Virus

CHARACTERISTICS OF VIRUSES

1. Many common illnesses are caused by viruses.

2. Viruses are easily killed by drugs such as antibiotics.

3. Once you have contracted a specific virus, you will not get sick from this virus again because of the antibodies produced in your body.

4. Many diseases caused by viruses can be avoided through vaccination.

5. Viruses are very fragile and cannot live on surfaces outside fo the human body.

6. Viruses have the ability to change themselves, or mutate, over time.

Pre-Quiz (True or False)

Pre-Quiz Continued

7. Viral illnesses cannot be transferred from animals to people.

8. The only way to transmit viruses is through close physical contact with an infected person.

9. Viruses can become resistant to drugs used to treat them.

10. One of the best ways to prevent the spread of viral diseases is frequent, thorough hand washing.

Are Viruses Living or Non-Are Viruses Living or Non-living?living?

Biologists consider viruses to be non-living because:– Are not cells– Do not use energy to grow or respond to their

surroundings– Cannot make food, take in food, or produce wastes– Viruses do not respond to stimuli in the environment

such as light, temperature, chemicals, sound, gravity, heat, water and pressure.

They can only multiply like other organisms but only inside a living cell

What are Viruses?What are Viruses?Definition-Definition-

Viruses are noncellular particles made up of genetic material and protein that can invade living cells.

Small, non-living, invades and reproduces inside a living cell

1 virus- can produce thousands of new viruses

6

Discovery of VirusesDiscovery of Viruses

Beijerinck (1897) coined the Latin name “virus” meaning poison

He studied filtered plant juices & found they caused healthy plants to become sick

7

Tobacco Mosaic VirusTobacco Mosaic Virus

Wendell Stanley (1935) crystallized sap from sick tobacco plants

He discovered viruses were made of nucleic acid and protein

8

SmallpoxSmallpox

Edward Jenner (1796) developed a smallpox vaccine using milder cowpox virusesDeadly viruses are said to be virulentSmallpox has been eradicated in the world today

How Big is a Virus?

Viruses are very small – smaller than the smallest cell.– They may vary in size from 20-400 nm.

Measured in nanometers (nm = one billionth of a meter)

one millionth of an inch1000x smaller than bacteriaBacteria = much smaller than a human cell

10

CharacteristicsCharacteristics

Non living structuresNon-cellularContain a protein coat called the capsidHave a nucleic acid core containing DNA

or RNA (one or the other - not both)Capable of reproducing only when inside

a HOST cell

11


Some viruses are enclosed in an protective envelope

Some viruses may have spikes to help attach to the host cell

Most viruses infect only SPECIFIC host cells

CAPSID

ENVELOPE

DNA

SPIKES

12


Outside of host cells, viruses are inactiveLack ribosomes and enzymes needed for metabolismUse the raw materials and enzymes of the host cell to be able to reproduce

EBOLA VIRUS

HIV VIRUS

13


Viruses cause many common illnesses diseases

Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola, the “flu,” chicken pox, measles, polio, and hepatitis

Some viruses may cause some cancers like leukemiaVirus-free cells are rare

MEASLES

What do Viruses look like?

Viruses are unusual and different from other things in nature.

Viruses come in a variety of shapes– Some are rod-shaped, round-shaped, tadpole-shaped, many-

sided, helical, cube-like and so on. Some may be helical shape like the Ebola virus Some may be polyhedral shapes like the influenza

virus Others have more complex shapes like

bacteriophages

THEY JUST DON’T LOOK LIKE OTHER THINGS!

15

Types of Viruses: Types of Viruses: Helical VirusesHelical Viruses

16

Polyhedral VirusesPolyhedral Viruses

17

Complex VirusesComplex Viruses

18

Viral TaxonomyViral Taxonomy

Family names end in -viridaeGenus names end in -virus Viral species: A group of viruses sharing

the same genetic information and ecological niche (host).

Common names are used for speciesSubspecies are designated by a number

19

Viral Taxonomy Viral Taxonomy ExamplesExamples

Herpesviridae Herpesvirus Human herpes virus 1, HHV 2, HHV 3

Retroviridae Lentivirus Human Immunodeficiency Virus 1, HIV 2

20

RNA or DNA VirusDo or do NOT have an envelopeCapsid shapeHOST they infect

Used for Virus Used for Virus IdentificationIdentification

21

Herpes VirusHerpes Virus

SIMPLEX I and II

22

AdenovirusAdenovirus

COMMON COLD

23

Influenza VirusInfluenza Virus

24

Chickenpox VirusChickenpox Virus

25

Papillomavirus – Papillomavirus – Warts!Warts!

