According To The New Sallybus of Sindh Text Book Board Jamshoro

2. Sajjad Hussain MiraniSajjad Hussain Mirani
Sindh University JamshoroSindh University Jamshoro
www.shm.usa.ccwww.shm.usa.cc

6. Introduction To VirusIntroduction To Virus
Virus is a Latin wordVirus is a Latin word venomevenome which means poison.which means poison.
Poisons which is carried through winds to various parts.Poisons which is carried through winds to various parts.
Virus was 1Virus was 1stst
reported in 1892 A.D. by a Russian biologistreported in 1892 A.D. by a Russian biologist
Iwanowsky,Iwanowsky, he stated that virus can spread from onehe stated that virus can spread from one
organism to another organism and from one person toorganism to another organism and from one person to
another person.another person.
There are many diseases which is considered to be caused byThere are many diseases which is considered to be caused by
filterable viruses.filterable viruses.
Virus was discovered by an American microbiologistVirus was discovered by an American microbiologist WendellWendell
StanleyStanley in 1935 A.D after invention of electronin 1935 A.D after invention of electron
microscope.

9. Viral CharacteristicsViral Characteristics
Viruses areViruses are non cellularnon cellular particles and all viruses areparticles and all viruses are
obligatory parasitesobligatory parasites..
Viruses lack necessary mechanism to replicate theirViruses lack necessary mechanism to replicate their
genetic material outside the host cell so they cant livegenetic material outside the host cell so they cant live
outside the host cell.outside the host cell.
Adhesion properties of virus depends upon their proteinAdhesion properties of virus depends upon their protein
biochemistry and envelop biochemistry.biochemistry and envelop biochemistry.
Size of Virus varies from 20 to 250 nm in size.Size of Virus varies from 20 to 250 nm in size.

12. Virulent And Temperate VirusesVirulent And Temperate Viruses
Viruses which destroy host cell after beingViruses which destroy host cell after being
replicated in host cells, are known asreplicated in host cells, are known as
virulent virusesvirulent viruses..
Viruses which do no destroy host cell andViruses which do no destroy host cell and
live in harmony with their host fromlive in harmony with their host from
generation to generation then it is knowngeneration to generation then it is known
asas temperate virustemperate virus..

15. Structure Of VirusStructure Of Virus
1.1. Viral ShapesViral Shapes
Viruses are of many shapes e.g. of little sphere shaped, golf ball like, tadpoleViruses are of many shapes e.g. of little sphere shaped, golf ball like, tadpole
like, rod shaped or polyhedral in shape.like, rod shaped or polyhedral in shape.
Usually viruses are helicular (rod / thread shape) or isometric (roughlyUsually viruses are helicular (rod / thread shape) or isometric (roughly
sphericle).sphericle).
2.2. Viral Genetic MaterialViral Genetic Material
Simple viruses contain single molecule ofSimple viruses contain single molecule of nucleic acidnucleic acid either DNA or RNAeither DNA or RNA
while complex viruses contain several molecules of nucleic acids.while complex viruses contain several molecules of nucleic acids.
3.3. Viral CapsidViral Capsid
It is a protein coat which encloses the viral genetic material.It is a protein coat which encloses the viral genetic material.
Capsid is made up of monomers calledCapsid is made up of monomers called capsomerscapsomers..
Number of capsomers is a characteristic feature of different viruses.Number of capsomers is a characteristic feature of different viruses.

20. 4.4. Viral EnvelopViral Envelop
In some viruses Capsid is enclosed by another layer ofIn some viruses Capsid is enclosed by another layer of
protein called envelop.protein called envelop.
Envelops usually increases the infectivity of virus.Envelops usually increases the infectivity of virus.
Also contain lipid in their structure.Also contain lipid in their structure.
5.5. Tail FibersTail Fibers
Few viruses like bacteriophage viruses contain tail plateFew viruses like bacteriophage viruses contain tail plate
with tail fibers.with tail fibers.
Tail fibers help virus to attach on the surface of theirTail fibers help virus to attach on the surface of their
host.host.

