Note Sheet 16 - Viruses

1. Note Sheet 16 - Viruses Swine (H1N1) Flu Viruses

2. What is a virus? • Virus – a particle made of a nucleic acid (DNA or RNA) surrounded by protein coat • Capsid – the outer coat of protein that covers a virus • Viruses are extremely small – Millions of them could fit into one single cell • Viruses are grouped by the type of organisms they infect – There are 3 main types of viruses: plant viruses, animal viruses, and bacterial viruses

3. Virus Types

4. Viruses are small • http://learn.genetics.utah.edu/content/begin/cells/scale/

5. Some viruses cause disease • Many human diseases are caused by viruses • Common cold • Flu • AIDS • Rabies

6. What is the flu? • Influenza (the flu) is a contagious respiratory illness caused by influenza viruses • It can cause mild to severe illness, and at times can lead to death • Each year in the United States on average, 5% to 20% of the population gets the flu; on average, more than 200,000 people are hospitalized from flu-related complications, and; about 36,000 people die from flu-related causes • There are many different types of flu virus, or “strains” that circulate from year to year and make people sick

7. What is “swine” or “H1N1” flu? • Swine flu is a new strain of the flu virus that was first identified passing from human to human earlier this year • Because this particular virus has never circulated in human populations before, nobody has immunity • Many more people than usual have become, and will become infected with this particular strain of the virus

8. Percentage of Visits for Influenza-like Illness (ILI) Reported by the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), National Summary 2008-2009 and Previous Two Seasons (Week ending 11-14-09)

9. Swine Flu Virus

10. Swine Flu Virus • Blue and Red “spikes” represent surface proteins • Blue are hemagglutinin (HA) proteins • Red are neuraminidase (NA) proteins

11. Flu Virus Names • There are 16 types of HA protein and 9 types of NA protein • A flu virus has only one type of HA and one type of NA, so that is how they are named • Swine flu is grouped as an “H1N1” virus because it has type 1 HA protein and type 1 NA protein

12. Viruses do NOT have all the characteristics of life Viruses are NOT made of cells and do not have cell parts Viruses do NOT take in or use energy Viruses CANNOT reproduce by themselves Although there is some argument, most biologists do not consider viruses to be living Is a virus a living thing?

13. Where do viruses come from? • Viruses enter living cells and use the cell parts of the infected cell to build more viruses • Host cell – a cell that has been infected by a virus

14. What happens when a virus infects a cell? • Lytic Cycle – process where a virus enters a cell, makes copies of itself, and causes the cell to burst, releasing the new viruses

15. What happens when a virus infects a cell? • Lytic Cycle – process where a virus enters a cell, makes copies of itself, and causes the cell to burst, releasing the new viruses

16. What happens when a virus infects a cell? • Lytic Cycle – process where a virus enters a cell, makes copies of itself, and causes the cell to burst, releasing the new viruses

17. What happens when a virus infects a cell? • Lytic Cycle – process where a virus enters a cell, makes copies of itself, and causes the cell to burst, releasing the new viruses

18. Flu Attack! How A Virus Invades Your Body • http://www.xvivo.net/zirus-antivirotics/

19. What happens when a virus infects a cell? • Lysogenic Cycle – process where the virus injects its DNA into the DNA of the host cell which is then replicated along with the host cell’s DNA • Eventually, the virus DNA will begin making more viruses (lytic cycle) • Viruses either make more viruses immediately (lytic cycle) or “hide out” for a while (lysogenic cycle)

20. The Common Cold – What is it? • The common cold is a group of symptoms in the upper respiratory tract caused by a large number of different viruses • Although more than 200 viruses can cause the common cold, the perpetrator is usually the rhinovirus, which is to blame for causing 10% to 40% of colds • Also, the coronaviruses cause about 20% of colds

21. Corona Virus

22. Rabies Virus

23. HIV (Human Immunodeficiency Virus)

25. Viruses attack and destroy specific types of cells, causing the symptoms of particular diseases (flu, common cold, AIDS, rabies) Vaccine – a weakened or killed virus that is injected into the body so the immune system can recognize the virus and destroy it Vaccines only work if they are given before an infection – once a viral disease is contracted, it is often too late to control it How do we defend against viruses?

27. Vaccine Success Story - Smallpox • Smallpox is a highly infectious, devastating, and disfiguring disease that is caused by variola virus • Smallpox is characterized by numerous pustules containing infectious virus all over the body • The fatality rate is more than one quarter of infected patients infected by the most serious form caused by Variola major

28. Vaccine Success Story - Smallpox • The disease killed an estimated 400,000 Europeans each year during the 18th century • Of all those infected, 20–60% — and over 80% of infected children — died from the disease • In the United States, from 1843 to 1855 first Massachusetts, and then other states required smallpox vaccination • By 1897, smallpox had largely been eliminated from the United States • In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year • After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in December 1979 • The last cases of smallpox in the world occurred in an outbreak of two cases (one of which was fatal) in Birmingham, England in 1978

29. Vaccine Success Story - Polio • Polio is a viral disease, usually affecting children and young adults, caused by any of three polioviruses • Polio virus causes inflammation of the motor neurons of the brain stem and spinal cord • Symptoms include motor paralysis, followed by muscular atrophy and often permanent deformities • Polio was one of the most dreaded childhood diseases of the 20th century • Polio epidemics have crippled thousands of people, mostly young children; the disease has caused paralysis and death for much of human history

30. By 1910, much of the world experienced a dramatic increase in polio cases and frequent epidemics became regular events, primarily in cities during the summer months These epidemics left thousands of children and adults paralyzed The polio vaccines developed by Jonas Salk in 1952 and Albert Sabin in 1962 are credited with reducing the global number of polio cases per year from many hundreds of thousands to around a thousand Vaccine Success Story - Polio

31. Why don’t we have vaccines for all viral diseases? • There are many problems inherent in developing a good protective anti-viral vaccine • Different types of virus may cause similar diseases -- e.g. the common cold. As a result, a single vaccine will not be possible against such a disease • Viruses can change as they circulate (mutation) • Large animal reservoirs. If these occur, re-infection after elimination from the human population may occur.