Sajjad Hussain MiraniSajjad Hussain MiraniSindh University JamshoroSindh University Jamshorowww.shm.usa.ccwww.shm.usa.cc

Introduction To Introduction To VirusVirusVirus is a Latin word Virus 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 biologist reported in 1892 A.D. by a Russian biologist Iwanowsky,Iwanowsky, he stated that virus can spread from one he stated that virus can spread from one organism to another organism and from one person to organism to another organism and from one person to another person.another person.

There are many diseases which is considered to be caused There are many diseases which is considered to be caused by filterable viruses.by filterable viruses.

Virus was discovered by an American microbiologist Virus was discovered by an American microbiologist Wendell StanleyWendell Stanley in 1935 A.D after invention of in 1935 A.D after invention of electron microscope.electron microscope.

Viral CharacteristicsViral CharacteristicsViruses are Viruses are non cellularnon cellular particles and all viruses are particles and all viruses are obligatory parasitesobligatory parasites..

Viruses lack necessary mechanism to replicate their Viruses lack necessary mechanism to replicate their genetic material outside the host cell so they cant live genetic material outside the host cell so they cant live outside the host cell.outside the host cell.

Adhesion properties of virus depends upon their protein Adhesion 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.

Virulent And Temperate Virulent And Temperate VirusesViruses

Viruses which destroy host cell after being Viruses which destroy host cell after being replicated in host cells, are known as replicated in host cells, are known as virulent virusesvirulent viruses..

Viruses which do no destroy host cell and Viruses which do no destroy host cell and live in harmony with their host from live in harmony with their host from generation to generation then it is known generation to generation then it is known as as temperate virustemperate virus..

Structure Of VirusStructure Of Virus1. 1. Viral ShapesViral Shapes

Viruses are of many shapes e.g. of little sphere shaped, golf ball Viruses are of many shapes e.g. of little sphere shaped, golf ball like, tadpole like, rod shaped or polyhedral in shape.like, tadpole like, rod shaped or polyhedral in shape.

Usually viruses are helicular (rod / thread shape) or isometric Usually viruses are helicular (rod / thread shape) or isometric (roughly sphericle).(roughly sphericle).

2. 2. Viral Genetic MaterialViral Genetic MaterialSimple viruses contain single molecule of Simple viruses contain single molecule of nucleic acidnucleic acid either DNA either DNA or RNA while complex viruses contain several molecules of nucleic or RNA while complex viruses contain several molecules of nucleic acids.acids.

3. 3. Viral CapsidViral CapsidIt 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 called Capsid is made up of monomers called capsomerscapsomers..Number of capsomers is a characteristic feature of different Number of capsomers is a characteristic feature of different viruses.viruses.

4. 4. Viral EnvelopViral EnvelopIn some viruses Capsid is enclosed by another layer In some viruses Capsid is enclosed by another layer of protein called envelop.of 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 FibersFew viruses like bacteriophage viruses contain tail Few viruses like bacteriophage viruses contain tail plate with tail fibers.plate with tail fibers.Tail fibers help virus to attach on the surface of their Tail fibers help virus to attach on the surface of their host.host.

Classification Of VirusClassification Of VirusViruses are usually classified on the basis Viruses are usually classified on the basis of following features.of following features.

1. 1. On The Basis Of Their Genetic On The Basis Of Their Genetic MaterialMaterial

Viruses can be classified on the basis of their Viruses 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.

On The Basis Of Their On The Basis Of Their MorphologyMorphology

On the basis of their morphology viruses may On 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.

Spherical Spherical e.g. polio virus. e.g. polio virus.

Tadpole SHAPED e.gTadpole SHAPED e.g. bacteriophage virus.. bacteriophage virus.

On The Basis Of DiversityName 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

Life Cycles Of Bacteriophage Life Cycles Of Bacteriophage VirusVirus

These are the various methods by which These are the various methods by which bacteriophage virus replicates itself to form bacteriophage virus replicates itself to form new viruses of its own kind.new viruses of its own kind.

Life cycle of Bacteriophage is of two types Life cycle of Bacteriophage is of two types

Lytic CycleLytic CycleA type of life cycle which ends in to the A type of life cycle which ends in to the death of host cell.death of host cell.

This type of association b/w virus and This type of association b/w virus and bacteria is known as bacteria is known as master – slave master – slave relationshiprelationship as virus becomes master as virus becomes master and bacterial cell becomes slave. and bacterial cell becomes slave.

Viruses which only reproduce by lytic Viruses which only reproduce by lytic cycle are known as virulent viruses.cycle are known as virulent viruses.

What Happened in Lytic What Happened in Lytic Cycle ?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 by Bacteriophage then insert its DNA in to the bacterial cell by contracting its tail and forming and hollow core through cell contracting 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 all Viral 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 form Viral DNA use metabolic machinery of bacterial cell to form various components of virus like Capsid and nucleic acids, various components of virus like Capsid and nucleic acids, etc.etc.

