Virology 1st sem MSc

1. Virology
Sub topic :viral taxonomy

2. Virology
● Virology is the study of viruses and
virus like agents including there
taxonomy, diseases producing
properties, culture and genetics
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3. Viruses
● Viruses are simple, non-cellular, verry small sub-microscopic biological
entities consisting of one or more molecules of either DNA or RNA
genome enclosed in a coat of protein.
● Viruses can reproduce only within living cells and are obligate
intercellular parasites which lack cellular organization.
● They are small in size ranging from 0.02 um to 0.3um.
● Smallpox is largest virus about 200 nm in diameter and
Polio virus is smallest virus about 28 mm in diameter.
● Viruses vary in shape from the simple helical and
icosahedral to more complex structure.
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4. Brief outline on discovery of viruses
In 1884 CHAMBERLAND
development a porcelain filter
that allowed the passing of
fluid but not bacteria.
The filter was useful in
sterilization of liquids.
CHAMBERLAND PORCELAIN FILTER
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5. In 1886 A. MAYER demonstrated
that the sap of mosaic leaves of
tobacco plant developed the
mosaic symptom when injected
into the healthy plants.
The infectivity of the sap was
destroyed by boiling and then He
thought that the causal agent was
bacteria and he inoculated a
healthy leave with large number of
bacteria but it failed to develop
mosaic symptom.
Tobacco plant
showing mosaic
pattern on leaf
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6. In 1892 DMITRI IWANOWSKI an Russian
botanist for the first time filtered the sap
of diseased tobacco plant through the
porcelain filter to obtain bacteria , but the
infectious agent was filtered through the
pores of porcelain filter.
After injecting of filtered sap he found the
development of mosaic symptom.
So he concluded that the infectious agent
as Poisonous fluid.
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7. In 1898 a Dutch microbiologist
M.V BEIJERINK put a concept
(contagium vivum fluidum) living
infectious fluid.
He observed that the behaviour of
filterable cell (virus) was different
from the bacteria and he coined
the Latin name “Virus” meaning
poison.
M.V BEIJERINK
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8. In 1935 WEDELL STANLEY an
American chemist . He Crystallized
Sap from diseased tobacco plant and
he found that the crystals when
inoculated on a healthy tobacco plant
it courses infection .
He included that the viruses were not
like a typical cell of the living
organisms and he received Nobel
prize in 1964.
WEDELL STANELY
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9. The two British biochemists
F.C. BAWDEN and N.W.PIRIE
in 1938 analyzed the
Crystallized particles and
demonstrated that they were
made up of Protein and
Ribonucleic acid (RNA) and
they received Nobel prize.
F.C.BAWDEN
N.W.PIRIE
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10. In 1956 GIRRER and
SCHRAMM proved that the real
nature of nucleic acid as
infectious agent and Genetic
material.
GIRREN SCHRAMM
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11. In 1956 FRAENKEL CONRAT
confirmed that the Genetic
material of tobacco mosaic
virus (TMV) is the RNA.
FRAENKEL CONRAT
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12. In the early 20th century the
English bacteriologist
FREDERICK TWORT
discovered viruses that
infect bacteria
Example: bacteriophage
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13. In 1931 with the invention of the
Electronic microscope by
German engineer's ERNST
RUSKA and MAXKNOLL came
with the First image of viruses.
ERNST RUSKA MAXKNOLL
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14. FIRST ELECTRON MICROSCOPE. 14

15. Nomenclature of viruses
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16. Nomenclature of viruses is a system for giving names or
naming of viruses
First Binomial system of nomenclature was used, which has
two names one was genus and another was species, but they
did not support virus naming.
Then come International Committee for Virus Nomenclauture
(ICTVN) in 1968. it has two name:-
First name is – COMMON NAME
Second name is – CODED INFORMATION (cryotogram)
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17. ICVN
CODED INFORMATION COMMON NAME
THIRD PAIR
FIRST PAIR
SECOND PAIR
FOURTH PAIR
[TYPES OF NUCLEIC ACID / NUMBER OF HELIX]
[MOLICULAR WEIGHT OF NUCLEIC ACID /
PERCENTAGE OF NUCLEIC ACID]
[VIRUS SIZE / SIZE OF NUCLEIC PROTEIN]
[HERPETIC VARIETY / CARRIER USED
IN TRANSMISSION]
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18. CLASSIFICATION OF VIRUSES
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19. In 1927, JOHANSON was the first person to attempt for the
classification of plant viruses.
Traditionally viruses have been named according to the diseases
caused by them by adding a suffix virus.
Example: Poliovirus , Influenza virus ,etc.
In Bacteriophages they are named after the laboratory codes.
Example: QB, M13, etc.
The Cyanophages were named after the host they lysed and the
serological differences among them.
Example: LPP1 and LPP2.
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20. In 1948 HOLMES followed the Linnean system of binomial nomenclature and put
the viruses into an order Virales and 3 suborders.
1)PHAGINAE – viruses attacking on bacteria.
2)PHYTOPHAGINAE - viruses attacking on plant.
3)ZOOPHAGINAE - viruses attacking on animal.
VIRALES
PHAGINAE PHYTOPHAGINAE ZOOPHAGINAE
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21. LHT System of classification.
In 1962 , A. Lwoff , R. Horne and P.Tournier proposed a system of classification
of viruses which is commonly refereed to as LHT system of classification.
They are grouped into one phylum (vira) with two subphyla based on RNA
(Ribovira) and DNA (Deoxyvira) present in virions.
VIRA
DEOXYVIRA
(DNA Virus)
RIBOVIRA
(RNA Virus)
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22. 22

