Prepared by :-

Mohammed Osama El-Ifranji

Classification of Medically Important Viruses

Introduction Introduction

The classification of viruses is based on The classification of viruses is based on chemicalchemical and and morphologicmorphologic criteria criteria..

The two major components of the virus The two major components of the virus used in classification are used in classification are :- :-

1.1. The nucleic acid The nucleic acid ((its molecular weight its molecular weight and structureand structure))

2.2. the capsid the capsid ((its size and symmetry and its size and symmetry and whether it is envelopedwhether it is enveloped). ).

Classification of DNA VirusesClassification of DNA VirusesVirus Virus FamilyFamily

Envelope Envelope PresentPresent

Capsid Capsid SymmetrySymmetry

Particle Particle size size ((nm)nm)

DNA DNA MW MW ((x106)x106)

DNA DNA

StructureStructure Medically Medically Important Important VirusesViruses

ParvovirusParvovirusNoNoIcosahedralIcosahedral222222SS, linearSS, linearB19 virusB19 virus

PapovavirusPapovavirusNoNoIcosahedralIcosahedral55553–53–5DS, circular, DS, circular, supercoiledsupercoiled

PapillomavirusPapillomavirus

AdenovirusAdenovirusNoNoIcosahedralIcosahedral75752323DS, linearDS, linearAdenovirusAdenovirus

HepadnavirusHepadnavirusYesYesIcosahedralIcosahedral42421.51.5DS, DS, incomplete incomplete circularcircular

Hepatitis B Hepatitis B virusvirus

HerpesvirusHerpesvirusYesYesIcosahedralIcosahedral100 100 100–100–150150

DS, linearDS, linearHerpes simplex Herpes simplex virus, varicellavirus, varicella--zoster virus, zoster virus, cytomegalovirucytomegalovirus, Epsteins, Epstein--Barr Barr virusvirus

PoxvirusPoxvirusYesYesComplexComplex250 250 xx 400400

125–125–185185

DS, linearDS, linearSmallpox virus, Smallpox virus, vaccinia virusvaccinia virus

DNA Viruses DNA Viruses Parvoviruses Parvoviruses These are very small These are very small ((22 nm in diameter22 nm in diameter) ) naked icosahedra viruses with singlenaked icosahedra viruses with single--stranded stranded

linear DNAlinear DNA.. There are two types of parvoviruses There are two types of parvoviruses :-:-

1.1. The defective parvovirusesThe defective parvoviruses . . ee..gg.., adeno, adeno--associated virus associated virus require a helper virus for replication require a helper virus for replication The DNA of defective parvoviruses isThe DNA of defective parvoviruses is unusual unusual

because plusbecause plus--strand DNA and minusstrand DNA and minus--strand strand DNA are carried in separate particlesDNA are carried in separate particles. .

2. The nondefective parvoviruses2. The nondefective parvoviruses best illustrated by B19 virus which best illustrated by B19 virus which

associated with : - associated with : - aplastic crises in sickle cell anemia aplastic crises in sickle cell anemia

patients patients erythema infectiosum ?!! erythema infectiosum ?!!

childhood disease characterized by a childhood disease characterized by a "slapped-cheeks" rash, fever ,headach "slapped-cheeks" rash, fever ,headach and rash in (face,trunk,extremities ) and rash in (face,trunk,extremities )

Note / may confused with rubella.Note / may confused with rubella.