23. Classification Of VirusClassification Of Virus
Viruses are usually classified on the basisViruses are usually classified on the basis
of following features.of following features.
1.1. On The Basis Of Their Genetic MaterialOn The Basis Of Their Genetic Material
Viruses can be classified on the basis of theirViruses can be classified on the basis of their
genetic material into following classes,genetic material into following classes,
DNA virusDNA virus Have DNA as their genetic material.Have DNA as their genetic material.
RNA virusRNA virus Have RNA as their genetic material.Have RNA as their genetic material.

24. On The Basis Of Their MorphologyOn The Basis Of Their Morphology
On the basis of their morphology viruses mayOn the basis of their morphology viruses may
be of following typesbe of following types
Rod SHAPED e.gRod SHAPED e.g. tobacco mosaic virus.. tobacco mosaic virus.
SphericalSpherical e.g. polio virus.e.g. polio virus.
Tadpole SHAPED e.gTadpole SHAPED e.g. bacteriophage virus.. bacteriophage virus.

25. On The Basis Of Diversity
Name of group Nucleic Acid Example Infect
1. Un enveloped plus
strand RNA virus. RNA Polio and Rhino viruses Plant, bacteria and man
2. Enveloped plus strand
RNA virus. RNA
Hepatitis A and C
viruses
Arthropods and
vertebrates
3. Minus strand RNA
virus. RNA Rhabdo and Pox viruses Plants and animals
4. Retroviruses
RNA
HIV and Hepatitis B
viruses
Animals
5. Double strand RNA
virus. RNA Reo Viruses Plants and animals
6. Small genome DNA
virus. DNA Parvo viruses Animals
7. Medium and large
genome DNA virus.
DNA Herpes Viruses Man
8. Bacteriophage DNA Bacteria

28. Life Cycles Of Bacteriophage VirusLife Cycles Of Bacteriophage Virus
These are the various methods by whichThese are the various methods by which
bacteriophage virus replicates itself to formbacteriophage virus replicates itself to form
new viruses of its own kind.new viruses of its own kind.
Life cycle of Bacteriophage is of two typesLife cycle of Bacteriophage is of two types

29. Lytic CycleLytic Cycle
A type of life cycle which ends in to theA type of life cycle which ends in to the
death of host cell.death of host cell.
This type of association b/w virus andThis type of association b/w virus and
bacteria is known asbacteria is known as master – slavemaster – slave
relationshiprelationship as virus becomes masteras virus becomes master
and bacterial cell becomes slave.and bacterial cell becomes slave.
Viruses which only reproduce by lyticViruses which only reproduce by lytic
cycle are known as virulent viruses.cycle are known as virulent viruses.

30. What Happened in Lytic Cycle ?What Happened in Lytic Cycle ?
Phage virus stick on the surface of bacterial cell.Phage virus stick on the surface of bacterial cell.
Bacteriophage then insert its DNA in to the bacterial cell byBacteriophage then insert its DNA in to the bacterial cell by
contracting its tail and forming and hollow core through cellcontracting its tail and forming and hollow core through cell
wall and cell membrane of bacterial cell.wall and cell membrane of bacterial cell.
Viral DNA destroys DNA of bacterial cell and controls allViral DNA destroys DNA of bacterial cell and controls all
activities of bacterial cell.activities of bacterial cell.
Viral DNA use metabolic machinery of bacterial cell to formViral DNA use metabolic machinery of bacterial cell to form
various components of virus like Capsid and nucleic acids, etc.various components of virus like Capsid and nucleic acids, etc.
In the last viral DNA start forming enzymes which digestIn the last viral DNA start forming enzymes which digest
bacterial cell and newly formed viruses released and attacks onbacterial cell and newly formed viruses released and attacks on
new bacterial cells.new bacterial cells.

