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Program PGMIPABIFakultas Keguruan dan Ilmu PendidikanUniversitas Syiah KualaAn Introduction to the Viruses
History (1)• For many years, the cause of viral infections such as  smallpox and polio was unknown, even though it was  cl...
History (2)• The first substantial revelations about the unique  characteristics of viruses occurred in the 1890s.  • Firs...
History (3)• Over the succeeding decades, a remarkable picture of  the physical, chemical, and biological nature of viruse...
The Position of Viruses in the BiologicalSpectrum• Viruses are a unique group of biological entities known  to infect ever...
Properties of Viruses   Program PGMIPABI-FKIP Unsyiah
General Structure of Viruses• As a group, viruses represent the smallest  infectious agents.• Their size places them in th...
The Size of VirusesSize comparison of viruses with a eukaryotic cell (yeast) and bacteria. Viruses range from largest (1) ...
Viral Components: Capsids, Nucleic Acids,and Envelopes (1)• The general plan of virus organization is the  utmost in simpl...
Viral Components: Capsids, Nucleic Acids,and Envelopes (2)               Program PGMIPABI-FKIP Unsyiah
Capsids (1)• All viruses have capsids - protein coats that  enclose and protect their nucleic acid.• Each capsid is constr...
Capsids (2)Generalized structure of viruses. (a) The simplest virus is a naked virus (nucleocapsid) consisting of a geomet...
Capsids (3)• Two structural types:  • helical - continuous helix of capsomers forming a    cylindrical nucleocapsid    •  ...
Helical capsidsTypical variations of viruses with helical nucleocapsids. Naked helical virus (tobacco mosaic virus):(a) a ...
Icosahedral viruses (1)              Program PGMIPABI-FKIP Unsyiah
Icosahedral viruses (2)Two types of icosahedral viruses, highly magnified. (a) Upper view: A negative stain of rotaviruses...
Viral envelope• When enveloped viruses (mostly animal) are released from the  host cell, they take with them a bit of its ...
Functions of Capsid/Envelope• The outermost covering of a virus is  indispensable to viral function  • it protects the nuc...
Complex viruses: atypical viruses (1)• Two special groups of viruses, termed complex viruses  are more intricate in struct...
Complex viruses: atypical viruses (2)Detailed structure of complex viruses. (a) Section through the vaccinia virus, a poxv...
Basic types of viral morphologyA. Complex viruses: (1) poxvirus, a large DNA virus (2) flexible-tailed bacteriophageB. Env...
Nucleic acids (1)• Viral genome – either DNA or RNA but never  both• Carries genes necessary to invade host cell and  redi...
Nucleic acids (2)• DNA viruses  • usually double stranded (ds) but may be single stranded    (ss)  • circular or linear• R...
Other Substances in the VirusParticle• In addition to the protein of the capsid, the proteins and lipids of  envelopes, an...
How Viruses Are Classified andNamed (1)• Classified based on structures, size, nucleic acids,  host species, target cells....
How Viruses Are Classified andNamed (2)             Program PGMIPABI-FKIP Unsyiah
DNA VIRUS            Program PGMIPABI-FKIP Unsyiah
RNA VIRUS            Program PGMIPABI-FKIP Unsyiah
Modes of Viral Multiplication (1)• General phases in animal virus multiplication cycle:  1. Adsorption - binding of virus ...
Modes of Viral Multiplication (2)General features in the multiplication cycleof an enveloped animal virus. Using an RNAvir...
Adsorption and Host Range (1)• Virus coincidentally collides with a susceptible  host cell and adsorbs specifically to rec...
Adsorption and Host Range (2)The mode by which animal viruses adsorb to the host cell membrane. (a) An envelopedcoronaviru...
Penetration/Uncoating (1)• Flexible cell membrane is penetrated by the  whole virus or its nucleic acid by:  • endocytosis...
Penetration/Uncoating (2)Two principal means by which animal viruses penetrate. (a) Endocytosis (engulfment) anduncoating ...
Program PGMIPABI-FKIP Unsyiah
Replication and Protein Production• Varies depending on whether the virus is a DNA or RNA  virus• DNA viruses generally ar...
Assembly: Filling the capsid• Capsid proteins made in cytoplasm• DNA or RNA gets fills empty capsids• final modifications ...
