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Viruses

Explore the characteristics, sizes, and infection mechanisms of viruses, viroids, and prions. Learn about lytic and lysogenic cycles, viral infections, and how RNA viruses work. Understand the importance of vaccines in preventing viral diseases.

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Viruses

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  1. Viruses

  2. Are Viruses Living Things? Characteristics of Living things are… • Made of cells • Can reproduce • Based on a universal genetic code • Grow and develop • Obtain and use materials and energy • Respond to the environment • Maintain homeostasis • As a group, change over time * *

  3. Viral Characteristics • NON-LIVING • REPRODUCE ONLY WITHIN A HOST CELL by hijacking the cells’ machinery • NAMED FOR DISEASE THEY CAUSE OR PLACE • THEY INFECT

  4. Viruses are named for • The cells they attack • The disease they cause

  5. KEY CONCEPTInfections can be caused in several ways.

  6. Name tells you this virus infects bacteria

  7. Name tells you this virus causes influenza

  8. Viruses, bacteria, viroids, and prions can all cause infection. • Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells10,000-100,000 nm viroids5-150 nm viruses50-200 nm prokaryotics cells200-10,000 nm prion2-10 nm

  9. capsid DNA tail sheath tail fiber • Bacteriophages infect bacteria.

  10. Viral Size Viruses are very small. If an average virus were the size of an average person, a bacterial cell would be the size of a dinosaur over ten stories tall. Click on the picture for virus size activity

  11. A virus is made of DNA or RNA and a protein coat. • non-living pathogen • can infect many organisms • A viroid is made only of single-stranded RNA. • causes disease in plants • passed through seeds or pollen

  12. causes misfolding of other proteins • results in diseases of the brain • A prion is made only of proteins.

  13. KEY CONCEPT Viruses exist in a variety of shapes and sizes.

  14. How viruses enter our cells • The virus has an antigen that mimics a body cell • The antigen will fit in a cells receptor site • The cell allows the virus to enter the cell • A virus is very specific as to what type of cell it infects

  15. Which type of cell will be infected by the virus shown below?

  16. capsid surfaceproteins nucleic acid nucleic acid capsid Surface proteins lipidenvelope capsid nucleic acid surfaceproteins lipid envelope Viruses differ in shape and in ways of entering host cells. • Viruses have a simple structure. • genetic material (DNA or RNA) • capsid, a protein shell • maybe a lipid envelope, a protective outer coat enveloped(influenza) helical(rabies) polyhedral(foot-and-mouth disease)

  17. colored SEM; magnifications: large photo 25,000; inset 38,000x • bacteriophages pierce host cells • Viruses enter cells in various ways.

  18. Viruses enter cells in various ways. • viruses of eukaryotes also fuse with membrane

  19. How do viruses infect cells? • Once a virus enters a host cell, two different processes can occur: • Lysogenic cycle • Lytic cycle

  20. host bacterium The bacterophage attachesand injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells. The viral DNA forms a circle. The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages. The virus may enter the lysogenic cycle, in which the host cell is not destroyed. Viruses cause two types of infections. • A lytic infection causes the host cell to burst.

  21. Lytic Cycle • viral DNA is injected into the host cell • host cell begins to make mRNA from the viral DNA • viral proteins shut down the host cell’s regular functions • cell is used to make thousands of viruses (DNA and protein coats) • host cell bursts (lyses) and releases viruses to infect other cells

  22. Lytic Cycle • When a Lytic Virus infects a cell an immune response will immediately be triggered. • Examples: • The Cold, The Flu

  23. The prophage may leave the host’s DNA and enter the lytic cycle. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. • A lysogenic infection does no immediate harm.

  24. Lysogenic Cycle • viral DNA is injected into the host cell • DNA is integrated into the host DNA • host cell divides with the viral DNA as a part of it • eventually the viral DNA can be triggered to separate from the host cell DNA and pick up with the lytic cycle at step 2.

  25. Viruses cause many infectious diseases • There are many examples of viral infections. • common cold

  26. Viruses cause many infectious diseases • influenza • There are many examples of viral infections. • common cold

  27. How do RNA viruses work? • RNA viruses do not have built in proofreading, so they mutate and evolve quickly (like the flu). • A special kind of RNA virus, called a retrovirus, can cause DNA to be made from their RNA. • Certain cancers, and AIDS are caused by retroviruses.

  28. KEY CONCEPT Some viral diseases can be prevented with vaccines.

  29. Vaccines are made from weakened pathogens. • A vaccine stimulates the body’s own immune response. • Vaccines prepare the immune system for a future attack. • Vaccines are the only way to control the spread of viral disease.

  30. Fighting Disease • Vaccine • Weakened or dead version of a pathogen to trigger an immune response • Edward Jenner

  31. Viral Diseases

  32. Common Cold • Causes: • 200+ viruses can cause it, including rhinoviruses • No evidence for weather causing a cold • Symptoms: • Runny nose, sore throat, headache, cough • Treatment: • Antihistamines, decongestants & glycerin based cough suppressants • NSAIDS (ibuprofen) • Transmission: • Inhaling drops of mucus full of rhinovirus • Touching contaminated surfaces • Wash your hands!