32. Lysogenic CycleLysogenic Cycle
In this cycle, viral DNA replicates inside theIn this cycle, viral DNA replicates inside the
bacterial cell without destroying bacterial cell.bacterial cell without destroying bacterial cell.
This type of association is known asThis type of association is known as host -host -
guest relationshipguest relationship b/w virus and bacteria.b/w virus and bacteria.
Viruses that replicate by using Lysogenic cycleViruses that replicate by using Lysogenic cycle
are known as temperate virusesare known as temperate viruses

33. What Happened In Lysogenic CycleWhat Happened In Lysogenic Cycle
Bacteriophage virus attached on the surface of bacterial cell.Bacteriophage virus attached on the surface of bacterial cell.
bacteriophage virus insert its DNA in bacterial cell.bacteriophage virus insert its DNA in bacterial cell.
viral DNA in bacterial cell incorporated in bacterial DNA insteadviral DNA in bacterial cell incorporated in bacterial DNA instead
of destroying bacterial DNA.of destroying bacterial DNA.
with each successive replication of bacterial DNA, viral DNAwith each successive replication of bacterial DNA, viral DNA
which is incorporated in bacterial DNA also replicated and thiswhich is incorporated in bacterial DNA also replicated and this
cycle is going on and on.cycle is going on and on.
Some times due to some environmental trigger, viral DNA exitsSome times due to some environmental trigger, viral DNA exits
bacterial DNA and initiate lytic cycle and causing death ofbacterial DNA and initiate lytic cycle and causing death of
bacterial cell.bacterial cell.

36. Transmission Of Viral DiseasesTransmission Of Viral Diseases
There are several routes by which viral diseases can beThere are several routes by which viral diseases can be
transferred from person to person, few important are astransferred from person to person, few important are as
follows.follows.
1.1.Droplet infections e.g. flu.Droplet infections e.g. flu.
2.2.Via infectedVia infected salivasaliva e.g. AIDS.e.g. AIDS.
3.3.Via infected feces e.g. hepatitis A and E.Via infected feces e.g. hepatitis A and E.
4.4.Via sexual intercourse e.g. AIDS and hepatitis B & C.Via sexual intercourse e.g. AIDS and hepatitis B & C.
5.5.Via wounds in skin e.g. Rabies and AIDS.Via wounds in skin e.g. Rabies and AIDS.

37. Viral Diseases In AnimalsViral Diseases In Animals
PoliomyelitisPoliomyelitis
Caused byCaused by polio viruspolio virus..
Disease of motor neurons present in anterior horn cells of spinalDisease of motor neurons present in anterior horn cells of spinal
cord.cord.
Largely under control by the development ofLargely under control by the development of polio vaccinepolio vaccine..
ColdsColds
Upper respiratory tract infection.Upper respiratory tract infection.
Caused byCaused by cold virusescold viruses, members of rhinovirus family., members of rhinovirus family.
Caused by many types of viruses so development of vaccine is veryCaused by many types of viruses so development of vaccine is very
difficult.difficult.

40. 3.3. EncephalitisEncephalitis
It isIt is inflammation of braininflammation of brain caused by virus.caused by virus.
Usually caused byUsually caused by arbovirusesarboviruses..
Very serious condition if not treated promptly.Very serious condition if not treated promptly.
4.4. DengueDengue
Also known as hemorrhagic fever.Also known as hemorrhagic fever.
Characterized by development of high grade fever.Characterized by development of high grade fever.
Caused byCaused by arbovirusesarboviruses, transmitted by a mosquito, transmitted by a mosquito
called aiedes eygepticus.called aiedes eygepticus.
5.5. Yellow FeverYellow Fever
Viral diseases caused byViral diseases caused by arbovirusesarboviruses..