In the last viral DNA start forming enzymes which digest In the last viral DNA start forming enzymes which digest bacterial cell and newly formed viruses released and attacks bacterial cell and newly formed viruses released and attacks on new bacterial cells. on new bacterial cells.

Lysogenic CycleLysogenic CycleIn this cycle, viral DNA replicates inside the In 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 as This 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 Viruses that replicate by using Lysogenic cycle are known as temperate virusescycle are known as temperate viruses

What Happened In Lysogenic What Happened In Lysogenic CycleCycleBacteriophage virus attached on the surface of Bacteriophage virus attached on the surface of

bacterial cell.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 viral DNA in bacterial cell incorporated in bacterial DNA instead of destroying bacterial DNA.DNA instead of destroying bacterial DNA.

with each successive replication of bacterial DNA, with each successive replication of bacterial DNA, viral DNA which is incorporated in bacterial DNA also viral DNA which is incorporated in bacterial DNA also replicated and this cycle is going on and on.replicated and this cycle is going on and on.

Some times due to some environmental trigger, viral Some times due to some environmental trigger, viral DNA exits bacterial DNA and initiate lytic cycle and DNA exits bacterial DNA and initiate lytic cycle and causing death of bacterial cell.causing death of bacterial cell.

Transmission Of Viral DiseasesTransmission Of Viral DiseasesThere are several routes by which viral diseases can be There are several routes by which viral diseases can be transferred from person to person, few important are as transferred 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 saliva saliva 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.

Viral Diseases In AnimalsViral Diseases In AnimalsPoliomyelitisPoliomyelitis

Caused by Caused by polio viruspolio virus..Disease of motor neurons present in anterior horn cells of spinal Disease of motor neurons present in anterior horn cells of spinal cord.cord.Largely under control by the development of Largely under control by the development of polio vaccinepolio vaccine..

ColdsColdsUpper respiratory tract infection.Upper respiratory tract infection.Caused by Caused by cold virusescold viruses, members of rhinovirus family., members of rhinovirus family.Caused by many types of viruses so development of vaccine is Caused by many types of viruses so development of vaccine is very difficult.very difficult.

3.3. EncephalitisEncephalitisIt is It is inflammation of braininflammation of brain caused by virus. caused by virus.Usually caused by Usually caused by arbovirusesarboviruses..Very serious condition if not treated promptly.Very serious condition if not treated promptly.

4. 4. DengueDengueAlso known as hemorrhagic fever.Also known as hemorrhagic fever.Characterized by development of high grade fever.Characterized by development of high grade fever.Caused by Caused by arbovirusesarboviruses, transmitted by a mosquito , transmitted by a mosquito called aiedes eygepticus.called aiedes eygepticus.

5. 5. Yellow FeverYellow FeverViral diseases caused by Viral diseases caused by arbovirusesarboviruses..

6. 6. RabiesRabiesAlso known as Also known as hydrophobiahydrophobia..Caused by Caused by rhabdovirusrhabdovirus..These viruses are transmitted by the bite of animals These 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 essential Prompt treatment by the rabies vaccine is essential other wise patient dies.other wise patient dies.

7. 7. MeaslesMeaslesCaused by Caused by paramyxovirusesparamyxoviruses

8. 8. MumpsMumpsCaused 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.

9. 9. FluFluCaused by flu viruses.Caused by flu viruses.Spread as a droplet infection.Spread as a droplet infection.Occur in world in epidemic forms Occur in world in epidemic forms

Viral Diseases In Viral Diseases In PlantsPlantsIn plants viral diseases are transmitted either In plants viral diseases are transmitted either

by vertical or horizontal transmission.by vertical or horizontal transmission.

If plant get viral infection from their parents If 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 some If plant aquired viral infection from some external source then it is known as horizontal external source then it is known as horizontal transmission.transmission.

Different Viral Plant Different Viral Plant DiseasesDiseases

Viral diseases of plants can stunt their growth Viral diseases of plants can stunt their growth and can even get capability to destroy whole and can even get capability to destroy whole crop.crop.

Tobacco mosaic disease is a well known viral Tobacco mosaic disease is a well known viral infection of plants.infection of plants.

Agriculturists are unable to find cure of most Agriculturists are unable to find cure of most plant disease and they are trying to develop plant disease and they are trying to develop crops which are genetically resistant to viral crops which are genetically resistant to viral infections.infections.

Acquired Immune Deficiency SyndromeAcquired Immune Deficiency SyndromeCommonly known as Commonly known as AIDSAIDS..

Causative agent is a virus known as Causative 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 on HIV binds to specific sites on T4 lymphocytesT4 lymphocytes and made them and 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 are the cause of death in AIDS patients.patients.

