1. Viruses, Viroids, and Prions
Chapter 13, part B
Viruses, Viroids, and Prions

2. Attachment, Penetration, and Uncoating
Figure 13.14

3. Release of an enveloped virus by budding
Figure 13.20

4. Multiplication of DNA Virus
Papovavirus 1
Virion attaches to host cell 7
Virions are released
Host cell
DNA
Capsid
DNA 2
Virion penetrates cell and its DNA is uncoated 6
Virions mature
Cytoplasm
Capsid proteins
mRNA 5
Late translation; capsid proteins are synthesized 3
Early transcription and translation; enzymes are synthesized 4
Late transcription; DNA is replicated
Figure 13.15

5. Pathways of Multiplication for RNA-Containing Viruses
Figure 13.17

6. Multiplication of a Retrovirus
Reverse transcriptase
Capsid
DNA
Virus
Two identical + stands of RNA 1
Retrovirus penetrates host cell.
Host cell
DNA of one of the host cell’s chromosomes 5
Mature retrovirus leaves host cell, acquiring an envelope as it buds out.
Reverse transcriptase 2
Viral RNA
Virion penetrates cell and its DNA is uncoated
Identical strands of RNA 4
Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins.
Viral proteins
RNA 3
The new viral DNA is tranported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA.
Provirus
Figure 13.19

7. Cancer
Activated oncogenes transform normal cells into cancerous cells.
Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens.
The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

8. Oncogenic Viruses Oncogenic DNA Viruses Adenoviridae Heresviridae
Poxviridae
Papovaviridae
Hepadnaviridae
Oncogenic RNA viruses
Retroviridae
Viral RNA is transcribed to DNA which can integrate into host DNA
HTLV 1
HTLV 2

9. Latent Viral Infections
Virus remains in asymptomatic host cell for long periods
Cold sores, shingles
Persistent Viral Infections
Disease processes occurs over a long period, generally fatal
Subacute sclerosing panencephalitis (measles virus)

10. Prions Infectious proteins
Inherited and transmissible by ingestion, transplant, & surgical instruments
Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease
PrPC, normal cellular prion protein, on cell surface
PrPSc, scrapie protein, accumulate in brain cells forming plaques

11. Prions
PrPSc
PrPc 1 2 3 4
Lysosome
Endosome 5 6 7 8
Figure 13.21

12. Plant viruses enter through wounds or via insects
Viroids
Viroids are infectious RNA; potato spindle tuber disease
Figure 13.22

13. Some Plant Viruses
Table 13.6

14. Virus Families Single-stranded DNA, nonenveloped viruses Parvoviridae
Human parvovirus
Fifth disease
Anemia in immunocompromised patients

15. Double-stranded DNA, nonenveloped viruses
Mastadenovirus
Respiratory infections in humans
Tumors in animals

16. Double-stranded DNA, nonenveloped viruses
Papillomavirus (human wart virus)
Polyomavirus
Cause tumors, some cause cancer

17. Double-stranded DNA, nonenveloped viruses
Orthopoxvirus (vaccinia and smallpox viruses)
Molluscipoxvirus
Smallpox, molluscum contagiosum, cowpox

18. Double-stranded DNA, nonenveloped viruses
Simplexvirus (HHV1 and HHV 2)
Varicellavirus (HHV 3)
Lymphocryptovirus (HHV 4)
Cytomegalovirus (HHV 5)
Roseolovirus (HHV 6)
HHV 7
Kaposi's sarcoma (HHV 8)
Some herpesviruses can remain latent in host cells

19. Double-stranded DNA, nonenveloped viruses
Hepadnavirus (Hepatitis B virus)
Use reverse transcriptase to produce DNA from mRNA

20. Single-stranded RNA, + strand, nonenveloped
Enterovirus
Enteroviruses include poliovirus and coxsackievirus
Rhinovirus
Hepatitis A virus

21. Single-stranded RNA, + strand, nonenveloped
Hepatitis E virus
Norovirus (Norwalk agent) causes gastroenteritis

22. Single-stranded RNA, + strand, nonenveloped
Alphavirus
Alphaviruses are transmitted by arthropods; include EEE, WEE
Rubivirus (rubella virus)

23. Single-stranded RNA, + strand, nonenveloped
Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses
Hepatitis C virus

24. Single-stranded RNA, + strand, nonenveloped
Coronavirus
Upper respiratory infections

25. Single-stranded RNA, – strand, one RNA strand
Vesiculovirus
Lyssavirus (rabies virus)
Cause numerous animal diseases

26. Single-stranded RNA, – strand, one RNA strand
Filovirus
Enveloped, helical viruses
Ebola and Marburg viruses

27. Single-stranded RNA, – strand, one RNA strand
Paramyxovirus
Morbillivirus
Paramyxovirus causes parainfluenza, mumps and Newcastle disease

28. Single-stranded RNA, – strand, one RNA strand
Hepatitis D virus
Depends on coinfection with Hepadnavirus

29. Single-stranded RNA, – strand, multiple RNA strands
Influenzavirus (Influenza viruses A and B)
Influenza C virus
Envelope spikes can agglutinate RBCs

30. Single-stranded RNA, – strand, multiple RNA strands
Bunyavirus (CE virus)
Hantavirus

31. Single-stranded RNA, – strand, multiple RNA strands
Arenavirus
Helical capsids contain RNA-containing granules
Lymphocytic choriomeningitis
VEE and Lassa Fever

32. Single-stranded RNA, two RNA strands, produce DNA
Lentivirus (HIV)
Oncogenic viruses
Use reverse transcriptase to produce DNA from viral genome
Includes all RNA tumor viruses

33. Double-stranded RNA, nonenveloped
Reovirus (Respiratory Enteric Orphan)
Rotavirus
Mild respiratory infections and gastroenteritis
Colorado tick fever