23. 23

24. BELLET in 1967 proposed a system of classification. This system of
classification is based mainly on two criteria of viral particles namely
1) Molecular weight.
2) Percentage of guanine + cytosine of nucleic acid.
GIBBS in 1969 proposed a system of classification for plant viruses which is
known as Gibbs system of classification. The criteria to classify the viruses are
1) SHAPE OF CAPSID.
2) MODE OF TRANSMISSION.
3)TYPE OF VECTOR.
4)SYMPTOMS ON HOST AFTER INFECTION.
5)THE NATURE OF ACCESSORY PARTICLES.
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25. CASJENS AND KINGS CLASSICATION OF VIRUS
In 1975 CASJENS and KINGS classified virus into 4 groups
based on type of nucleic acid, presence or absence of an
envelope and site of assembly and also on symmetry.
It Is as follows:
1) SINGLE STRANDED RNA VIRUSES
2) DOUBLE STRANDED RNA VIRUSES
3) SINGLE STRANDED DNA VIRUSES
4) DOUBLE STRANDED DNA VIRUSES
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26. 26

27. 27

28. BALTIMORE CLASSIFICATION OF VIRUSES.
In 1971 DAVID BALTIMORE classified viruses into one of 7 groups depending on
a combination of their nucleic acid (RNA or DNA) on their manner of messenger
RNA synthesis , standness ( single or double stranded ), sense (+ or -) and
method of replication , groups are designated by Roman numerals
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29. Baltimore grouped / classified viruses into 7 groups namely :
GROUP 1 :- ds DNA Viruses
Example :- Adenoviruses, Herpesviruses, Poxviruses.
GROUP 2 :- ss DNA Viruses [+strand or sense ] DNA
Example :-Parvoviruses.
GROUP 3 :- ds RNA Viruses
Example :- Reoviruses
GROUP 4 :- ss RNA Viruses [+ strand or sense ] RNA
Example :- Picornaviruses , Togaviruses.
GROUP 5 :- (-) ss RNA Viruses (- strand or antisense) RNA
Example:- Orthomyxoviruses , Rhabdoviruses.
GROUP 6 :- ss RNA–RT Viruses (+strand or sense ) RNA with DNA intermediate in life cycle
Example :-Retroviruses.
GROUP 7 :- ds DNA-RT Viruses.
Example :- Hepadnaviruses.
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30. 30

31. INTERNATIONAL COMMITTEE ON TAXONOMY OF
VIRUSES [ICTV].
The ICTV began to devise and implement rules for the naming and
classification of viruses in 1966.
The ICTV has a task of developing, refining and maintaining a universal
viruses taxonomy.
The name and order of families are italicized.
The main criteria of ICTV is to identify each species, then listed species
according to the criteria.
For some viruses their taxonomic status cannot be determined so such
viruses are listed as Tentative species.
Viral classification starts at the level of order and
continues as follows, with the taxon suffixes.
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32. VIRUS CLASSIFICATION
ORDER – VIRALES.
FAMILY – VIRIDAE.
SUB-FAMILY - VIRINAE.
GENUS – VIRUS.
SPECIES – generally takes the form of (disease) virus.
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33. In 2012 , 7 orders, 96 families, 22 sub-families, 420 genera and 2,618 species
of viruses have been defined by the ICTV.
The 7 orders are
Caudovirales :- they are tailed dsDNA , Bacteriophages.
Herpesvirales:- contain large eukaryotic dsDNA viruses.
Ligmenvirales:- contain linear, dsDNA viruses.
Mononegavirales:- it include non-segmented (-) strand ssRNA plant and animal
viruses.
Nidovirales:- they are composed of (+) strand ssRNA viruses with vertebrate as
host
Picornavirales :- it contains small (+) strand ssRNA viruses that infects a variety
of plant, insect and animal hosts.
Tymovirales:- they contain monopartite (+) ssRNA viruse4s that infect plants.
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34. In 2019 they have been ranked into 15 ranks from Realm to Species.
REALM – VIRIA .
SUBREAL – VIRA.
KINGDOM – VIRITES.
SUBKINGDOM – VIRITES .
PHYLUM – VIRICOTA .
SUBPHYLUM – VIRICOTINA .
CLASS – VIRICETES.
SUBCLASS – VIRICETIDAE .
ORDER – VIRALES .
SUBORDER – VIRINEAE .
FAMILY – VIRIDAE.
SUBFAMILY – VIRINAE .
GENUS – VIRUS .
SUBGENUS – VIRUS .
SPECIES - …………
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35. 35

