1. Donna Howell Medical Microbiology Gaffney High School
Coming soon to a body near you -
He He He!
The Viruses Unit 3
Donna Howell
Medical Microbiology
Gaffney High School

2. History
In 1892, Dmitri Iwanowski studied the tobacco mosaic virus. He found out that this unknown agent could pass through a filter, unlike bacteria.
In 1930’s, Wendell Stanley found out that this unknown agent could crystallize, which means it is a chemical.
In 1933, electron microscope was invented, and could see viruses by 1941.

3. What is a Virus?
Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.

4. How Are Viruses Classified?
DNA or RNA – that is the question!
Viruses are classifed according to what type of nucleic acid core they contain: either RNA or DNA.

5. Further Classification
Viruses can be further classified based on what part of the body is affected:
Category
Tissue Affected
Example Diseases
Dermotropic
Skin and subcutaneous tissue
Chicken pox, shingles, measles, mumps, smallpox, rubella, herpes simplex
Neurotropic
Brain and central nervous system tissue
Rabies, West Nile virus, polio
Viscerotropic
Internal organs
Yellow fever, AIDS, Hepatitis A and B, Mono, Dengue fever
Pneumotropic
Lungs and other respiratory structures
Influenza, common cold

6. Size Of Viruses
Viruses are among the smallest known infectious particles. They come in many sizes:

7. Did You Know?
There is a connection between herpes and psychosis due to inflammation of the brain!

8. Shapes Of Viruses
Viruses also come in many different shapes:

9. Components Of Viruses Capsid – the outer protein coat
Capsomere – protein units that make up the capsid
Genome – DNA or RNA
Envelope – an enclosing structure similar to cell membrane
Spikes – projections on outside of virus that allow it to attach to host cell

10. Viral Replication
Viruses can replicate (reproduce) in one of two ways:
Lytic cycle – this is where the virus replicates in the host cell, and causes host cell to “lyse”, or burst to release new viruses
Lysogenic cycle – this is where the virus incorporates its DNA into the host DNA as a prophage, and replicates as host DNA replicates.

11. Lytic Cycle There are 6 stages of this cycle:
Attachment – virus attaches to host
Penetration – virus enters host
Uncoating – capsid removed, nucleic acid released
Synthesis – parts for new viruses synthesized
Assembly – parts are assembled
Release – host cell lyses, new viruses released
Ex: Flu virus

12. Lysogenic Cycle
This is when the virus enters the host cell, but does not replicate immediately. Instead, it incorporates its genes into the host’s genes, and then one day will complete the lytic cycle. Ex: AIDS

13. Viral Identification
In many cases, when a virus infect a cell, it causes cell death or at least cell damage. The specific imprint that the virus leaves is called the cytopathic effect (CPE). By observing the effects under the microscope, scientists can sometimes identify the type of viral infection. Many viruses have a characteristic CPE.

14. How Are Viruses Cultured?
Touch my egg you die, buster!
Viruses can be cultured in one of 3 ways:
Inside a live animal
Inside a fertilized chicken egg
In a viral cell culture, which is a thin layer of cells in a petri dish with special nutrients

15. Did You Know?
Shake ya tailfeathers!
There is a link between in-utero exposure to flu and schizophrenia later in life!

16. Defenses Against Viruses
Go body go!
What are some defenses against viruses?
Body can produce antibodies, which attack and kill viruses.
Some drugs can be used, such as interferon or AZT
Can have a vaccine against a virus

17. Types of Vaccines I got your vaccine, baby!
There are 3 types of vaccines that we use for viruses:
Inactivated vaccine – those made from real inactivated virus. The genome is destroyed, but the capsid remains.
Attenuated vaccine – those made from “live” viruses, but in such a low dose that it does not usually cause disease.
Genetically-engineered vaccine – viral proteins are produced by yeast cells, so NO actual viruses used. Safest!

18. Viroids
Come on viroids!
An ultramicroscopic, single-stranded molecule of RNA without a protein coat.
Mostly infect plants
Cause stunted growth and abnormal development.

19. Prions
I’m a mad cow – get it?
Proteinaceous infectious particle (single piece of protein with no capsid)
Can survive heat, radiation, and chemicals that normally inactivate viruses.
Causes kuru and mad cow disease.

20. Get it – horoscope, cancer, crab????
Viruses and Cancer
Get it – horoscope, cancer, crab????
It is well known that certain viruses have cancer-causing abilities. Here are a few:
HPV virus – cervical cancer
Hepatitis B virus – liver cancer
HTLV virus – leukemia
Epstein-Barr virus – Burkitt’s lymphoma

21. HIV Virus (AIDS)

22. Human Papilloma Virus (Genital Warts)

23. Herpes Virus (Chicken Pox)
Chickens don’t have pox!

24. Filovirus – Ebola Hemorrhagic Fever

25. Rotavirus – The “Stomach Bug”

26. HBV – Hepatitis B

27. Orthomyxovirus – The “Flu”

28. Paramyxovirus (Measles)

29. Picornavirus (Polio)

30. Rhabdovirus (Rabies)

31. Science is cute and cuddly, boys!
The End!
Science is cute and cuddly, boys!