1. Viruses, Viroids, and Prions13
Viruses, Viroids, and Prions

2. Attachment, Penetration, and Uncoating
Pinocytosis
Figure 13.14a

3. Attachment, Penetration, and Uncoating
Fusion
Figure 13.14b

4. Release of an Enveloped Virus by Budding
Figure 13.20

5. Multiplication of DNA Virus
Figure 13.15

6. + Sense Strand (+ Strand) RNA Virus
Maturation
and release
Entry
and uncoating
Translation and synthesis
of viral proteins
RNA replication by viral RNA-
dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
Nucleus
Attachment
Viral
protein
Capsid
Cytoplasm
Host cell
– strand is transcribed
from + viral genome.
+ strand
mRNA is transcribed
from the – strand.
RNA
genome
(RNA)
ssRNA; +
or sense strand;
Picornaviridae
(a)
Figure 13.17a

7. — Antisense Strand (— Strand) RNA Virus
Maturation
and release
Entry
and uncoating
Translation and synthesis
of viral proteins
RNA replication by viral RNA-
dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
Nucleus
Attachment
Viral
protein
Capsid
Cytoplasm
Host cell
– strands are
incorporated
into capsid
The + strand (mRNA) must first
be transcribed from the – viral
genome before proteins can
be synthesized.
Additional – strands are
transcribed from mRNA.
RNA
genome
(RNA)
ssRNA; – or
antisense strand;
Rhabdoviridae
(b)
Figure 13.17b

8. Double-Stranded RNA Virus
Maturation
and release
Entry
and uncoating
Translation and synthesis
of viral proteins
RNA replication by viral RNA-
dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
Nucleus
Attachment
Viral
protein
RNA polymerase initiates production of
– strands. The mRNA and – strands form the
dsRNA that is incorporated as new viral genome.
Cytoplasm
Host cell
mRNA is produced inside the
capsid and released into the
cytoplasm of the host.
Capsid
RNA
genome
(RNA)
dsRNA; + or sense
strand with – or
antisense strand;
Reoviridae
Capsid proteins and RNA-
(c)
Figure 13.17c

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

10. Multiplication of a Retrovirus
PLAY
Animation: Viral Replication
Figure 13.19

11. DNA and RNA Viruses Compared
DNA: Cellular enzyme transcribes viral DNA in nucleus.
DNA, reverse transcriptase: Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA.
RNA, + strand: Viral RNA is a template for synthesis of RNA polymerase.

12. DNA and RNA Viruses Compared
RNA – strand: Viral enzyme copies viral RNA to make mRNA in cytoplasm.
RNA, double-stranded: Viral enzyme copies – strand RNA to make mRNA in cytoplasm.
RNA, reverse transcriptase: Viral enzyme copes viral RNA to make DNA in cytoplasm.

13. 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.

14. 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

15. Latent viral infections
Virus remains in asymptomatic host cell for long periods.
Cold sores, shingles
Presistent viral infections
Disease processes occurs over a long period; generally is fatal.
Subacute sclerosing panencephalitis (measles virus)
Figure 13.21

16. Prions Infectious proteins
Inherited and transmissible by ingestion, transplant, and 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; accumulates in brain cells forming plaques
PLAY
Animation: Prion Reproduction

17. Prions
Figure 13.22

18. Plant viruses: Enter through wounds or via insects.
Viroids: Infectious RNA; e.g., potato spindle tuber disease.
Figure 13.23

19. Some Plant Viruses
Table 13.6

20. Virus Families Single-stranded DNA, nonenveloped viruses Parvoviridae
Human parvovirus
Fifth disease
Anemia in immunocompromised patients
Table 13.2 (1 of 20)

21. Double-Stranded DNA, Nonenveloped Viruses
Mastadenovirus
Respiratory infections in humans
Tumors in animals
Table 13.2 (2 of 20)

22. Double-Stranded DNA, Nonenveloped Viruses
Papillomavirus (human wart virus)
Polyomavirus
Cause tumors; some cause cancer
Table 13.2 (3 of 20)

23. Double-Stranded DNA, Enveloped Viruses
Orthopoxvirus (vaccinia and smallpox viruses)
Molluscipoxvirus
Smallpox
Molluscum contagiosum
Cowpox
Table 13.2 (4 of 20)

24. Double-Stranded DNA, Enveloped 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.
Table 13.2 (5 of 20)

25. Double-Stranded DNA, Enveloped Viruses
Hepadnavirus (Hepatitis B virus)
Use reverse transcriptase to produce DNA from mRNA.
Table 13.2 (6 of 20)

26. Single-Stranded RNA, + Strand, Nonenveloped
Enterovirus
Enteroviruses include poliovirus and coxsackievirus.
Rhinovirus
Hepatitis A virus
Table 13.2 (7 of 20)

27. Single-Stranded RNA, + Strand, Nonenveloped
Hepatitis E virus
Norovirus causes gastroenteritis.
Table 13.2 (8 of 20)

28. Single-Stranded RNA, + Strand, Enveloped
Alphavirus
Alphaviruses are transmitted by arthropods; include EEE, WEE.
Rubivirus (rubella virus)
Table 13.2 (9 of 20)

29. Single-Stranded RNA, + Strand, Enveloped
Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses
Hepatitis C virus
Table 13.2 (10 of 20)

30. Single-Stranded RNA, + Strand, Enveloped
Coronavirus
Upper respiratory infections
SARS
Table 13.2 (11 of 20)

31. Single-Stranded RNA, – Strand, One RNA Strand
Vesiculovirus
Lyssavirus (rabies virus)
Cause numerous animal diseases
Table 13.2 (12 of 20)

32. Single-Stranded RNA, – Strand, One RNA Strand
Filovirus
Enveloped, helical viruses
Ebola and Marburg viruses
Table 13.2 (13 of 20)

33. Single-Stranded RNA, – Strand, One RNA Strand
Paramyxovirus
Morbillivirus
Parainfluenza
Mumps
Newcastle disease
Table 13.2 (14 of 20)

34. Single-Stranded RNA, – Strand, One RNA Strand
Hepatitis D virus
Depends on coinfection with Hepadnavirus
Table 13.2 (15 of 20)

35. Single-Stranded RNA, – Strand, Multiple RNA Strands
Influenzavirus (Influenza viruses A and B)
Influenza C virus
Envelope spikes can agglutinate RBCs.
Table 13.2 (16 of 20)

36. Crossing the Species Barrier
UN 13.3

37. Single-Stranded RNA, – Strand, Multiple RNA Strands
Bunyavirus (CE virus)
Hantavirus
Table 13.2 (17 of 20)

38. Single-Stranded RNA, – Strand, Multiple RNA Strands
Arenavirus
Helical capsids contain RNA-containing granules
Lymphocytic choriomeningitis
VEE and Lassa Fever
Table 13.2 (18 of 20)

39. 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
Table 13.2 (19 of 20)

40. Double-Stranded RNA, Nonenveloped
Reovirus (Respiratory Enteric Orphan)
Rotavirus
Mild respiratory infections and gastroenteritis
Colorado tick fever
Table 13.2 (20 of 20)