1. Classification of Medically Important Viruses @ Two components of virus are used in classification : 1. Molecular weight & structure of nucleic acid 2. Size, symmetry,& envelope of capsid

2. DNA VIRUSES 1. 3 nonenveloped, icosahedral virus families:*parvoviruses, *papovaviruses, *adenoviruses 2. 3 enveloped virus families : a) hepadnavirus family, eg : hepatitis B virus – icosahedral b) herpesviruses - icosahedral. c) pox viruses - complex symmetry

3. Papovaviruses @ Nonenveloped (naked) icosahedral viruses, with double-stranded circular DNA. @ Known: papilloma, polyoma, simian viruses @ 3 human papovaviruses known : 1.JC virus, isolated from progressive multifocal leukoencephalopathy cases. 2.BK virus, isolated from urine of kidney transplant patients. 3.Human papillomavirus

4. Adenoviruses @ Naked icosahedral, Ds. linear DNA viruses @ Cause pharyngitis, URT & LRT diseases. @ There are at least 40 antigenic types.

5. Parvoviruses @ Very small, nonenveloped, icosahedral, Ss., linear DNA. @ 2 types of parvoviruses: Defective & nondefective : Defective require a helper virus for replication. Nondefective,e.g. B 19 virus

6. Hepadnaviruses @ These are double-stranded viruses with an icosahedral capsid covered by an envelope. @ Hepatitis B virus is the human pathogen in this family.

7. Herpesviruses @ Enveloped, icosahedral, Ds., linear DNA viruses @ Cause latent infections. @ The 5 important pathogens: *herpes simplex types I & 2, *varicella-zoster, *CMV *Epstein-Barr cause of IM.

8. Poxviruses @ Largest virus with a bricklike shape, an envelope, & a complex capsid symmetry. @ Cause skin lesions, or "pocks" @ Smallpox & vaccinia are the two important members. @ Vaccinia virus is used in smallpox vaccine.

9. RNA VIRUSES @ 14 families of RNA viruses. @ 3 naked icosahedral viruses : 1. Picornavirus 2. Calicivirus 3. Reovirus @ 3 enveloped icosahedral viruses: 1. Flavivirus 2. Togavirus 3. Retrovirus

10. @ 8 are enveloped helical viruses: * 5 have Ss. linear RNA, e.g: (1) orthomyxovirus (2) paramyxovirus (3) rhabdovirus (4) filovirus (5) coronavirus * 3 have Ss. circular RNA, e.g: (1) arenavirus (2) bunyavirus (3) deltavirus.

11. Picornaviruses @ The smallest RNA viruses. @ Have Ss, linear, nonsegmented RNA within a naked icosahedral capsid. @ "picorna" is derived from pico- small @ Divided into 2 groups of pathogens: (I) enteroviruses : poliovirus, echovirus coxsackievirus, hepatitis A (2) rhinoviruses.

12. Caliciviruses @ Naked, icosahedral viruses. @ Have Ss, linear, nonsegmented, RNA. @ 2 human pathogens: * Norwalk virus * hepatitis E virus.

13. Reoviruses @ Naked viruses with 2 icosahedral capsid coats. @ Have 10 segments of Ds. linear RNA. @ Main pathogen is rotavirus, causing diarrhea in infants.

14. Flaviviruses @ Enveloped, icosahedral, Ss, linear, nonsegmented, RNA viruses @ Include : hepatitis C virus, yellow fever virus, dengue virus, St. Louis encephalitis viruses. Japanese encephalitis viruses.

15. Togaviruses @ Enveloped, icosahedral, Ss, linear, nonsegmented RNA viruses @ 2 groups of human pathogens: * Alphaviruses: include : eastern & western encephalitis viruses * Rubiviruses: contain only rubella virus

16. Retroviruses @ Enveloped, icosahedral, with 2 strands of Ss, linear RNA viruses @ "retro" pertains to the reverse transcription of RNA into DNA. @ 2 medically important groups: 1.oncovirus group, contains the sarcoma & leukemia viruses, e.g. (human T cell leukemia virus-HTLV) 2.lentivirus group includes human immunodeficiency virus (HIV).

17. Orthomyxoviruses @ Enveloped, with a helical capsid & 8 segments of linear, Ss RNA. @ "myxo" means affinity for mucins. @ Influenza virus is the main human pathogen.

18. Paramyxoviruses @ Enveloped, helical, Ss, linear, non segmented RNA viruses @ Human pathogens are : *measles, *mumps, *parainfluenza, *respiratory syncytial (RSV).

19. Rhabdoviruses @ Bullet-shaped enveloped viruses with a helical, Ss, linear, nonsegmented RNA viruses @"rhabdo" refers to bullet shape. @ Rabies virus is the only important human pathogen.

20. Filoviruses @ Enveloped, helical, Ss, linear, nonsegmented RNA viruses. @ Pleomorphic, long filaments. @ "filo" means "thread". @ 2 human pathogens are : *Ebola virus *Marburg virus.

21. Coronaviruses @ Enveloped, helical, Ss, linear, nonsegmented RNA viruses. @ "corona" refers to crown of spikes protruding from envelope. @ Cause respiratory tract infections (e.g. common cold).

22. Arenaviruses @ Enveloped, helical, Ss, circular, 2 segments RNA viruses @ "arena" is "sand“, refers to ribosome granules on virus surface @ 2 human pathogens are known : *lymphocytic choriomeningitis virus *Lassa fever virus.

23. Bunyaviruses @ Enveloped, helical, Ss, circular 3 segments RNA viruses. @ "bunya" refers to the place in Africa where it was isolated. @ Cause encephalitis & fevers e.g Korean hemorrhagic fever.

24. Deltavirus @ Hepatitis delta virus (HDV) is the only member of this genus. @ Enveloped, helical, circular, Ss, RNA virus @ It is a defective virus “cannot replicate unless hepatitis B virus (HBV) is present within the same cell”