HIV carriers are those who are infected with HIV but do not HIV carriers are those who are infected with HIV but do not develop AIDS.develop AIDS.

How HIV Transmits ?How HIV Transmits ?Virus can be transmitted by Virus can be transmitted by sexual contact.sexual contact.

AIDS can be transmitted by the AIDS can be transmitted by the transfusion of transfusion of infected bloodinfected blood of patients having HIV. of patients having HIV.

HIV can be transmitted in intra venous drug abusers HIV can be transmitted in intra venous drug abusers through infected needles.through infected needles.

Close association b/w infected and non Close association b/w infected and non infected peopleinfected people (by cuts e.g. surgery on AIDS (by cuts e.g. surgery on AIDS patient).patient).

Infected Infected womanwoman can pass disease to can pass disease to her newborn her newborn babybaby during pregnancy as well as during the period during pregnancy as well as during the period of breast feeding. of breast feeding.

Signs And Symptoms Of AIDSSigns And Symptoms Of AIDSFlu like illnessFlu like illness for a short while after infection for a short while after infection is the 1is the 1stst manifestation of AIDS. manifestation of AIDS.

After flu like illness patient can usually be After flu like illness patient can usually be symptom less for months and years.symptom less for months and years.

Due to deficiency of immune system, Due to deficiency of immune system, opportunistic infections start to produces their opportunistic infections start to produces their effects and patient develops pneumonia and effects and patient develops pneumonia and other infections.other infections.

Other features of AIDS are weight loss, dementia Other features of AIDS are weight loss, dementia (loss of memory), and diarrhea. (loss of memory), and diarrhea.

Treatment Of AIDSTreatment Of AIDSScientist is working on two fields to treat AIDS Scientist is working on two fields to treat AIDS i.e. to control disease and to develop a vaccine i.e. to control disease and to develop a vaccine against AIDS.against AIDS.

The best available drugs against AIDS are The 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 as AZT slow the progression of disease as well as attack on virus present in brain (a major attack on virus present in brain (a major reservoir of viruses.reservoir of viruses.

How To Prevent How To Prevent AIDS ?AIDS ?There is no effective treatment against There is no effective treatment against

AIDS so disease can be prevented by AIDS so disease can be prevented by acquiring safety measures.acquiring safety measures.

HepatitisHepatitisHepatitis means Hepatitis means inflammation of liver cellsinflammation of liver cells..

Hepatitis can be caused by variety of agents like Hepatitis can be caused by variety of agents like virus, bacteria, drugs, toxinsvirus, bacteria, drugs, toxins, etc., etc.

Few sign and symptoms of hepatitis are Few sign and symptoms of hepatitis are jaundice, abdominal pain, liver enlargement, jaundice, abdominal pain, liver enlargement, fatigue and some time pyrexia.fatigue and some time pyrexia.

Various Types Of HepatitisVarious Types Of Hepatitis1. 1. Hepatitis AHepatitis AVirus transmitted by Virus transmitted by contaminated foodcontaminated food contain virus.contain virus.

Contaminated waterContaminated water is major source of is major source of infection.infection.

Caused by non enveloped RNA virus.Caused by non enveloped RNA virus.

2. 2. Hepatitis BHepatitis BThere are estimated There are estimated 200 million carriers200 million carriers of of hepatitis B in world.hepatitis B in world.

Transmitted trough sexual contact, by infected Transmitted trough sexual contact, by infected blood, by intra venous drug abuse, etc and can blood, by intra venous drug abuse, etc and can lead to liver cancer.lead to liver cancer.

VaccineVaccine is available which a best source of is available which a best source of prevention from hepatitis B.prevention from hepatitis B.

Caused by DNA virus.Caused by DNA virus.

3. 3. Hepatitis CHepatitis CCaused by RNA virus and can be transmitted Caused by RNA virus and can be transmitted through infected blood, sexual contact (rare), through infected blood, sexual contact (rare), from mother to her children, etc.from mother to her children, etc.

Can also Can also lead to carrier stagelead to carrier stage..

Caused Caused cirrhosis of liver cirrhosis of liver andand liver cancer, liver cancer, if if not treated promptly.not treated promptly.

No vaccine is available.No vaccine is available.

Acute infections can be treated by Acute infections can be treated by interferoninterferon, , which can prevent development of carrier stage. which can prevent development of carrier stage.

ViroidsViroidsTiny naked, circular RNA molecules.Tiny naked, circular RNA molecules.

Infect plants only.Infect plants only.

RNA of viroids do not encode proteins in host RNA 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.

PrionsPrionsSelf replicating infecting proteins Self replicating infecting proteins

molecules.molecules.

Considered as mis folded protein Considered as mis folded protein molecules.molecules.

Mechanism of replication is not clear yet.Mechanism of replication is not clear yet.

Responsible for many degenerating brain Responsible for many degenerating brain diseases.diseases.