1. Viruses

2. Discovery of Viruses What is a virus?
A nonliving particle made up of nucleic acid and a protein coat or a nucleic acid and a lipid-protein coat.

3. Discovery of Viruses
Late 1800’s researchers found that something smaller than bacteria could cause disease
1935 Wendell demonstrated that viruses were not cells

4. Characteristics of Viruses
Viruses are not living
They cannot:
Carry out metabolism or homeostasis
Do not grow or divide
Cannot reproduce outside their host cell

5. Viral Size and Structure
Viruses are some of the smallest particles that are able to cause disease
Shape is a result of its genome and the protein coat
Two main structures:
Capsid
Envelope

6. Viral Size and Structure
Capsid, or protein coat, is the only layer surrounding some viruses.
These capsids have different shapes depending on the virus
Envelope is a bilipid membrane that surrounds the capsid

7. Viral Size and Structure

8. Classification of Viruses
Viruses are classified by:
Whether they have RNA (Retrovirus) or DNA
Nature of their capsid and the presence/absence of an envelope

9. Viral Replication Two ways for DNA viruses:
DNA viruses can enter host cells and directly produce RNA
Insert into a host’s chromosome, where they are transcribed to RNA along with the host’s DNA

10. Viral Replication RNA Virus Replication:
The RNA genome of some RNA viruses can be directly translated to make viral proteins
RETROVIRUS use reverse transcriptase and RNA as a template to make DNA

11. Viral Replication (Lytic)
1) Viruses attach to the surface of the host cell
2) The virus injects its genetic material into the cell. The viruses genetic material takes over many of the cell’s functions.
3) The viruses genetic material instructs the cell to produce the virus’s proteins and genetic materials

12. Viral Replication
4) The proteins and genetic material assemble into new viruses that fill the cell
5) The cell bursts open, releasing new viruses. The viruses go on to infect more cells

13. Viral Replication
Bacteriophages
Viruses that infect bacteria

14. Lytic cycle

15. Lysogenic
In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell
The viral genetic information then replicates along with the host cell’s DNA
Remains inactive for a period of time
Viral DNA that is embedded in the host’s DNA is called a prophage

16. Viral Diseases
Vectors (hosts)
Humans
Animals
Insects
Plants
Bacteria

17. Human Viruses Vectors can transmit many viral diseases in humans like:
Common Cold
Flu
HIV
Hepatitis
Rabies
Chickenpox

18. Viral Diseases
Some viruses contain oncogenes, which are cancer causing agents.
Emerging viruses usually infect animals isolated in nature but can jump to humans when contact occurs in the environment

19. Prevention and Treatment
Vaccinations
A vaccine contains a harmless version of a virus, bacterium, or a toxin that causes an immune response when introduced to the body
Vector Control
Controlling insects and quarantining people have reduced the spread of diseases

20. Drug Therapy Antibiotics are ineffective against viral diseases
Viral drugs, such as acyclovir, block reproduction in viral replication.

21. Viroids and Prions Viroids
Short, circular, single-strands of RNA lacking a capsid that infect plant cells
Prions
Infectious particles that contain proteins but no nucleic acids
Cause Mad Cow disease and other degenerative brain diseases

22. Influenza Virus Caused by RNA virus Changes every year
Typically transmitted through the air or direct contact
Attacks the tissues in the lungs
Influenza of Pandemic 1918
Pandemic: disease that infects numerous people across continents

23. Influenza Virus

24. Common Cold RNA Virus Changes all the time
Most frequent infectious disease in humans
Infects the tissues in the lungs
Transmitted through direct contact or through the air

25. Polio DNA Virus Primarily transmitted by fecal-oral
Attacks tissue in the central nervous system

26. HIV Human Immunodeficiency Virus RNA Virus Routes of Transmission:
Transfer of bodily fluids
Transfer of blood
Attacks your immune system
Causes AIDS