  33. Influenza “the flu” • Cause: influenza (Types A,B & C) • Symptoms: • Fever, headache, fatigue, body aches, congestion • Treatment: • CDC currently recommends NOT taking medications for flu due to growing virus resistance. • Transmission: • Inhaling drops of mucus full of influenza virus • Touching contaminated surfaces • Status: • Vaccines present, BUT it changes yearly (RNA virus) • Threat of flu pandemics worldwide

  34. Smallpox • Cause: Variola • Symptoms: • High fever, body aches, small raised bumps all over body • Treatment: • no proven treatment for smallpox • Most recover, 30% mortality • Transmission: • inhaling droplets of affected saliva • face-to-face contact with an infected person • Status: • Vaccine present • Can be fatal • Eradicated worldwide, last naturally occurring in 1977

  35. Herpes Simplex I Cause: (HSV-1) Herpes Simplex Virus Type 1 Symptoms: Cold sores around mouth Treatment: Topical medication to reduce outbreaks Antiviral medication to reduce number of outbreaks Transmission: Kissing, eating/drinking after one another Status: No vaccine, no cure! HSV-1

  36. Cause: (HSV-2) Herpes Simplex Virus Type 2 Symptoms: Pain, itching, blisters on genitals, anus and thighs Treatment: medication to reduce symptoms and reduce number of outbreaks Transmission: Sexually transmitted, may not be showing signs, oral or vaginal sex Status: No vaccination, no cure! 1 out of 5 adolescents and adults have had HSV-2 in the US! Herpes Simplex II Perianal HSV-2

  37. Human Papillomavirus (HPV-warts) Cause: >100 strains of Human Papillomavirus (HPV) Symptoms: Raised or flat, single or multiple swellings on any genital surface, male or female, can appear cauliflower-like Can cause cervical cancer in women No visible signs may occur Treatment: Topical creams are available, doctors may freeze or burn them off May remove warts but virus is still present in the body and warts may return Transmission: Very contagious sexual contact with infected partner, may not be showing signs Status: 6.2 million new cases a year in U.S. No cure! Tests available for presence in women Gardasil- new vaccine that prevents the 4 highest risk strains of HPV

  38. Hepatitis B • Cause: Hepatitis B virus (HBV) • Symptoms: • Cirrhosis (scarring of the liver), liver cancer, liver failure, death • May not look sick • Treatment: • Interferon- slows the growth of HBV • Transmission: • Any sexual contact • Blood contact (needles, razors, etc.) • Status: • Vaccine is available • 1.25 million American live with chronic hepatitis B Female Cambodian patient with a distended abdomen due to a hepatoma resulting from chronic hepatitis B infection Juandice

  39. Rabies • Cause: rabies virus • Symptoms: • Fever, headache, paralysis, hydrophobia, hallucinations, foaming at the mouth, ultimately death • Treatment: no successful treatment • Transmission: • bite from an infected mammal (carnivores and bats) • Status: • Cases have reduced in domestic animals greatly • Vaccine is available, only given to people at high risk of infection

  40. HIV (Human Immunodeficiency Virus) • The HIV virus infects cells of the immune system called Helper T cells. • Normally Helper T cells activate cells that produce antibodies and cells that destroy cells infected by a pathogen. • When a Helper T cell is infected by the HIV virus, the immune system cannot fight off infections from pathogens such as bacteria and other viruses.

  41. HIV (Human Immunodeficiency Virus) • HIV can cause AIDS (Acquired Immunodeficiency Syndrome) when enough Helper T cells are infected so the immune system does not work properly. • People with HIV infections can get sick easily because their immune system does not work properly. People with AIDS do not die from the HIV virus, but from these other infections.

  42. HIV (Human Immunodeficiency Virus) Cause: Human Immunodeficiency Virus Symptoms: Fever, headache, tiredness, enlarged lymph nodes AIDS (Acquired Immunodeficiency Syndrome) weight loss, fatigue, memory loss Destroys Helper T cells (part of immune system) body cannot fight off illnesses caused by bacteria, other viruses, fungi, or parasites. Ultimately leads to death

  43. HIV (continued) Treatment: Reverse Transcriptase (RT) inhibitors & Protease Inhibitors- stops the virus from making copies of itself Transmission: sexually (orally, vaginally) Blood (needles, or through mucus membranes) Breast milk mother to child NOT from kissing, touching, insects bites Status: No vaccine, several medicines to prevent spread in body Worldwide: In 2004, 40 million people living with HIV/AIDS, 5 million newly infected, and 3.1 million deaths Prevention: Abstinence, Safe sex (Condoms!), avoidance or risky behaviors associated with sex and drug use

  44. Ebola Hemorrhagic Fever Electron micrograph of ebola virus • Cause: • 1 of 4 Ebola viruses • Symptoms: • Fever, headache, muscle/joint pain, red eyes, skin rash • Diarrhea, vomiting, rash, internal and external bleeding • Treatment: • No standard treatment • Some patients recover but majority die, usually because the lack of immune response • Transmission: • Contaminated body fluids: Blood, mucus, semen, syringes • Air transmission in monkey Ebola-Reston virus only • Status: • Only identified in 1976 with few devastating outbreaks • RNA virus

  45. Measles Rubella Other viral diseases • Polio • Shingles/ chicken pox • Hanta • SARS • Stomach virus (viral gastroenteritis) • Viral meningitis • Rubella, Measles, mumps Polio

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