The Viruses

1. The Viruses I. Discovery of Virues A. MartinusBeijerinck 1. Considered the founder of virology 2. In 1898, he used filtration experiments to show tobacco mosaic disease is caused by an agent smaller than bacteria 3. Coined the word virus

2. B. Wendell Stanley 1. Isolated the tobacco mosaic virus (TMV) when he crystallized sap from tobacco leaves infected with tobacco mosaic disease (1935) 2. In 1939 TMV was observed with the electron microscope

3. II. Vectors A. Arthropod Vectors 1. Vectors play a key role in the dissemination of disease 2. Arthropods vectors can be mosquitoes, flies, sand flies, lice, fleas, ticks and mites 3. Many arthropod vectors are haematophagous, or blood feeders 4. A vector may not only be required for part of the parasite's developmental cycle, but also transmits the parasite directly to the host

4. Arthropod vectors Mosquito Tick Fly Kissing bug Lice Flea

5. III. General Characteristics of Viruses A. Are Viruses a Form of Life? 1. Nonliving characteristics viruses lack: a. plasma membrane b. cell wall c. cytoplasm d. organelles e. respiration f. binary fission g. food getting h. locomotion

6. 2. Living characteristics a. Reproduce within a living host cell

7. B. The Virus Mutation Rate is Extraordinarily High 1. Many viruses, in particular RNA viruses , have short generation times and relatively high mutation rates (on the order of one point mutation or more per genome per round of replication for RNA viruses) 2. This elevated mutation rate allows viruses to quickly adapt to changes in their host environment 3. Since viruses have such high mutation and reproductive rates, they can adapt to changing environments quite well

8. C. Nucleic Acids of Viruses 1. Viruses have either DNA or RNA as their genetic material, but never both -may be single or double stranded -may be linear or circular -may exist as a single piece of genetic material or multi-segmented pieces D. Capsids 1. Composed of proteins called capsomeres -capsomers may be composed of a single type of proteinor several types -the arrangement of capsomers is characteristic of a particular type of virus -they account for most of the mass of the virus -they determine the antigenicity of the virus

9. E. Envelopes 1. Some capsids are surrounded by an envelope a. the envelope is composed of lipids, proteins and carbohydrates b. the envelope is derived from • host cell membranes (can evade host defense mechanism) and/or • may contain some proteins synthesized from virus genes and/or • may contain some material derived from normal host cell components c. spikes of the envelope are composed of carbohydrate and proteins d. spikes are used for attachment to host cellsand are used to identify viruses

10. F. Types of Viruses 1. Polyhedral Viruses a. capsids forming multiple (many) sides b. icosahedron is a regular polyhedron with 20 triangular faces and 12 corners 2. Helical Viruses a. their nucleic acids are surrounded by a capsid which form long hollow rods

11. 3. Enveloped helical viruses 4. Enveloped polyhedral viruses 5. Complex viruses

12. Viruses must be grown in living animals or in embryonated eggs

13. IV. Bacterial Viruses- The Bacteriophages A. Bacteriophage Virus Structure

14. B. The Lytic Cycle

15. Bacterial chromosome Bacterial cell wall Capsid DNA Capsid Sheath Tail fiber Tail 1 Attachment:Phage attaches to host cell. Base plate Pin Cell wall Plasma membrane 2 Penetration:Phage pentrates host cell and injects its DNA. Sheath contracted Tail core 3 Biosynthesis

16. Tail DNA 4 Maturation:Viral components are assembled into virions. Capsid 5 Release:Host cell lyses and new virions are released. Tail fibers

17. Virual plaques- areas on a Petri plate where bacteria have been killed by viruses

18. C. Viral Reproduction in Bacteria

19. D. The Lysogenic Cycle

20. E. Specialized Transduction gal gene Prophage Bacterial DNA 1 Prophage exists in galactose-using host (containing the gal gene) Galactose-positive donor cell gal gene 2 Phage genome excises, carrying with it the adjacent gal gene from the host gal gene 3 Phage matures and cell lyses, releasing phage carrying gal gene Galactose-negative recipient cell 4 Phage infects a cell that cannot utilize galactose (lacking gal gene) 5 Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA 6 Lysogenic cell can now metabolize galactose

21. V. Human Viruses A. Mode of Attack 1. Attachment to a host cell and endocytosis 2. Penetration 3. Uncoating to expose the genetic material 4. Replication of viral components using host-cell machinery 5. Assembly of viral components into complete viral particles 6. Release of viral particles to infect new host cells. . Figure 13.14

22. Budding viruses

23. C. Viral Infections 1. Acute infections are characterized by the short period of time between initial infection and elimination by the host- ex. common flu 2. Latent infections invade host cells and remain dormant over a long period of time, producing no symptoms- herpes simplex virus (cold sores) 3. Persistent infections are considered chronic infections that occurs over a long period of time, often with fatal consequences- HIV/AIDS, cervical cancer, liver cancer

24. VI. Human DNA Viruses A. Human Papillomavirus (HPV) -Polyhedral virus that infects the skin and mucous membranes -The majority of the nearly 200 known types of HPV cause no symptoms in most cases -HPV can cause warts and cancer 1. Skin warts a. some HPV infections cause warts which are noncancerous skin growths b. common warts are warts on the hands and feet and more rarely on elbows or knees c. have a characteristic cauliflower morphology d. planter warts are found on the soles of the feet that grow inward

