Classification of Medically Important Viruses Prepared by Mohammed

Classification of Medically Important Viruses Prepared by : - Mohammed Osama El-Ifranji

Introduction § The classification of viruses is based on chemical and morphologic criteria. § The two major components of the virus used in classification are -: 1. The nucleic acid (its molecular weight and structure) 2. the capsid (its size and symmetry and whether it is enveloped).

Classification of DNA Viruses Virus Family Envelope Capsid Present Symmetry Particle size (nm) DNA MW (x 106) DNA Structure Medically Important Viruses Parvovirus No Icosahedral 22 2 SS, linear B 19 virus Papovavirus No Icosahedral 55 5– 3 DS, circular, supercoiled Papillomavirus Adenovirus No Icosahedral 75 23 DS, linear Adenovirus Hepadnavirus Yes Icosahedral 42 1. 5 DS, incomplete circular Hepatitis B virus Herpesvirus Yes Icosahedral 100 – 100 150 DS, linear Herpes simplex virus, varicellazoster virus, cytomegaloviru s, Epstein-Barr virus Poxvirus Yes Complex 250 x 400 – 125 185 DS, linear Smallpox virus, vaccinia virus

DNA Viruses Parvoviruses § These are very small (22 nm in diameter) § naked icosahedra viruses with single-stranded linear DNA. § There are two types of parvoviruses -: 1. The defective parvoviruses. § e. g. , adeno-associated virus § require a helper virus for replication § The DNA of defective parvoviruses is unusual because plus-strand DNA and minus-strand DNA are carried in separate particles.

2. The nondefective parvoviruses § best illustrated by B 19 virus which associated with : v aplastic crises in sickle cell anemia patients v erythema infectiosum ? !! childhood disease characterized by a "slapped-cheeks" rash, fever , headach and rash in (face, trunk, extremities ) Note / may confused with rubella.

Papovaviruses § These are naked icosahedra viruses (55 nm in diameter) § double-stranded circular supercoiled DNA § "papova" is an acronym of papilloma, polyoma, and simian vacuolating viruses § Three human papovaviruses : 1. JC virus progressive multifocal leukoencephalopathy 2. BK virus : from the urine of immunosuppressed kidney transplant patients 3. human papillomavirus. Note/Polyomavirus (mice ), simian vacuolating virus 40 (monkeys ) induce malignant tumors

Adenoviruses § These are naked icosahedral viruses (75 nm in diameter) § double-stranded linear DNA. § There at least 40 antigenic types § some of which cause sarcomas in animals but no tumors in humans. Note/ They cause pharyngitis, upper and lower respiratory tract disease

Hepadnaviruses § These are double-shelled viruses (42 nm in diameter) § an icosahedral capsid covered by an envelope § The DNA is a double-stranded circle that is unusual ؟؟ because the complete strand is not a covalently closed circle and the other strand is missing approximately 25% of its length. e. g. /Hepatitis B virus (human)

Herpesviruses § These are enveloped viruses (100 nm in diameter) § icosahedra nucleocapsid and double-stranded linear DNA. § causing latent infections ؟؟ The ability of pathogenic virus to lie dormant within a cell. § The five important human pathogens are: 1. herpes simplex virus types 1 2. herpes simplex virus types 2 3. varicella-zoster virus 4. cytomegalovirus 5. Epstein-Barr virus (the cause of infectious mononucleosis). ? ? !!

infectious mononucleosis characteristic : v. Increase mononuclear WBC. v. Atypical lymphocyte. v. Generalized lymphadenopathy. v. Splenomegaly. v. Occasional hepatomegaly by hepatitis.

Poxviruses § These are the largest viruses § bricklike shape § an envelope with an unusual appearance § complex capsid symmetry § they cause skin lesions, or "pocks § E. g. / Smallpox virus vaccinia virus (used in the smallpox vaccine. )

RNA Viruses Picornaviruses § These are the smallest )28 nm in diameter) RNA viruses § single-stranded, linear, nonsegmented, positive-polarity RNA within a naked icosahedral capsid § Pico (small), RNA-containing § There are two groups of human pathogens 1. enteroviruses : poliovirus, coxsackievirus, echovirus, and hepatitis A virus 2. rhinoviruses

Caliciviruses § These are naked viruses (38 nm in diameter) with an icosahedral capsid § They have single-stranded, linear, nonsegmented, positive-polarity RNA. § There are two human pathogens 1. Norwalk virus ? ! 2. hepatitis E virus Note/ Taxonomists have recently placed hepatitis E virus into its own genus called hepevirus.

Norwalk virus ? ! First isolated in 1968 from the stools of school children in Norwalk, Ohio who were suffering from gastroenteritis.