Papovaviruses Papovaviruses These are naked icosahedra viruses (55 nm in

diameter) doubledouble--stranded circular supercoiled DNA stranded circular supercoiled DNA ""papovapapova" " is an acronym of is an acronym of papapilloma, pilloma, popolyoma, lyoma,

and simian and simian vavacuolating viruses cuolating viruses Three human papovavirusesThree human papovaviruses : : 1.1. JC virus JC virus progressive multifocal progressive multifocal

leukoencephalopathy leukoencephalopathy 2.2. BK virus :BK virus : from the urine of from the urine of

immunosuppressed kidney transplant patients immunosuppressed kidney transplant patients 3.3. human papillomavirus . human papillomavirus . NoteNote/Polyomavirus (mice ), simian vacuolating /Polyomavirus (mice ), simian vacuolating

virus 40virus 40 (monkeys ) induce (monkeys ) induce malignant tumors malignant tumors

AdenovirusesAdenoviruses These are naked icosahedral viruses These are naked icosahedral viruses ((75 75

nm in diameternm in diameter) ) doubledouble--stranded linear DNAstranded linear DNA.. There are at least 40 antigenic typesThere are at least 40 antigenic types some of which cause sarcomas in animals some of which cause sarcomas in animals

but but nono tumors in humans tumors in humans..

Note/Note/ They cause pharyngitis, upper and They cause pharyngitis, upper and lower respiratory tract diseaselower respiratory tract disease

Hepadnaviruses Hepadnaviruses These are These are doubledouble--shelledshelled viruses viruses ((42 nm 42 nm

in diameterin diameter)) an icosahedral capsid covered by an an icosahedral capsid covered by an

envelope envelope The DNA is a doubleThe DNA is a double--stranded circle that stranded circle that

is unusual is unusual ؟؟؟؟

because the complete strand is not a because the complete strand is not a covalently closed circle and the other covalently closed circle and the other strand is missing approximately 25% of strand is missing approximately 25% of its length .its length .

e.g./Hepatitis B virus (human)e.g./Hepatitis B virus (human)

Herpesviruses Herpesviruses These are enveloped viruses These are enveloped viruses ((100 nm in 100 nm in

diameterdiameter)) icosahedra nucleocapsid and doubleicosahedra nucleocapsid and double--stranded stranded

linear DNAlinear DNA.. causing latent infectionscausing latent infections ؟؟؟؟ The ability of pathogenic virus to lie dormant within The ability of pathogenic virus to lie dormant within

a cella cell .. The The fivefive important human pathogens are: important human pathogens are: herpes simplex virus types 1 herpes simplex virus types 1 herpes simplex virus types 2herpes simplex virus types 2 varicellavaricella--zoster virus zoster virus cytomegalovirus cytomegalovirus EpsteinEpstein--Barr virus Barr virus ((the cause of infectious the cause of infectious

mononucleosismononucleosis).).??!! ??!!

infectious mononucleosis characteristicinfectious mononucleosis characteristic : :Increase mononuclear WBC . Increase mononuclear WBC .

Atypical lymphocyte.Atypical lymphocyte.

Generalized lymphadenopathy . Generalized lymphadenopathy .

Splenomegaly. Splenomegaly.

Occasional hepatomegaly by hepatitis . Occasional hepatomegaly by hepatitis .

Poxviruses Poxviruses These are the These are the largestlargest viruses viruses bricklike shape bricklike shape an envelope with an unusual appearance an envelope with an unusual appearance complex capsid symmetry complex capsid symmetry they cause they cause skin lesions, or skin lesions, or ""pockspocks E.gE.g./ Smallpox virus ./ Smallpox virus

vaccinia virus (vaccinia virus (used in the smallpox used in the smallpox vaccinevaccine.. ) )

RNA Viruses RNA Viruses PicornavirusesPicornaviruses These are the These are the smallest smallest ((28 nm in 28 nm in

diameterdiameter) ) RNA virusesRNA viruses singlesingle--stranded, linear, nonsegmented, stranded, linear, nonsegmented,

positivepositive--polarity RNA within a naked polarity RNA within a naked icosahedral capsid icosahedral capsid

PicoPico (small), (small), RNARNA-containing -containing There are There are two groupstwo groups of human pathogens of human pathogens 1.1. enteroviruses enteroviruses : poliovirus, coxsackievirus, : poliovirus, coxsackievirus,

echovirus, and hepatitis A virus echovirus, and hepatitis A virus 2.2. rhinoviruses rhinoviruses