Release (1)• Assembled viruses leave host cell in one of two ways:  • budding – exocytosis; nucleocapsid binds to membrane...
Release (2)Maturation and release of enveloped viruses. As parainfluenza virus is budded off the membrane, itsimultaneousl...
Program PGMIPABI-FKIP Unsyiah
Damage to Host Cell• Cytopathic effects - virus-induced damage to  cells   1.   Changes in size & shape   2.   Cytoplasmic...
Persistent Infections (1)• Persistent infections - cell harbors the virus  and is not immediately lysed• Can last weeks or...
Persistent Infections (2)• Some animal viruses enter host cell and  permanently alter its genetic material resulting in  c...
Multiplication Cycle inBacteriophages• Bacteriophages – bacterial viruses (phages)• Most widely studied are those that inf...
6 Steps in Phage Replication1.   Adsorption – binding of virus to specific molecule on     host cell2.   Penetration –geno...
Program PGMIPABI-FKIP Unsyiah
Program PGMIPABI-FKIP Unsyiah
Penetration & Release of PhagePenetration of a bacterial cell by a T-even bacteriophage and A weakened bacterial cell, cro...
Lysogeny: The Silent Virus Infection• Not all phages complete the lytic cycle.• Some DNA phages, called temperate phages, ...
Techniques in Cultivating andIdentifying Animal Viruses (1)• Obligate intracellular parasites that require  appropriate ce...
Techniques in Cultivating andIdentifying Animal Viruses (2)                     Cell Culture              Program PGMIPABI...
Techniques in Cultivating andIdentifying Animal Viruses (3)        Cultivating animal viruses in a developing bird embryo ...
Detection of Animal Viral Infections• More difficult than other agents• Consider overall clinical picture• Take appropriat...
Diagnosis            Program PGMIPABI-FKIP Unsyiah
Treatment of viral infections•   The nature of viruses has at times been a major impediment to effective therapy.    • Bec...
Important viruses you should know…• Smallpox (variola major, minor) – complex virus;  inclusions• Herpesviridae – (herpes;...
THANK YOU      Program PGMIPABI-FKIP Unsyiah
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5. introduction to viruses

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5. introduction to viruses

  1. 1. Program PGMIPABIFakultas Keguruan dan Ilmu PendidikanUniversitas Syiah KualaAn Introduction to the Viruses
  2. 2. History (1)• For many years, the cause of viral infections such as smallpox and polio was unknown, even though it was clear that the diseases were transmitted from person to person. • The French bacteriologist Louis Pasteur was certainly on the right track when he postulated that rabies was caused by a “living thing” smaller than bacteria, • in 1884 he was able to develop the first vaccine for rabies. • Pasteur also proposed the term virus to denote this special group of infectious agents. Program PGMIPABI-FKIP Unsyiah
  3. 3. History (2)• The first substantial revelations about the unique characteristics of viruses occurred in the 1890s. • First, D. Ivanovski and M. Beijerinck showed that a disease in tobacco was caused by a virus (tobacco mosaic virus). • Friedrich Loeffler and Paul Frosch discovered a virus that causes foot-and-mouth disease in cattle.• These early researchers found that when infectious fluids from host organisms were passed through porcelain filters designed to trap bacteria, the filtrate remained infectious. Program PGMIPABI-FKIP Unsyiah
  4. 4. History (3)• Over the succeeding decades, a remarkable picture of the physical, chemical, and biological nature of viruses began to take form.• Years of experimentation were required to show that viruses were noncellular particles with a definite size, shape, and chemical composition.• Using special techniques, they could be cultured in the laboratory. • By the 1950s, virology had grown into a multifaceted discipline that promised to provide much information on disease, genetics, and even life itself Program PGMIPABI-FKIP Unsyiah
  5. 5. The Position of Viruses in the BiologicalSpectrum• Viruses are a unique group of biological entities known to infect every type of cell, including bacteria, algae, fungi, protozoa, plants, and animals.• it is best to describe viruses as infectious particles (rather than organisms) and as either active or inactive (rather than alive or dead).• Viruses are different from their host cells in size, structure, behavior, and physiology. • They are a type of obligate intracellular parasite that cannot multiply unless it invades a specific host cell and instructs its genetic and metabolic machinery to make and release quantities of new viruses. Program PGMIPABI-FKIP Unsyiah
