Viruses are non-living particles that can only reproduce inside host cells. They are much smaller than bacteria and come in various shapes. Viruses cause diseases like smallpox, influenza, and AIDS. They enter cells and use the cell's machinery to replicate themselves before destroying the cell. While viruses cannot live outside of a host, they have developed ways to spread between hosts, such as through respiratory droplets or animal vectors. The best ways to prevent viral spread are vaccination, good hygiene like handwashing, and avoiding contact with infected bodily fluids.

1. CHARACTERISTICS OF VIRUSES

2. Many common illnesses are caused by viruses. Viruses are easily killed by drugs such as antibiotics. Once you have contracted a specific virus, you will not get sick from this virus again because of the antibodies produced in your body. Many diseases caused by viruses can be avoided through vaccination. Viruses are very fragile and cannot live on surfaces outside fo the human body. Viruses have the ability to change themselves, or mutate, over time. Pre-Quiz (True or False)

3. 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.

4. Are Viruses Living or Non-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

5. What are Viruses? 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 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 Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants He discovered viruses were made of nucleic acid and protein

8. Smallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Deadly viruses are said to be virulent Smallpox has been eradicated in the world today

9. 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 inch 1000x smaller than bacteria Bacteria = much smaller than a human cell

10. Characteristics Non living structures Non-cellular Contain a protein coat called the capsid Have a nucleic acid core containing DNA or RNA (one or the other - not both) Capable of reproducing only when inside a HOST cell

11. Characteristics 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. Characteristics Outside of host cells, viruses are inactive Lack ribosomes and enzymes needed for metabolism Use the raw materials and enzymes of the host cell to be able to reproduce EBOLA VIRUS HIV VIRUS

13. Characteristics 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 leukemia Virus-free cells are rare MEASLES

14. 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: Helical Viruses

16. Polyhedral Viruses

17. Complex Viruses

18. Viral Taxonomy Family names end in - viridae Genus names end in - virus Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species Subspecies are designated by a number

19. Viral Taxonomy Examples Herpesviridae Herpesvirus Human herpes virus 1, HHV 2, HHV 3 Retroviridae Lentivirus Human Immunodeficiency Virus 1, HIV 2

20. RNA or DNA Virus Do or do NOT have an envelope Capsid shape HOST they infect Used for Virus Identification

21. Herpes Virus SIMPLEX I and II

22. Adenovirus COMMON COLD

23. Influenza Virus

24. Chickenpox Virus

25. Papillomavirus – Warts!

26. Bacteriophages

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

28. T-phages The most commonly studied T-phages are T4 and T7 They infect E. coli , an intestinal bacteria Six small spikes at the base of a contractile tail are used to attach to the host cell Inject viral DNA into cell

29. Retroviruses

30. Characteristics of Retroviruses Contain RNA, not DNA Family Retroviridae Contain enzyme called Reverse Transcriptase When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell Examples: HIV, the AIDS virus, Feline Leukemia Virus

31. Viroids Small, circular RNA molecules without a protein coat Infects plants Potato famine in Ireland

32. Prion Diseases Prions have no DNA or RNA Prions form insoluble deposits in the brain Causes neurons to rapidly degeneration. Mad cow disease (bovine spongiform encephalitis: BSE) is an example People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies

33. Viral 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 Cycle 1. Attachment to the cell 2. Penetration (injection) of viral DNA or RNA 3. Replication (Biosynthesis) of new viral proteins and nucleic acids 4. Assembly (Maturation) of the new viruses 5. Release of the new viruses into the environment (cell lyses)

35. Bacteriophage Replication Bacteriophage inject their nucleic acid They lyse (break open) the bacterial cell when replication is finished

36. INFECTION

37. Viral Latency Some viruses have the ability to become dormant inside the cell Called latent viruses They may remain inactive for long periods of time (years) Later, they activate to produce new viruses in response to some external signal HIV and Herpes viruses are examples

38. Lysogenic Cycle Phage DNA injected into host cell Viral DNA joins host DNA forming a prophage When an activation signal occurs, the phage DNA starts replicating Viral DNA (part of prophage) may stay inactive in host cell for long periods of time

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

40. Latency 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

41. 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

42. 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. Vaccines 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

44. 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 Treatments Interferon are naturally occurring proteins made by cells to fight viruses Genetic altering of viruses (attenuated viruses) Antiviral drugs (AZT) Protease inhibitors – prevent capsid formation copyright cmassengale

46. 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