Caliciviruses Caliciviruses These are naked viruses These are naked viruses ((38 nm in 38 nm in

diameterdiameter) ) with an icosahedral capsid with an icosahedral capsid They have singleThey have single--stranded, linear, stranded, linear,

nonsegmented, positivenonsegmented, positive--polarity RNApolarity RNA.. There are two human pathogens There are two human pathogens

1.1. Norwalk Norwalk virus ?!virus ?!

2.2. hepatitis E virus hepatitis E virus

NoteNote// Taxonomists have recently placed hepatitis Taxonomists have recently placed hepatitis

E virus into its own genus called E virus into its own genus called hepevirushepevirus..

Norwalk Norwalk virusvirus ?! ?!

First isolated in 1968 from the stools of First isolated in 1968 from the stools of school children in Norwalk, Ohioschool children in Norwalk, Ohio who who were suffering fromwere suffering from gastroenteritisgastroenteritis . .

ReovirusesReoviruses These are naked viruses These are naked viruses ((75 nm in 75 nm in

diameterdiameter) ) with two icosahedral capsid with two icosahedral capsid coats coats

They have They have 1010 segments of double segments of double--stranded linear RNA stranded linear RNA

The name is an acronym of The name is an acronym of rrespiratory espiratory eenteric nteric oorphan rphan ؟؟.! .!

because they were originally found in the because they were originally found in the respiratory and enteric tracts and were not respiratory and enteric tracts and were not associated with any human disease associated with any human disease

E.g./E.g./rotavirus rotavirus diarrhea mainly in infants diarrhea mainly in infants

FlavivirusesFlaviviruses E.g./StE.g./St. . Louis and Japanese encephalitis Louis and Japanese encephalitis

viruses viruses Return to table . Return to table .

Togaviruses Togaviruses There are There are two majortwo major groups of human groups of human

pathogenspathogens:: 1.1. The alphavirus groupThe alphavirus group includes includes eastern eastern

and western encephalitis virusesand western encephalitis viruses 2.2. the rubivirusthe rubivirus group consists only of group consists only of

rubellarubella virus virus..

The young boy pictured here,

displayed the characteristic

maculopapular rash indicative of

rubella, otherwise known as

German measles, or 3-day measles

•Rubella is a respiratory viral infection characterized by mild respiratory symptoms and low-grade fever, followed by a

maculopapular rash lasting about 3 days

Birth defects if acquired by a pregnant womanBirth defects if acquired by a pregnant woman: : deafness, cataracts, heart defects, mental deafness, cataracts, heart defects, mental retardation, and liver and spleen damageretardation, and liver and spleen damage ((at at least a 20% chance of damage to the fetus if a least a 20% chance of damage to the fetus if a woman is infected early in pregnancywoman is infected early in pregnancy( (

rubella vaccine be given as part of the rubella vaccine be given as part of the MMR vaccineMMR vaccine ((protecting against measles, protecting against measles, mumps, and rubellamumps, and rubella). ). MMR is MMR is recommended at recommended at 12-15 months12-15 months ((not not earlierearlier) ) and a and a second dosesecond dose when the child when the child is is 4-6 years4-6 years old old ((before kindergarten or 1st before kindergarten or 1st gradegrade). ).

RetrovirusesRetroviruses The term The term ""retroretro" " pertains to the reverse pertains to the reverse

transcription of the RNA genome into transcription of the RNA genome into DNA DNA

There are There are two two medically important medically important groupsgroups: :

1.1. The The oncovirus grouponcovirus group, which contains the , which contains the sarcoma sarcoma and and leukemia virusesleukemia viruses, e, e..gg.., , human Thuman T--cell leukemia virus cell leukemia virus ((HTLVHTLV))

2.2. the the lentivirus lentivirus ("("slow virusslow virus") ") groupgroup, which , which includes includes ((HIVHIV) ) and certain animal and certain animal pathogens, epathogens, e..gg.., visna virus, visna virus..