  6. 6. Properties of Viruses Program PGMIPABI-FKIP Unsyiah
  7. 7. General Structure of Viruses• As a group, viruses represent the smallest infectious agents.• Their size places them in the realm of the ultramicroscopic . • This term means that most of them are so minute (<0.2 μm) that an electron microscope is necessary to detect them or to examine their fine structures. Program PGMIPABI-FKIP Unsyiah
  8. 8. The Size of VirusesSize comparison of viruses with a eukaryotic cell (yeast) and bacteria. Viruses range from largest (1) to smallest(9). A molecule of a large protein (10) is included to indicate proportion of macromolecules. Program PGMIPABI-FKIP Unsyiah
  9. 9. Viral Components: Capsids, Nucleic Acids,and Envelopes (1)• The general plan of virus organization is the utmost in simplicity and compactness.• Viruses contain only those parts needed to invade and control a host cell: • an external coating and a core containing one or more nucleic acid strands of either DNA or RNA. Program PGMIPABI-FKIP Unsyiah
  10. 10. Viral Components: Capsids, Nucleic Acids,and Envelopes (2) Program PGMIPABI-FKIP Unsyiah
  11. 11. Capsids (1)• All viruses have capsids - protein coats that enclose and protect their nucleic acid.• Each capsid is constructed from identical subunits called capsomers made of protein.• The capsid together with the nucleic acid are nucleoscapsid.• Some viruses have an external covering called envelope; those lacking an envelope are naked. Program PGMIPABI-FKIP Unsyiah
  12. 12. Capsids (2)Generalized structure of viruses. (a) The simplest virus is a naked virus (nucleocapsid) consisting of a geometriccapsid assembled around a nucleic acid strand or strands. (b) An enveloped virus is composed of a nucleocapsidsurrounded by a flexible membrane called an envelope. The envelope usually has special receptor spikes inserted intoit. Program PGMIPABI-FKIP Unsyiah
  13. 13. Capsids (3)• Two structural types: • helical - continuous helix of capsomers forming a cylindrical nucleocapsid • The nucleocapsids of naked helical viruses are very rigid and tightly wound into a cylinder-shaped package. Ex: TMV • Enveloped helical nucleocapsids are more flexible and tend to be arranged as a looser helix within the envelope. Ex: influenza, measles, and rabies viruses • icosahedral - 20-sided with 12 corners • vary in the number of capsomers • a poliovirus has 32, and an adenovirus has 242 capsomers • Each capsomer may be made of 1 or several proteins. Program PGMIPABI-FKIP Unsyiah
  14. 14. Helical capsidsTypical variations of viruses with helical nucleocapsids. Naked helical virus (tobacco mosaic virus):(a) a schematic view and (b) a greatly magnified micrograph. Note the overall cylindrical morphology.Enveloped helical virus (influenza virus): (c) a schematic view and (d) a colorized micrograph featuring apositive stain of the avian influenza virus. This virus has a well-developed envelope with prominent spikestermed H5N1 type. Program PGMIPABI-FKIP Unsyiah
  15. 15. Icosahedral viruses (1) Program PGMIPABI-FKIP Unsyiah
  16. 16. Icosahedral viruses (2)Two types of icosahedral viruses, highly magnified. (a) Upper view: A negative stain of rotaviruseswith unusual capsomers that look like spokes on a wheel; lower view is a threedimensional model of this virus. (b) Herpes simplex virus, a type of enveloped icosahedral virus. Program PGMIPABI-FKIP Unsyiah
  17. 17. Viral envelope• When enveloped viruses (mostly animal) are released from the host cell, they take with them a bit of its membrane system in the form of an envelope. • Some viruses bud off the cell membrane; others leave via the nuclear envelope or the endoplasmic reticulum.• Some proteins form a binding layer between the envelope and capsid of the virus, and glycoproteins (proteins bound to a carbohydrate) remain exposed on the outside of the envelope. • These protruding molecules, called spikes or peplomers, are essential for the attachment of viruses to the next host cell. Program PGMIPABI-FKIP Unsyiah
