1. Chapter 10 Viruses Viruses contain DNA or RNA
And a protein coat called a
The capsid is composed of individual
Some are enclosed by an envelope
May have spikes protruding from envelope

2. Most viruses infect only specific types of cells in one host
Host range is determined by specific host attachment sites and cellular factors

3. Viruses

4. Polyhedral Viruses

5. Helical Viruses
Causes systemic infection often with hemorrhagic fever

6. Complex Viruses

7. Viral Taxonomy Family names end in -viridae Genus names end in -virus
A group of viruses sharing the same genes and host. Common names are used for species
Subspecies are designated by a number

8. Viral Taxonomy Family : Herpesviridae Genus: Simplexvirus
Species/Subspecies: Human herpes virus 1, HHV 2
Family: Retroviridae
Genus: Lentivirus
Species/Subspecies: Human Immunodeficiency Virus 1, HIV 2

9. Growing Animal Viruses
Animal viruses may be grown
in living animals
In embryonated eggs
or in cell culture.

10. Growing Viruses
Animal (and plant) viruses may be grown in cell culture.
For research purposes
For clinical identification of virus type
By observing

11. Virus Identification Some cytopathic effects (not comfirmatory)
Inclusion bodies - rabies virus
Syncytia formation – measles, common cold
Transformation – human papillomavirus

12. Virus Identification Serological tests
Detect antibodies against viruses in a patient
Use antibodies to identify viruses
Western blot
Viral nucleic acids: RFLPs (i.e. DNA Fingerprinting), PCR tests

13. Virus Identification – a cytopathic effect

14. Viral Multiplication
Viruses require host cell “machinery” for replication
Some viruses have some of their own enzymes: mainly for viral nucleic acid replication
Most, if not all, enzymes come from host cell
These enzymes are involved in building new virions

15. Multiplication of Bacteriophages (Lytic Cycle)
Phage causes lysis and death of host cell
Attachment Phage attaches by tail fibers to host cell
Penetration Phage lysozyme opens cell wall; DNA is then “injected” into cell
Biosynthesis Production of phage DNA and proteins
Maturation Assembly of phage particles
Release Phage lysozyme breaks cell wall

16. 1 2 3 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid
Sheath
Tail fiber 1
Attachment: Phage attaches to host cell.
Tail
Base plate
Pin
Cell wall
Plasma membrane 2
Penetration: Phage penetrates host cell and injects its DNA.
Sheath contracted
Tail core 3
Biosynthesis: phage DNA directs synthesis of viral components by host cell.

17. 4 5 Tail DNA Maturation: Viral components are assembled into virions.
Capsid 5
Release: Host cell lyses and new virions are released.
Tail fibers

18. The Lysogenic Cycle: Phage DNA incorporated into host DNA

19. Specialized Transduction
gal gene
Prophage
Bacterial DNA 1
Prophage exists in galactose-using host (containing the gal gene).
Galactose-positive donor cell
gal gene 2
Phage genome excises, carrying with it the adjacent gal gene from the host. 3
Phage matures and cell lyses, releasing phage carrying gal gene.
gal gene 4
Phage infects a cell that cannot utilize galactose (lacking gal gene).
Galactose-negative recipient cell 5
Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 6
Lysogenic cell can now metabolize galactose.
Galactose-positive recombinant cell

20. Multiplication of Animal viruses
Attachment Viruses attach to cell membrane
Penetration By endocytosis or fusion
Uncoating By viral or host enzymes
Biosynthesis Production of nucleic acid and proteins
Maturation Nucleic acid and capsid proteins assemble
Release By budding (enveloped viruses) or rupture (non-enveloped viruses)

21. Attachment, Penetration, and Uncoating

22. Release of an enveloped virus by budding

23. Nonenveloped DNA virus
Can cause cancer (cervical cancer)
Hand warts
Genital warts
Commonly sexually transmitted
Prevention: vaccine for HPV
Respiratory infections in humans
Usually sudden onset and short duration
Tumors in animals

24. Enveloped DNA virus Can cause chronic liver disease
Can lead to liver cancer
Body fluid transmisson
Prevention: vaccine
Human Herpes Virus 1 and HHV 2 – “cold sores” and genital herpes
Sexually transmitted
Other direct contact transmission
Prevention: condoms (not 100%), abstinence

25. Enveloped DNA virus Varicella-Zoster virus (HHV 3) –
Chicken pox is initial infection
Shingles may occur later
Contracted by inhaling virus
Prevention: vaccine
Epstein-Barr virus (HHV 4) – Infectious Mononucleosis
Saliva transmission
Burkitt’s lymphoma in African children
Prevention: avoid infected body fluids (mainly saliva)

26. Multiplication of a Retrovirus
Reverse transcriptase
Capsid
Envelope
Virus
Two identical strands 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
Its RNA is uncoated; reverse transcription takes place.
Identical strands of RNA
Viral 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

27. Retroviruses – enveloped RNA viruses
Use reverse transcriptase to produce DNA from RNA viral genome
HIV - AIDS
Oncogenic viruses
Some retroviruses can cause cancer

28. Cancer
The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.
“transform” normal cells into cancerous cells.
An oncovirus can promote oncogene expression
may contain oncogenes

29. Viral Infections
Virus remains in host cell for long periods, asymptomatically
Subsequent activation may lead to: i.e. cold sores, shingles
Persistent Viral Infections
Disease progresses over a long period, generally fatal
Subacute sclerosing panencephalitis, SSPE (measles virus)
AIDS dementia complex (HIV)

30. Prions Infectious proteins
Inherited, and transmissible by ingestion, transplant, & surgical instruments
Spongiform encephalopathies (fatal): Sheep Scrapie, Creutzfeldt-Jakob disease, mad cow disease
Cause:
normal cellular prion protein on cell surface,
converts to
scrapie protein, accumulates in brain cells forming plaques

31. Prions
PrPSc
PrPc 1 2 3 4
Lysosome
Endosome 5 6 7 8

32. Plant viruses and viroids
enter through wounds or via insects
are infectious RNA
One causes potato spindle tuber disease
Potato Spindle Tuber Viroids

33. RNA virus, nonenveloped
Poliovirus
May be paralytic in ~1% of cases
Transmission:
Prevention: vaccine
Human
Number one cause of the common cold
Attacks liver, kidneys, spleen
Transmission: fecal-oral route
Usually not fatal
Prevention: vaccine (long-term), immune globulin (short-term)

34. RNA virus, enveloped Influenza viruses A, B, and C Type A have caused
Both type A and B cause seasonal flu
Subtypes differ based on H and N spike variation

35. Influenza viruses continued:
Mutation of H and N spike can lead to epidemics or pandemics
Contracted by inhaling virus
Prevention: vaccine may prevent

36. RNA virus, enveloped Infects birds and humans Transmitted by mosquitos
First appeared in U.S. in 1999 in NYC area; now coast to coast
Symptoms: Usually “flu-like;” less than 1% get West Nile Encephalitis
Prevention: avoid mosquito bites