral infection, the use of viruses as an experimental
system in the field of molecular biology and the new
methods for the study of virus composition, assembly and
structure have made spectacular advances.