  18. 18. Functions of Capsid/Envelope• The outermost covering of a virus is indispensable to viral function • it protects the nucleic acid from the effects of various enzymes and chemicals when the virus is outside the host cell.• Capsids and envelopes are also responsible for helping to introduce the viral DNA or RNA into a suitable host cell, • by binding to the cell surface • by assisting in penetration of the viral nucleic acid Program PGMIPABI-FKIP Unsyiah
  19. 19. Complex viruses: atypical viruses (1)• Two special groups of viruses, termed complex viruses are more intricate in structure than the helical, icosahedral, naked, or enveloped viruses just described.• Poxviruses lack a typical capsid and are covered by a dense layer of lipoproteins.• Some bacteriophages have a polyhedral nucleocapsid along with a helical tail and attachment fibers. Program PGMIPABI-FKIP Unsyiah
  20. 20. Complex viruses: atypical viruses (2)Detailed structure of complex viruses. (a) Section through the vaccinia virus, a poxvirus, shows itsinternal components. (b) Photomicrograph and (c) diagram of a T4 bacteriophage. Program PGMIPABI-FKIP Unsyiah
  21. 21. Basic types of viral morphologyA. Complex viruses: (1) poxvirus, a large DNA virus (2) flexible-tailed bacteriophageB. Enveloped viruses: • With a helical nucleocapsid: (3) mumps virus(4) rhabdovirus • With an icosahedral nucleocapsid: (5) Herpesvirus (6) HIV (AIDS)C. Naked viruses: • Helical capsid: (7) plum poxvirus • Icosahedral capsid: (8) Poliovirus ; (9) papillomavirus Program PGMIPABI-FKIP Unsyiah
  22. 22. Nucleic acids (1)• Viral genome – either DNA or RNA but never both• Carries genes necessary to invade host cell and redirect cell’s activity to make new viruses• Number of genes varies for each type of virus – few to hundreds Program PGMIPABI-FKIP Unsyiah
  23. 23. Nucleic acids (2)• DNA viruses • usually double stranded (ds) but may be single stranded (ss) • circular or linear• RNA viruses • usually single stranded, may be double stranded, may be segmented into separate RNA pieces • ssRNA genomes ready for immediate translation are positive-sense RNA. • ssRNA genomes that must be converted into proper form are negative-sense RNA. Program PGMIPABI-FKIP Unsyiah
  24. 24. Other Substances in the VirusParticle• In addition to the protein of the capsid, the proteins and lipids of envelopes, and the nucleic acid of the core, viruses can contain enzymes for specific operations within their host cell.• They may come with preformed enzymes that are required for viral replication. • polymerases that synthesize DNA and RNA and replicases that copy RNA.• The AIDS virus comes equipped with reverse transcriptase for synthesizing DNA from RNA.• However, viruses completely lack the genes for synthesis of metabolic enzymes. • this deficiency has little consequence, because viruses have adapted to assume total control over the cell’s metabolic resources. Program PGMIPABI-FKIP Unsyiah
  25. 25. How Viruses Are Classified andNamed (1)• Classified based on structures, size, nucleic acids, host species, target cells.• 3 orders, 63 families, and 263 genera of viruses• Family name ends in -viridae• Genus name ends in -virus, Simplexvirus, Hantavirus, Enterovirus• Name of genus or family begins with description of virus • appearance: togavirus, coronavirus • place collected: adenovirus, hantavirus • effect on host: lentivirus • acronymns: picornavirus; hepadnavirus Program PGMIPABI-FKIP Unsyiah
  26. 26. How Viruses Are Classified andNamed (2) Program PGMIPABI-FKIP Unsyiah
  27. 27. DNA VIRUS Program PGMIPABI-FKIP Unsyiah
  28. 28. RNA VIRUS Program PGMIPABI-FKIP Unsyiah
  29. 29. Modes of Viral Multiplication (1)• General phases in animal virus multiplication cycle: 1. Adsorption - binding of virus to specific molecule on host cell 2. Penetration - genome enters host cell 3. Uncoating – the viral nucleic acid is released from the capsid 4. Synthesis – viral components are produced 5. Assembly – new viral particles are constructed 6. Release – assembled viruses are released by budding (exocytosis) or cell lysis Program PGMIPABI-FKIP Unsyiah
  30. 30. Modes of Viral Multiplication (2)General features in the multiplication cycleof an enveloped animal virus. Using an RNAvirus (rubella virus), the major events areoutlined, although other viruses will vary inexact details of the cycle. Program PGMIPABI-FKIP Unsyiah