46. 6.6. RabiesRabies
Also known asAlso known as hydrophobiahydrophobia..
Caused byCaused by rhabdovirusrhabdovirus..
These viruses are transmitted by the bite of animalsThese viruses are transmitted by the bite of animals
e.g. dog, wolves, bats, etc.e.g. dog, wolves, bats, etc.
Prompt treatment by the rabies vaccine is essentialPrompt treatment by the rabies vaccine is essential
other wise patient dies.other wise patient dies.
7.7. MeaslesMeasles
Caused byCaused by paramyxovirusesparamyxoviruses
8.8. MumpsMumps
Caused by paramyxoviruses.Caused by paramyxoviruses.
It is inflammation of parotid glands.It is inflammation of parotid glands.
A self limiting disease.A self limiting disease.

53. 9.9. FluFlu
Caused by flu viruses.Caused by flu viruses.
Spread as a droplet infection.Spread as a droplet infection.
Occur in world in epidemic formsOccur in world in epidemic forms

54. Viral Diseases In PlantsViral Diseases In Plants
In plants viral diseases are transmitted eitherIn plants viral diseases are transmitted either
by vertical or horizontal transmission.by vertical or horizontal transmission.
If plant get viral infection from their parentsIf plant get viral infection from their parents
then it is known as vertical transmission.then it is known as vertical transmission.
If plant aquired viral infection from someIf plant aquired viral infection from some
external source then it is known as horizontalexternal source then it is known as horizontal
transmission.transmission.

55. Different Viral Plant DiseasesDifferent Viral Plant Diseases
Viral diseases of plants can stunt their growth andViral diseases of plants can stunt their growth and
can even get capability to destroy whole crop.can even get capability to destroy whole crop.
Tobacco mosaic disease is a well known viralTobacco mosaic disease is a well known viral
infection of plants.infection of plants.
Agriculturists are unable to find cure of mostAgriculturists are unable to find cure of most
plant disease and they are trying to develop cropsplant disease and they are trying to develop crops
which are genetically resistant to viral infections.which are genetically resistant to viral infections.

58. Acquired Immune Deficiency SyndromeAcquired Immune Deficiency Syndrome
Commonly known asCommonly known as AIDSAIDS..
Causative agent is a virus known asCausative agent is a virus known as HIVHIV (human immune(human immune
deficiency virus), which is a member of retrovirus group.deficiency virus), which is a member of retrovirus group.
HIV binds to specific sites onHIV binds to specific sites on T4 lymphocytesT4 lymphocytes and made themand made them
unable to help or induce other white blood cells (e.g. killer cells,unable to help or induce other white blood cells (e.g. killer cells,
etc) to work against various microorganisms.etc) to work against various microorganisms.
Opportunistic infectionsOpportunistic infections are the cause of death in AIDS patients.are the cause of death in AIDS patients.
HIV carriers are those who are infected with HIV but do notHIV carriers are those who are infected with HIV but do not
develop AIDS.develop AIDS.

59. How HIV Transmits ?How HIV Transmits ?
Virus can be transmitted byVirus can be transmitted by sexual contact.sexual contact.
AIDS can be transmitted by theAIDS can be transmitted by the transfusion oftransfusion of
infected bloodinfected blood of patients having HIV.of patients having HIV.
HIV can be transmitted in intra venous drug abusersHIV can be transmitted in intra venous drug abusers
through infected needles.through infected needles.
Close association b/w infected and non infectedClose association b/w infected and non infected
peoplepeople (by cuts e.g. surgery on AIDS patient).(by cuts e.g. surgery on AIDS patient).
InfectedInfected womanwoman can pass disease tocan pass disease to her newbornher newborn
babybaby during pregnancy as well as during the period ofduring pregnancy as well as during the period of
breast feeding.breast feeding.

62. Signs And Symptoms Of AIDSSigns And Symptoms Of AIDS
Flu like illnessFlu like illness for a short while after infection is thefor a short while after infection is the
11stst
manifestation of AIDS.manifestation of AIDS.
After flu like illness patient can usually be symptom lessAfter flu like illness patient can usually be symptom less
for months and years.for months and years.
Due to deficiency of immune system, opportunisticDue to deficiency of immune system, opportunistic
infections start to produces their effects and patientinfections start to produces their effects and patient
develops pneumonia and other infections.develops pneumonia and other infections.
Other features of AIDS are weight loss, dementia (loss ofOther features of AIDS are weight loss, dementia (loss of
memory), and diarrhea.memory), and diarrhea.