Reoviruses § These are naked viruses (75 nm in diameter) with two icosahedral capsid coats § They have 10 segments of doublestranded linear RNA § The name is an acronym of respiratory enteric orphan !. ؟ because they were originally found in the respiratory and enteric tracts and were not associated with any human disease § E. g. /rotavirus diarrhea mainly in infants

Flaviviruses § E. g. /St. Louis and Japanese encephalitis viruses § Return to table. Togaviruses § There are two major groups of human pathogens: 1. The alphavirus group includes eastern and western encephalitis viruses 2. the rubivirus group consists only of rubella 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 lowgrade fever, followed by a maculopapular rash lasting about 3 days

§ Birth defects if acquired by a pregnant woman: deafness, cataracts, heart defects, mental retardation, and liver and spleen damage (at least a 20% chance of damage to the fetus if a woman is infected early in pregnancy ) § rubella vaccine be given as part of the MMR vaccine (protecting against measles, mumps, and rubella). MMR is recommended at 12 -15 months (not earlier) and a second dose when the child is 4 -6 years old (before kindergarten or 1 st grade).

Retroviruses § The term "retro" pertains to the reverse transcription of the RNA genome into DNA § There are two medically important groups: 1. The oncovirus group, which contains the sarcoma and leukemia viruses, e. g. , human T-cell leukemia virus (HTLV) 2. the lentivirus ("slow virus") group, which includes (HIV) and certain animal pathogens, e. g. , visna virus. Note/ A third group, spumaviruses

Orthomyxoviruses § The term "myxo" refers to the affinity of these viruses for mucins § "ortho" is added to distinguish them from the paramyxoviruses § Influenza virus is the main human pathogen

Paramyxoviruses § The important human pathogens are measles, mumps, parainfluenza, and respiratory 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 (contact with fluids from an infected person's nose and mouth, either directly or through aerosol transmission), and is highly contagious.

Rhabdoviruses § These are bullet-shaped enveloped viruses ("rhabdo "refers to the bullet shape ) § Rabies virus is the only important human pathogen This transmission electron micrograph (TEM) revealed the presence of numerous dark, bullet-shaped rabies virions within an infected tissue sample

Filoviruses § The term "filo "means "thread "and refers to the long filaments § They are highly pleomorphic, § long filaments that are 80 nm in diameter but can be thousands of nanometers long § The two human pathogens are 1. Ebola virus 2. Marburg virus

Coronaviruses § The term "corona" refers to the prominent halo of spikes protruding from the envelope § Coronaviruses cause respiratory tract infections in humans : E. g. /common cold SARS) severe acute respiratory syndrome)

Arenaviruses § The term "arena "means "sand" and refers to granules on the virion surface that are nonfunctional ribosomes § Two human pathogens are 1. lymphocytic choriomeningitis virus 2. Lassa fever virus

Bunyaviruses § Some bunyaviruses contain ambisense RNA in their genome (unusual genome like Arenaviruses) § The term "bunya" refers to the prototype, Bunyamwera virus, which is named for the place in Africa where it was isolated § These viruses cause : 1. encephalitis 2. fevers such as Korean hemorrhagic fever § Hantaviruses, such as Sin Nombre virus are members of this family

Deltavirus § It is a defective virus because it cannot replicate unless hepatitis B virus (HBV) is present within the same cell. § The RNA genome of HDV encodes only one protein, the internal core protein called delta antigen so HBV is required because it encodes hepatitis B surface antigen (HBs. Ag), which serves as the outer protein coat of HDV Note/ Hepatitis delta virus (HDV) is the only member of this genus

. Classification of RNA Viruses Virus Family Envelope Present Capsid Particle Symmetry Size (nm RNA MW (610 x) RNA Structure Medically Important Viruses Picornavirus No Icosahedral 28 2. 5 SS linear, nonsegme nted, positive polarity Poliovirus, rhinovirus, hepatitis A virus Calicivirus No Icosahedral 38 2. 7 SS linear, nonsegme nted, positive polarity Norwalk virus, hepatitis E virus Reovirus No Icosahedral 75 15 DS linear, 10 segments Rotavirus Flavivirus Yes Icosahedral 4 SS linear, nonsegment ed, positive polarity Yellow fever virus, dengue virus, West Nile virus, hepatitis C virus 45

Togavirus Yes Icosahedral Retrovirus Yes Orthomyxovirus 60 4 SS linear, nonsegmented, positive polarity Rubella virus Icosahedral 100 27 SS linear, 2 identical strands (diploid), positive polarity HIV, human Tcell leukemia virus Yes Helical – 80 120 4 SS linear, 8 segments, negative polarity Influenza virus Paramyxovirus Yes Helical 150 6 SS linear, nonsegmented, negative polarity Measles virus, mumps virus, respiratory syncytial virus Rhabdovirus Yes Helical 75 x 180 4 SS linear, nonsegmented, negative polarity Rabies virus Filovirus Yes Helical 380 4 SS linear, nonsegmented, negative polarity Ebola virus, Marburg virus

Coronavirus Yes Helical 100 10 SS linear, nonsegmented, positive polarity Coronavirus Arenavirus Yes Helical 130– 80 5 SS circular, 2 segments with cohesive ends, negative polarity Lymphocytic choriomenin gitis virus Bunyavirus Yes Helical 100 5 SS circular, 3 segments with cohesive ends, negative polarity California encephaliti s virus, hantavirus Deltavirus Uncertain 37 0. 5 SS circular, closed circle, negative polarity Hepatitis delta virus Yes