27. 2. HPV and Cancer a. around 500,000 new cancers are attributable to HPV (worldwide) b. about a dozen HPV types are called "high-risk" types because they can lead to cervical, anal, vulvar, vaginal and penile, mouth and throat cancers c. most common sexually transmitted infection d. 40 HPV types infect the genital areas of both males and females e. most people who become infected with HPV do not know they have it

28. 3. Multiplication of Papovaviruses- DNA Virus (Papilloma viruses ) Papovavirus 1 Virion attaches to host cell 7 Virions are released Host cell DNA Capsid 2 DNA Virion penetrates cell and its DNA is uncoated Cytoplasm 6 Virions mature Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 3 Early transcription and translation; enzymes are synthesized 4 Late transcription; DNA is replicated

29. B. Adenoviruses 1. Nonenveloped polyhedral viruses 2. 53 types in humans 3. Most common cause of illness of the respiratory system- common cold, pneumonia, croup, and bronchitis 4. Can cause tonsillitis, stomach flu, conjunctivitis and gastroenteritis

31. C. Orthopoxvirus 1. Smallpox is an infectious disease unique to humans 2. Smallpox is caused by two virus variants, Variola major and Variola minor 3. V. major produces a more serious disease and has an overall mortality rate of 30–35% 4. V. minor causes a milder form of disease that kills about 1% of its victims 5. Smallpox localizes in small blood vessels of the skin and in the mouth 6. During the 20th century, it is estimated that smallpox was responsible for 300–500 million deaths and has killed more people throughout history than any other infectious disease 7. After successful vaccination campaigns throughout the 19th and 20th centuries, smallpox was eradicated from natural existence as of December 1979 through a global vaccination effort administered by the World Health Organization (WHO)

32. 8. Smallpox is the only human infectious disease to have been eradicated 9. It is the ultimate weapon of mass destruction 10. Currently, the only official stores of Variola are in freezers of two research sites: CDC (Atlanta) VECTOR (Russia)

34. 2. The smallpox vaccine was the first successful vaccine that was developed by Edward Jenner in 1796

35. D. Herpes related virus -enveloped viruses 1. Chicken pox is a highly contagious illness caused by varicella zoster virus (VZV) -starts with a skin rash mainly on the body and head rather than at the periphery and becomes itchy

36. 2. Shingles a. the initial infection with varicella causes the acute (short-lived) illness chickenpox which generally occurs in children and young people b. varicella can become latent in the nerve cell bodies without causing any symptoms c. years or decades after a chickenpox infection, the virus may break out of nerve cell bodies and travel down nerve axons to cause viral infection of the skin in the region of the nerve and cause shingles

37. 3. Herpes simplex (HSV) a. HSV is never removed from the body by the immune system b. following a primary infection, the virus enters the nerves at the site of primary infection, migrates to the cell body of the neuron, and becomes latent in the ganglion c. Oral herpes are sometimes called cold sores or fever blisters that infect the face and lips.

38. Genital herpes

39. -Burkitt’s lymphoma-cancer of the lymphatic system - Kaposi's sarcoma

40. VII. RNA Viruses RNA A. Virus Reproduction

41. B. Orthomyxoviruses -enveloped virus -10 genes on 8 single strands of RNA molecules - bird and pig share virus; pig and human share virus -pigs provides a “mixing pot” able to be infected by the avian virus, thus allowing passage to humans -glycoprotein spikes of two types, H and N, are capable of “mix and match” causing antigenic shift -16 H types and 9 N types -H5 stands for the fifth of several known types of the protein hemagglutinin -N1 stands for the first of several known types of the protein neuraminidase

43. Spanish Flu Pandemic -it is thought to be one of the most deadly pandemics in world history -The Spanish flu was an unusually severe and deadly strain of avian influenza that killed some 50 to 100 million people worldwide over about a year in 1918 and 1919. -The 1918 flu caused an unusual number of deaths, possibly due to it causing a cytokine storm the body -The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lungs -This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ.

44. Influenza A Pandemics * Spanish flu (H1N1) pandemic- 1918 -deadly strain of avian influenza that killed an estimated 50 million to 100 million people -thought to be one of the most deadly pandemics in human history *Asian flu (H2N2)pandemic- 1957 -1.5 million deaths * Hong Kong flu (H3N2) pandemic- 1968 -1 million deaths * Avian flu (H5N1) 2007-2010 (human flu?) -antigenic shift could make this a deadly human virus with a mortality rate of 30-40% *Swine flu (H1N1) 2009-2010 -18,000 deaths

46. Influenza virus B 1. This genus has one species, influenza B virus 2. Influenza B almost exclusively infects humansand is less common than influenza A 3. mutates at a rate 2–3 times slower than type Aand consequently is less genetically diverse Influenza virus C 1. This genus has one species, influenza C virus. 2. Infects humans, dogs and pigs, sometimes causing both severe illness and local epidemics. However, influenza C is less common than the other types and usually only causes mild disease in children

47. C. Hepatitis C virus a. enveloped b. causes liver damage- hepatitis, cirrhosis of the liver, and liver cancer

48. D. Poliovirus -nonenveloped virus -causes polio -pandemic occurred during the 1950’s -eliminated in North and South America

49. Poliomyelitis immunization days

50. E. Rhinovirus -polyhedral -Rhinoviruses are the most common viral infective agents in humans, and a causative agent of the common cold -there are 99 recognized types of rhinoviruses that differ based on their varying surface proteins.