36. INFLUENZA
VIRUS.

37. Influenza is a animal viral disease, commonly referred to as the Flu.
Flue is an infectious viral disease caused by RNA viruses of the family
Ortho-myxoviridae [influenza virus] that affects birds and mammals.
It has 2 antigens H and N
H - ANTIGEN - It initiates infection and attachment of viruses to
susceptible cell.
N - ANTIGEN – It is responsible for the release of the virus from the
infected cell.
Influenza are divided into 3 types :
Influenza A
Influenza B
Influenza C
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38. INFLUENZA A.
Influenza A virus is further classified into subtype according to the combinations
of the Hemagglutinin (HA) and the Neuraminidase (NA), are the proteins on the
surface of the virus.
This type of virus is the most virulent human pathogen among the three types and
cause the most severe disease.
It affects both animal and birds
H1N1 which caused Spanish flue in 1918 and 2009 flu pandemic.
H2N2 which caused Asian flu in 1957.
H3N2 which caused Hong Kong flu in 1968.
H5N1 it also caused pandemic threat in 2018.
H7N7 it has unusual zoonotic potential.
H1N2 caused endemic in human and pig.
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39. INFLUENZA B.
Influenza B viruses change only by the more gradual process of
antigenic drift, it almost exclusively infect humans and less common
than influenza A .
This type of influenza mutates at a rate 2 - 3 times lower than type A ,
this reduced the rate of antigenic change.
It is not a pandemic disease.
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40. INFLUENZA C.
Influenza C virus infection usually causes either a very
mild respiratory illness or no symptoms at all.
It infects humans , dogs ,pigs.
Sometime causes both severe illness and local
epidemics.
It is less common than the other type and usually causes
mild disease in children.
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41. STRUCTURE. Influenza virus A,B,C are very similar in
overall structure.
The virus particle is 80- 120 nm in
diameter and usually roughly spherical,
although filamentous forms can occur.
these filamentous forms are more
common in Influenza C.
It will form cord like structures upto 500
micrometers long on the surface of
infected cells.
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42. Hemagglutinin (HA) and Neuraminidase (NA) are the
two large glycolproteines on the outside of the viral
particles.
HA is Lectin that mediates binding of the target cell
and entry of the viral genome into the target cell.
NA is involved in the release of progeny virus from
infected cell by cleaving sugars that bind the mature
viral particles.
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43. CLINICAL MANIFESTATIONS (symptoms)
• FEVER
• COUGH
• SORE THROAT
• RUNNING OR
STUFFY NOSE
• HEADACHE
• MUSCLE ACHES
• EXTREME
FATIGUE
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44. MODE OF TRANSMISSION.
Influenza is spread mainly from person to person by
droplets infection or droplet nuclei created by
Sneezing
Coughing
Talking
The portal of entry of the virus is the respiratory tract.
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45. DIAGNOSIS.
● Virus isolation from Nasopharyngeal secretions are
the best specimens for obtaining large quantities of
viral infected cells.
● Paired sera A serodiagnosis of influenza A and B can
be made by the examination of two serum specimens
from a patient .
● Serology and rapid tests.
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46. PREVENTION.
● The Flu shot - an inactivated vaccine
(containing killed virus) that is given
as vaccine usually in the arm.
● The Nasal spray flu vaccine – a
vaccine made with live weakened flu
viruses that is given as a nasal spray
( live attenuated influenza vaccine
called LAIV)
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47. TREATMENT.
It includes a range of medications and therapied :-
● Antiviral drugs like Acetaminophen or Ibuprofen.
● Increasing liquid intake.
● Warm showers and warm compresses especially in
the nasal area, can reduce the body aches and nasal
congestions.
● Use of nasal strips and humidifiers help in reduce
congestions during sleep.
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48. Reference
1)viral taxonomy – Andrew M.Q. King , Michael .J et.al
2)A Textbook of Microbiology– R.C Dubey and D.K Maheshwari
3) Microbiology – R.P. Singh.
4) Molecular Virology .
5) Websites :- thebiologynotes.com
Wikipedia.
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49. THANK YOU.
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