1 / 92

Chapter 25

Chapter 25. Pathogenic RNA Viruses. RNA Viruses. Only infective agents that store genetic information in RNA molecules RNA viruses are categorized by: Their genomic structure Presence of an envelope Size and shape of their capsid Four types of RNA viruses

dalton
Télécharger la présentation

Chapter 25

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 25 Pathogenic RNA Viruses

  2. RNA Viruses • Only infective agents that store genetic information in RNA molecules • RNA viruses are categorized by: • Their genomic structure • Presence of an envelope • Size and shape of their capsid • Four types of RNA viruses • Positive single-stranded RNA (+ssRNA) • Retroviruses (+ssRNA viruses that convert their genome to DNA) • Negative single-stranded RNA (-ssRNA) • Double-stranded RNA (dsRNA)

  3. RNA Viruses • Positive RNA • Acts like mRNA • Can be used by a ribosome to translate protein • Negative RNA • Must first be transcribed as mRNA to be processed by a ribosome

  4. Naked, Positive ssRNA Viruses • Picornaviridae • Smallest of the animal viruses • Picornaviruses that cause human disease are in several genera • Rhinovirus, Enterovirus, and Hepatovirus • Caliciviridae, Astroviridae,and Hepeviridae • Larger than picornaviruses • Cause gastrointestinal disease

  5. Naked, Positive ssRNA Viruses • Common Colds Caused by Rhinoviruses • Cause most cases of the common cold • Infections limited to the upper respiratory tract • A single virus is often sufficient to cause a cold • Virus transmitted by aerosols, by fomites, or via hand-to-hand contact • Most commonly transmitted by direct person-to-person contact • Some immunity can be acquired against serotypes infected with in the past • The number of infections tends to decrease with age

  6. Rhinoviruses, the most common cause of colds Figure 25.1

  7. Naked, Positive ssRNA Viruses • Common Colds Caused by Rhinoviruses • Manifestations of rhinoviruses are usually characteristic • Medications can help relieve the symptoms • Do not reduce the duration of the disease • Handwashing is the most important preventative measure

  8. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Transmitted via the fecal-oral route • Ingestion of contaminated food or water • Via fomites • Oral contact with infected hands or fomites • Infect the pharynx and intestine • Spread via the blood infecting various targets in the body • Three main enteroviruses • Polioviruses, coxsackieviruses, and echoviruses

  9. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Poliomyelitis • Polio is caused by one of three serotypes of poliovirus • Last case of wild-type poliomyelitis in the Americas was in 1979 • Four conditions caused by polioviruses • Asymptomatic infections • Minor polio • Nonparalytic polio • Paralytic polio • Can result in bulbar poliomyelitis

  10. A hospital ward full of mechanical respirators Figure 25.2

  11. Reports of naturally occurring polio in 2009 Figure 25.3

  12. Violinist Itzhak Perlman Figure 25.4

  13. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Poliomyelitis • Postpolio syndrome • Crippling deterioration in the function of polio-affected muscles • Near elimination of polio due to development of two vaccines • Inactivated polio vaccine (IPV) • Developed by Jonas Salk • Oral polio vaccine (OPV) • Developed by Albert Sabin

  14. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Other diseases of enteroviruses • Coxsackieviruses and echoviruses also cause human disease • Infection occurs via the fecal-oral route • Most infections are subclinical or produce mild symptoms

  15. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Other diseases of enteroviruses • Coxsackie A viruses • Produce lesion and fever • Herpangina • Hand-foot-and-mouth disease • Coxsackie B viruses • Associated with myocarditis and pericardial infections • Can be transmitted across the placenta • Echoviruses • Acquired intestinally and can cause meningitis and colds

  16. Lesions characteristic of hand-foot-and-mouth disease Figure 25.5

  17. Naked, Positive ssRNA Viruses • Diseases of the Enteroviruses • Diagnosis, treatment, and prevention • Enterovirus infections usually have mild symptoms • Not diagnosed except in severe cases • No antiviral therapy is effective • Good hygiene and adequate sewage can prevent infections • Effective vaccines are available for hepatitis A and polio

  18. Naked, Positive ssRNA Viruses • Hepatitis A • Hepatitis A virus is the causative agent • Survives on various surfaces and is resistant to common household disinfectants • Transmitted through the fecal-oral route • Signs and symptoms are due to the patient’s immune response • Infection does not cause chronic liver disease • Complete recovery occurs most of the time

  19. Comparison of Hepatitis Viruses Figure 25.3

  20. Naked, Positive ssRNA Viruses • Acute Gastroenteritis • Caliciviruses and astroviruses can cause acute gastroenteritis • Can cause outbreaks in day care centers, schools, and hospitals • Caliciviruses cause diarrhea, nausea, and vomiting • Astroviruses cause diarrhea but no vomiting • No specific treatment except replacement of fluid and electrolytes

  21. Viruses of the families Caliciviridae and Astroviridae Figure 25.6

  22. Naked, Positive ssRNA Viruses • Hepatitis E • Also known as enteric hepatitis • Caused by hepatitis E virus • Formerly classified as a calicivirus • Fatal in 20% of pregnant women • No treatment • Prevent by interrupting the fecal-oral route of transmission

  23. Enveloped, Positive ssRNA Viruses • Togaviridae and Flaviviridae • Enveloped, icosahedral +ssRNA viruses • Arboviruses • Often transmitted by arthropods • Coronaviridae • Enveloped, helical +ssRNA viruses