Note/Note/ A third group, spumavirusesA third group, spumaviruses

Orthomyxoviruses Orthomyxoviruses The term The term ""myxomyxo"" refers to the affinity of refers to the affinity of

these viruses for these viruses for mucinsmucins ""orthoortho" " is added to distinguish them from is added to distinguish them from

the paramyxoviruses the paramyxoviruses Influenza virus is the main human Influenza virus is the main human

pathogen pathogen

Paramyxoviruses Paramyxoviruses The important human pathogens are The important human pathogens are

measles, mumpsmeasles, mumps, , parainfluenzaparainfluenza, and , and respiratory syncytial virusesrespiratory syncytial viruses..

This child’s face is displaying diffuse lymphedema of the neck due to a mumps virus infection of the parotid salivary glands

Measles is spread through respiration Measles is spread through respiration ((contact with fluids contact with fluids from an infected person's nose and mouth, either directly from an infected person's nose and mouth, either directly or through aerosol transmissionor through aerosol transmission)), and is highly , and is highly

contagiouscontagious..

RhabdovirusesRhabdoviruses These are bulletThese are bullet--shaped enveloped viruses shaped enveloped viruses

((""rhabdorhabdo" " refers to the refers to the bullet shapebullet shape ) )

RabiesRabies virus is the virus is the onlyonly important important humanhuman pathogen pathogen

This transmission electron micrograph (TEM) revealed the presence of numerous dark, bullet-shaped rabies virions within an infected tissue sample

FilovirusesFiloviruses The term The term ""filofilo" " means means ""threadthread" " and refers and refers

to the to the long filamentslong filaments They are They are highly pleomorphichighly pleomorphic, , long filaments that are 80 nm in diameter long filaments that are 80 nm in diameter

but can be thousands of nanometers but can be thousands of nanometers long long

The two human pathogens are The two human pathogens are

1.1. Ebola virus Ebola virus

2.2. Marburg virus Marburg virus

CoronavirusesCoronaviruses The term The term ""coronacorona" " refers to the prominent refers to the prominent

halo of halo of spikes protruding from the spikes protruding from the envelope envelope

Coronaviruses cause respiratory tract Coronaviruses cause respiratory tract infections in humans :infections in humans :

E.g./E.g./common coldcommon cold SARSSARS ( (severe acute respiratory syndromesevere acute respiratory syndrome) )

ArenavirusesArenaviruses The term The term ""arenaarena" " means means ""sandsand" " and and

refers to granules on the virion surface refers to granules on the virion surface that are that are nonfunctional ribosomes nonfunctional ribosomes

TwoTwo human pathogens are human pathogens are

1.1. lymphocytic choriomeningitis virus lymphocytic choriomeningitis virus

2.2. Lassa fever virus Lassa fever virus

BunyavirusesBunyaviruses Some bunyaviruses contain ambisense Some bunyaviruses contain ambisense

RNA in their genome RNA in their genome ) ) unusual genome unusual genome like like Arenaviruses) Arenaviruses)

The term The term ""bunyabunya" " refers to the prototype, refers to the prototype, Bunyamwera virus, which is named for Bunyamwera virus, which is named for the place in Africa where it was isolated the place in Africa where it was isolated

These viruses cause :These viruses cause : 1.1. encephalitis encephalitis 2.2. fevers such as Korean hemorrhagic fever fevers such as Korean hemorrhagic fever Hantaviruses, such as Sin Nombre virus Hantaviruses, such as Sin Nombre virus

are members of this family are members of this family

DeltavirusDeltavirus It is a It is a defective virusdefective virus because it cannot because it cannot

replicate unless hepatitis B virus replicate unless hepatitis B virus ((HBVHBV) ) is is present within the same cellpresent within the same cell..