  31. 31. Adsorption and Host Range (1)• Virus coincidentally collides with a susceptible host cell and adsorbs specifically to receptor sites on the cell membrane• Spectrum of cells a virus can infect – host range • hepatitis B – human liver cells • poliovirus – primate intestinal and nerve cells • rabies – various cells of many mammals Program PGMIPABI-FKIP Unsyiah
  32. 32. Adsorption and Host Range (2)The mode by which animal viruses adsorb to the host cell membrane. (a) An envelopedcoronavirus with prominent spikes. The configuration of the spike has a complementary fit for cellreceptors. The process in which the virus lands on the cell and plugs into receptors is termed docking.(b) An adenovirus has a naked capsid that adheres to its host cell by nestling surface molecules on itscapsid into the receptors on the host cell’s membrane. Program PGMIPABI-FKIP Unsyiah
  33. 33. Penetration/Uncoating (1)• Flexible cell membrane is penetrated by the whole virus or its nucleic acid by: • endocytosis – entire virus is engulfed and enclosed in a vacuole or vesicle • fusion – envelope merges directly with membrane resulting in nucleocapsid’s entry into cytoplasm Program PGMIPABI-FKIP Unsyiah
  34. 34. Penetration/Uncoating (2)Two principal means by which animal viruses penetrate. (a) Endocytosis (engulfment) anduncoating of a herpesvirus. (b) Fusion of the cell membrane with the viral envelope (mumps virus). Program PGMIPABI-FKIP Unsyiah
  35. 35. Program PGMIPABI-FKIP Unsyiah
  36. 36. Replication and Protein Production• Varies depending on whether the virus is a DNA or RNA virus• DNA viruses generally are replicated and assembled in the nucleus.• RNA viruses generally are replicated and assembled in the cytoplasm. • Positive-sense RNA contain the message for translation. • Negative-sense RNA must be converted into positive-sense message. Program PGMIPABI-FKIP Unsyiah
  37. 37. Assembly: Filling the capsid• Capsid proteins made in cytoplasm• DNA or RNA gets fills empty capsids• final modifications to capsid • to plug any holes from DNA/RNA entry • to mature the outer proteins Program PGMIPABI-FKIP Unsyiah
  38. 38. Release (1)• Assembled viruses leave host cell in one of two ways: • budding – exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed • lysis – nonenveloped and complex viruses released when cell dies and ruptures• A fully formed, extracellular virus particle that is virulent (able to establish infection in a host) is called a virion• Number of viruses released is variable • 3,000-4,000 released by poxvirus • >100,000 released by poliovirus Program PGMIPABI-FKIP Unsyiah
  39. 39. Release (2)Maturation and release of enveloped viruses. As parainfluenza virus is budded off the membrane, itsimultaneously picks up an envelope and spikes. Program PGMIPABI-FKIP Unsyiah
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  41. 41. Damage to Host Cell• Cytopathic effects - virus-induced damage to cells 1. Changes in size & shape 2. Cytoplasmic inclusion bodies 3. Nuclear inclusion bodies 4. Cells fuse to form multinucleated cells. 5. Cell lysis 6. Alter DNA 7. Transform cells into cancerous cells Program PGMIPABI-FKIP Unsyiah
  42. 42. Persistent Infections (1)• Persistent infections - cell harbors the virus and is not immediately lysed• Can last weeks or host’s lifetime; several can periodically reactivate – chronic latent state • measles virus – may remain hidden in brain cells for many years • herpes simplex virus – cold sores and genital herpes • herpes zoster virus – chickenpox and shingles Program PGMIPABI-FKIP Unsyiah
  43. 43. Persistent Infections (2)• Some animal viruses enter host cell and permanently alter its genetic material resulting in cancer – transformation of the cell.• Transformed cells have increased rate of growth, alterations in chromosomes, and capacity to divide for indefinite time periods resulting in tumors.• Mammalian viruses capable of initiating tumors are called oncoviruses. • Papillomavirus – cervical cancer • Epstein-Barr virus – Burkitt’s lymphoma Program PGMIPABI-FKIP Unsyiah