  24. Togaviruses Figure 25.7

  25. Enveloped +ssRNA coronavirus Figure 25.8

  26. Enveloped, Positive ssRNA Viruses • Diseases of Positive RNA Arboviruses • Zoonoses • Animal diseases that spread to humans • Mosquitoes and ticks transmit arboviruses among animal hosts • Arthropod vectors remain infected • Are a continual source of new infections • Most infections result in mild, flu-like symptoms • Arboviruses can occasionally result in second-stage infections • Encephalitis, dengue fever, and yellow fever

  27. Hosts and transmission of viruses of WEE and EEE Figure 25.9

  28. Human West Nile virus infections in the United States Figure 25.10

  29. Aedes aegypti mosquito Figure 25.11

  30. Pathogenesis of dengue hemorrhagic fever Figure 25.12

  31. Enveloped, Positive ssRNA Viruses • Diseases of Positive RNA Arboviruses • Serological tests often used for diagnosis of arbovirus infections • Supportive care is the only treatment • Vaccines exist for some of the arboviruses • Recommended for people traveling to areas where arboviral diseases are prevalent

  32. Enveloped, Positive ssRNA Viruses • Other Diseases of Enveloped +ssRNA Viruses • Rubella • Also called “German measles” • Rubella virus is the causative agent • One of the five childhood diseases that produces skin lesions • Infection begins in respiratory system but spreads throughout the body • Characterized by a rash of flat, pink to red spots • Infections in children are usually not serious • Adults can develop arthritis or encephalitis • Infection of pregnant women can cause congenital defects • Vaccination effective at reducing the incidence of rubella

  33. The rash of rubella Figure 25.13

  34. The efficacy of vaccination against rubella Figure 25.14

  35. Enveloped, Positive ssRNA Viruses • Other Diseases of Enveloped +ssRNA Viruses • Hepatitis C • Caused by hepatitis C virus (HCV) • Accounts for most non-A, non-B hepatitis in the United States • Spread through needles, organ transplants, and sexual activity • Chronic infection with few if any symptoms • Severe liver damage and liver failure can occur over time • No treatment or vaccine

  36. Enveloped, Positive ssRNA Viruses • Other Diseases of Enveloped +ssRNA Viruses • Diseases of coronaviruses • Named due to the corona-like halo formed by their envelopes • Transmitted via large droplets from the upper respiratory tract • Second most common cause of colds • Severe acute respiratory syndrome • Emerging disease caused by previously unknown coronavirus • No treatment or vaccine is available

  37. Coronaviruses Figure 25.15

  38. Prevention of SARS Figure 25.16

  39. Enveloped, Positive ssRNA Viruses with Reverse Transcriptase • Retroviridae • Studied more than any other group of viruses • Have polyhedral capsids with spiked envelopes • Genomes contain two identical molecules of positive ssRNA • Retroviruses don’t conform to the “central dogma” • Retroviruses transcribe dsDNA from ssRNA using reverse transcriptase • Two types of retroviruses • Viruses that are primarily oncogenic • Viruses that are primarily immunosuppressive

  40. Reverse transcriptase Figure 25.17

  41. Enveloped, Positive ssRNA Viruses with Reverse Transcriptase • Oncogenic Retroviruses • Human T-lymphotrophic virus 1 (HTLV-1) • Identified in patient with adult acute T cell lymphocytic leukemia • HTLV-2 • Causes a rare cancer called hairy-cell leukemia • HTLV-5 has not been linked to cancer • HTLV-1 and HTLV-2 are transmitted via sexual intercourse, blood transfusion, and contaminated needles • No specific antiviral treatment • Infections are chronic, and long-term prognosis of patients is poor

  42. Cytoplasmic membrane extensions in hairy-cell leukemia Figure 25.18

  43. Enveloped, Positive ssRNA Viruses with Reverse Transcriptase • Acquired Immunodeficiency Syndrome • AIDS is not a disease but a syndrome • AID Syndrome • Certain opportunistic or rare infections that occur in the presence of antibodies against HIV and a CD4 white blood cell count below 200 cells/microliter of blood • HIV • Likely arose from mutation of simian immunodeficiency virus • Only replicates in humans • Destroys the human immune system

  44. Characteristics of HIV that challenge the immune system Figure 25.6

  45. Enveloped, Positive ssRNA Viruses with Reverse Transcriptase • Acquired Immunodeficiency Syndrome • Two major types of HIV • HIV-1 is prevalent in the United States and Europe • HIV-2 is prevalent in West Africa • Glycoproteins gp120 and gp41 impede immune clearance of HIV • gp120 exhibits antigenic variability • gp41 promotes fusion of the viral envelope to target cell

  46. The replication cycle of HIV Figure 25.19

  47. Process by which HIV attaches to and enters a CD-4 cell Figure 25.20

  48. The course of AIDS Figure 25.21

  49. Diseases associated with AIDS Figure 25.22

  50. Enveloped, Positive ssRNA Viruses with Reverse Transcriptase • Acquired Immunodeficiency Syndrome • Epidemiology of AIDS • AIDS first recognized in young male homosexuals in the U.S. • AIDS is now found throughout the world • HIV found in blood, semen, saliva, vaginal secretions, and breast milk • Blood and semen more infective than other secretions • Infected fluid must contact a tear or lesion in the skin or mucous membranes • Infected fluids can also be injected into the body

More Related