64. Treatment Of AIDSTreatment Of AIDS
Scientist is working on two fields to treat AIDS i.e.Scientist is working on two fields to treat AIDS i.e.
to control disease and to develop a vaccineto control disease and to develop a vaccine
against AIDS.against AIDS.
The best available drugs against AIDS areThe best available drugs against AIDS are
azidothymidineazidothymidine (also known as zidovudine or(also known as zidovudine or
AZT).AZT).
AZT slow the progression of disease as well asAZT slow the progression of disease as well as
attack on virus present in brain (a major reservoirattack on virus present in brain (a major reservoir
of viruses.of viruses.

65. How To Prevent AIDS ?How To Prevent AIDS ?
There is no effective treatment againstThere is no effective treatment against
AIDS so disease can be prevented byAIDS so disease can be prevented by
acquiring safety measures.acquiring safety measures.

70. HepatitisHepatitis
Hepatitis meansHepatitis means inflammation of liver cellsinflammation of liver cells ..
Hepatitis can be caused by variety of agents likeHepatitis can be caused by variety of agents like virus,virus,
bacteria, drugs, toxinsbacteria, drugs, toxins, etc., etc.
Few sign and symptoms of hepatitis are jaundice,Few sign and symptoms of hepatitis are jaundice,
abdominal pain, liver enlargement, fatigue and some timeabdominal pain, liver enlargement, fatigue and some time
pyrexia.pyrexia.

71. Various Types Of HepatitisVarious Types Of Hepatitis
1.1. Hepatitis AHepatitis A
Virus transmitted byVirus transmitted by contaminated foodcontaminated food containcontain
virus.virus.
Contaminated waterContaminated water is major source of infection.is major source of infection.
Caused by non enveloped RNA virus.Caused by non enveloped RNA virus.

73. 2.2. Hepatitis BHepatitis B
There are estimatedThere are estimated 200 million carriers200 million carriers ofof
hepatitis B in world.hepatitis B in world.
Transmitted trough sexual contact, by infectedTransmitted trough sexual contact, by infected
blood, by intra venous drug abuse, etc and canblood, by intra venous drug abuse, etc and can
lead to liver cancer.lead to liver cancer.
VaccineVaccine is available which a best source ofis available which a best source of
prevention from hepatitis B.prevention from hepatitis B.
Caused by DNA virus.Caused by DNA virus.

76. 3.3. Hepatitis CHepatitis C
Caused by RNA virus and can be transmitted throughCaused by RNA virus and can be transmitted through
infected blood, sexual contact (rare), from mother to herinfected blood, sexual contact (rare), from mother to her
children, etc.children, etc.
Can alsoCan also lead to carrier stagelead to carrier stage..
CausedCaused cirrhosis of livercirrhosis of liver andand liver cancer,liver cancer, if notif not
treated promptly.treated promptly.
No vaccine is available.No vaccine is available.
Acute infections can be treated byAcute infections can be treated by interferoninterferon, which, which
can prevent development of carrier stage.can prevent development of carrier stage.

78. ViroidsViroids
Tiny naked, circular RNA molecules.Tiny naked, circular RNA molecules.
Infect plants only.Infect plants only.
RNA of viroids do not encode proteins in hostRNA of viroids do not encode proteins in host
cells.cells.
Viroids only replicate their RNA in host cells.Viroids only replicate their RNA in host cells.
Stunt growth of host plant cells.Stunt growth of host plant cells.

81. PrionsPrions
Self replicating infecting proteins molecules.Self replicating infecting proteins molecules.
Considered as mis folded protein molecules.Considered as mis folded protein molecules.
Mechanism of replication is not clear yet.Mechanism of replication is not clear yet.
Responsible for many degenerating brainResponsible for many degenerating brain
diseases.diseases.