26

Bacteriophages

27

PhagesPhages

Viruses that attack bacteria are called bacteriophage or just phageT-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

28

T-phagesT-phages

The most commonly studied T-phages are T4 and T7They infect E. coli , an intestinal bacteriaSix small spikes at the base of a contractile tail are used to attach to the host cell Inject viral DNA into cell

29

RetrovirusesRetroviruses

30

Characteristics of Characteristics of RetrovirusesRetroviruses

Contain RNA, not DNAFamily RetroviridaeContain enzyme called Reverse TranscriptaseWhen a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cellExamples: HIV, the AIDS virus, Feline Leukemia Virus

31

ViroidsViroids

Small, circular RNA molecules without a protein coat

Infects plants

Potato famine in Ireland

32

Prion DiseasesPrion DiseasesPrions have no DNA or Prions have no DNA or RNARNA

Prions form insoluble Prions form insoluble deposits in the braindeposits in the brainCauses neurons to Causes neurons to rapidly degeneration.rapidly degeneration.Mad cow disease (bovine Mad cow disease (bovine spongiform encephalitis: spongiform encephalitis: BSE) is an exampleBSE) is an examplePeople in New Guinea People in New Guinea used to suffer from kuru, used to suffer from kuru, which they got from which they got from eating the brains of their eating the brains of their enemiesenemies

33

Viral AttackViral Attack

Viruses are very specific as to which species they attack

HOST specific A vector is a host that transfers viruses to another

organism Example – West Nile Virus is spread through

mosquitoes Humans rarely share viral diseases with other

animals Eukaryotic viruses usually have protective

envelopes made from the host cell membrane

34

5 Steps of Lytic 5 Steps of Lytic CycleCycle

1. Attachment to the cell2. Penetration (injection) of viral DNA

or RNA3. Replication (Biosynthesis) of new

viral proteins and nucleic acids4. Assembly (Maturation) of the new

viruses 5. Release of the new viruses into

the environment (cell lyses)

35

Bacteriophage Bacteriophage ReplicationReplication

Bacteriophage inject their nucleic acidThey lyse (break open) the bacterial cell when replication is finished

INFECTION

37

Viral LatencyViral Latency

Some viruses have the ability to become dormant inside the cellCalled latent virusesThey may remain inactive for long periods of time (years)Later, they activate to produce new viruses in response to some external signalHIV and Herpes viruses are examples

38

Lysogenic Lysogenic CycleCycle

Phage DNA injected into host cell Viral DNA joins host DNA forming a prophageWhen an activation signal occurs, the phage DNA starts replicatingViral DNA (part of prophage) may stay inactive in host cell for long periods of time

39

Latency in Latency in EukaryotesEukaryotes

Some eukaryotic viruses remain dormant for many years in the nervous system tissues Chickenpox (caused by the virus Varicella zoster) is a childhood infectionIt can reappear later in life as shingles, a painful itching rash limited to small areas of the body

SHINGLES

40

Latency in EukaryotesLatency in Eukaryotes

Herpes viruses also become latent in the nervous system

A herpes infection lasts for a person’s lifetime

Genital herpes (Herpes Simplex 2)

Cold sores or fever blisters (Herpes Simplex1)

SKIN TO SKIN CONTACT

PASSED AT BIRTH TO BABY

HOST SPECIFICITY

All kingdoms can be infected by viruses Viruses that infect organisms of one kingdom are

not able to infect organisms of another kingdom Viruses can infect species of organisms that are

closely related or not closely related (some viral diseases can be passed from different species)

Viruses can even be species specific (only passed within the same species)

Spread is specific to the type of virus

-Carrier organisms, the air, direct transfer of body fluids

-Surfaces on which body fluids have dried

PARASITISM

Viruses are parasites.– A parasite is an organism that depends upon

another living organism for its existence in such a way that it harms that organism.

– Viruses must infect living cells in order to carry out their functions of growth and reproduction.

– Viruses depend upon their hosts for respiration, nutrition and all the other functions that occur in living things.

43

VaccinesVaccines

An attenuated virus is a weakened, less vigorous virus

“Attenuate" refers to procedures that weaken an agent of disease (heating)

A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus

Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

Viral illness

Treatment of viral disease include vaccination, vector control, and drug therapy

Drug therapy does NOT work very well Vaccination and vector control are the most

successful way to beat viruses Vaccination works because once you are

exposed to and overcome a virus your immune system creates antibodies that will immediately attack the virus if it shows up again

Hand-washing is effective against bacterial diseases and viral diseases

45

Other Viral TreatmentsOther Viral Treatments

Interferon are naturally occurring proteins made by cells to fight virusesGenetic altering of viruses (attenuated viruses)Antiviral drugs (AZT)Protease inhibitors – prevent capsid formation

copyright cmassengale

Reducing the Risk

Cover mouth/nose when you sneeze of cough

Wash hands frequently Avoid contact with the body fluids

Not foolproof but reduces the risks

Education

Virus