The RNA genome of HDV encodes only The RNA genome of HDV encodes only one protein, the internal core protein called one protein, the internal core protein called delta antigen delta antigen soso

HBV is required because it encodes HBV is required because it encodes hepatitis B surface antigen hepatitis B surface antigen ((HBsAgHBsAg)), which , which serves as the outer serves as the outer protein coatprotein coat of HDV of HDV

Note/ Note/ Hepatitis deltaHepatitis delta virus virus ((HDVHDV) ) is the is the onlyonly member of this genus member of this genus

Virus FamilyVirus FamilyEnvelope Envelope PresentPresent

Capsid Capsid SymmetrySymmetry

Particle Particle Size Size ((nmnm

RNA MWRNA MW

((xx101066))

RNA RNA StructureStructure

Medically Medically Important Important

VirusesViruses

PicornavirusPicornavirusNoNoIcosahedralIcosahedral28282.52.5SS linear, SS linear, nonsegmenonsegmented, nted, positive positive polaritypolarity

Poliovirus, Poliovirus, rhinovirus, rhinovirus, hepatitis A hepatitis A virusvirus

CalicivirusCalicivirusNoNoIcosahedralIcosahedral38382.72.7SS linear, SS linear, nonsegmenonsegmented, nted, positive positive polaritypolarity

Norwalk Norwalk virus, virus, hepatitis E hepatitis E virusvirus

ReovirusReovirusNoNoIcosahedralIcosahedral75751515DS linearDS linear, , 10 10 segmentssegments

RotavirusRotavirus

FlavivirusFlavivirusYesYesIcosahedralIcosahedral454544SS linear, SS linear, nonsegmentnonsegmented, positive ed, positive polaritypolarity

Yellow fever Yellow fever virus, dengue virus, dengue virus, West virus, West Nile virus, Nile virus, hepatitis C hepatitis C virusvirus

Classification of RNA Viruses .

TogavirusTogavirusYesYesIcosahedralIcosahedral606044SS linear, SS linear, nonsegmented, nonsegmented, positive polaritypositive polarity

Rubella Rubella virusvirus

RetrovirusRetrovirusYesYesIcosahedralIcosahedral1001007722SS linear, 2 SS linear, 2 identical strands identical strands ((diploiddiploid)), positive , positive polaritypolarity

HIV, HIV, human Thuman T--cell cell leukemia leukemia virusvirus

OrthomyxovirusOrthomyxovirusYesYesHelicalHelical80–80–120120

44SS linear, 8 SS linear, 8 segments, segments, negative polaritynegative polarity

Influenza Influenza virusvirus

ParamyxovirusParamyxovirusYesYesHelicalHelical15015066SS linear, SS linear, nonsegmented, nonsegmented, negative polaritynegative polarity

Measles Measles virus, virus, mumps mumps virus, virus, respiratory respiratory syncytial syncytial virusvirus

RhabdovirusRhabdovirusYesYesHelicalHelical75 75 xx 180180

44SS linear, SS linear, nonsegmented, nonsegmented, negative polaritynegative polarity

Rabies Rabies virusvirus

FilovirusFilovirusYesYesHelicalHelical80803344SS linear, SS linear,

nonsegmented, nonsegmented, negative polaritynegative polarity

Ebola virus, Ebola virus, Marburg Marburg virusvirus

CoronavirusCoronavirusYesYesHelicalHelical1001001010SS linear, SS linear, nonsegmented, nonsegmented, positive polaritypositive polarity

CoronavirusCoronavirus

ArenavirusArenavirusYesYesHelicalHelical80–13080–13055SS circular, 2 SS circular, 2 segments with segments with cohesive ends, cohesive ends, negative negative polaritypolarity

Lymphocytic Lymphocytic choriomeninchoriomeningitis virusgitis virus

BunyavirusBunyavirusYesYesHelicalHelical10010055SS circular, 3 SS circular, 3 segments with segments with cohesive cohesive ends, negative ends, negative polaritypolarity

California California encephalitiencephalitis virus, s virus, hantavirushantavirus

DeltavirusDeltavirusYesYesUncertainUncertain 37370.50.5SS circular, SS circular, closed circle, closed circle, negative negative polaritypolarity

Hepatitis Hepatitis delta virusdelta virus