  44. 44. Multiplication Cycle inBacteriophages• Bacteriophages – bacterial viruses (phages)• Most widely studied are those that infect Escherichia coli – complex structure, DNA• Multiplication goes through similar stages as animal viruses.• Only the nucleic acid enters the cytoplasm - uncoating is not necessary.• Release is a result of cell lysis induced by viral enzymes and accumulation of viruses - lytic cycle. Program PGMIPABI-FKIP Unsyiah
  45. 45. 6 Steps in Phage Replication1. Adsorption – binding of virus to specific molecule on host cell2. Penetration –genome enters host cell3. Replication – viral components produced4. Assembly - viral components assembled5. Maturation – completion of viral formation6. Release – viruses leave cell to infect other cells Program PGMIPABI-FKIP Unsyiah
  46. 46. Program PGMIPABI-FKIP Unsyiah
  47. 47. Program PGMIPABI-FKIP Unsyiah
  48. 48. Penetration & Release of PhagePenetration of a bacterial cell by a T-even bacteriophage and A weakened bacterial cell, crowded with viruses. Program PGMIPABI-FKIP Unsyiah
  49. 49. Lysogeny: The Silent Virus Infection• Not all phages complete the lytic cycle.• Some DNA phages, called temperate phages, undergo adsorption and penetration but don’t replicate.• The viral genome inserts into bacterial genome and becomes an inactive prophage - the cell is not lysed.• Prophage is retained and copied during normal cell division resulting in the transfer of temperate phage genome to all host cell progeny – lysogeny.• Induction can occur resulting in activation of lysogenic prophage followed by viral replication and cell lysis. Program PGMIPABI-FKIP Unsyiah
  50. 50. Techniques in Cultivating andIdentifying Animal Viruses (1)• Obligate intracellular parasites that require appropriate cells to replicate• Methods used: • cell (tissue) cultures – cultured cells grow in sheets that support viral replication and permit observation for cytopathic effect • bird embryos – incubating egg is an ideal system; virus is injected through the shell • live animal inoculation – occasionally used when necessary Program PGMIPABI-FKIP Unsyiah
  51. 51. Techniques in Cultivating andIdentifying Animal Viruses (2) Cell Culture Program PGMIPABI-FKIP Unsyiah
  52. 52. Techniques in Cultivating andIdentifying Animal Viruses (3) Cultivating animal viruses in a developing bird embryo Program PGMIPABI-FKIP Unsyiah
  53. 53. Detection of Animal Viral Infections• More difficult than other agents• Consider overall clinical picture• Take appropriate sample • Infect cell culture – look for characteristic cytopathic effects • Screen for parts of the virus • Screen for immune response to virus (antibodies) Program PGMIPABI-FKIP Unsyiah
  54. 54. Diagnosis Program PGMIPABI-FKIP Unsyiah
  55. 55. Treatment of viral infections• The nature of viruses has at times been a major impediment to effective therapy. • Because viruses are not bacteria, antibiotics aimed at bacterial infections do not work.• While there are increasing numbers of antiviral drugs, most of them block virus replication by targeting the function of host cells. This can cause severe side effects.• Antiviral drugs are designed to target one of the steps in the viral life cycle you learned about earlier in this chapter. • Azidothymide (AZT), a drug used to treat AIDS, targets the nucleic acid synthesis stage. • A newer class of HIV drugs, the protease inhibitors, disrupts the final assembly phase of the viral life cycle.• Another compound that shows some potential for treating and preventing viral infections is a naturally occurring human cell product called interferon• Vaccines that stimulate immunity are an extremely valuable tool but are available for only a limited number of viral diseases Program PGMIPABI-FKIP Unsyiah
  56. 56. Important viruses you should know…• Smallpox (variola major, minor) – complex virus; inclusions• Herpesviridae – (herpes; chicken pox – varicella zoster); chronic latent state  reactivated; nuclear inclusions• HPV – can transform cells; warts  cervical cancer• Hepatovirus (A, B, C)• SARS – coronavirus (like the virus that causes bronchitis); prominent spikes on envelope• influenza – Flu; Type A is the one you’ve had;• Rotavirus – viral food poisoning; vomiting and diarrhea – sometimes concurrently!!• HIV – retrovirus; latency; Program PGMIPABI-FKIP Unsyiah
  57. 57. THANK YOU Program PGMIPABI-FKIP Unsyiah

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