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TORTORA • FUNKE • CASE Microbiology AN INTRODUCTION EIGHTH EDITION B.E Pruitt & Jane J. Stein Chapter 13, part B Viruses, Viroids, and Prions Attachment, Penetration, and Uncoating Figure 13.14 Release of an enveloped virus by budding Note that the envelope is from the host cell membrane plus any protein the virus directed the cell to make (antigens) Figure 13.20 Multiplication of DNA Virus Papovavirus 1 Virion attaches to host cell 7 Virions are released Host cell DNA Capsid DNA 2 Virion penetrates cell and its DNA is uncoated Cytoplasm 6 Virions mature Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 4 Late transcription; DNA is replicated 3 Early transcription and translation; enzymes are synthesized Figure 13.15 Pathways of Multiplication for RNA-Containing Viruses Compare + strand and strand RNA •+ strand is like mRNA • - strand is complementary to + strand (like a DNA template) Figure 13.17 Multiplication of a Retrovirus Reverse Transcriptase copies RNA code into host DNA Capsid Reverse transcriptase DNA Virus Two identical + stands of RNA 1 Retrovirus penetrates host cell. Host cell DNA of one of the host cell’s chromosomes 5 Mature retrovirus leaves host cell, acquiring an envelope as it buds out. Reverse transcriptase Viral RNA Identical strands of RNA 2 Virion penetrates cell and its DNA is uncoated 4 Transcription of the Viral proteins RNA provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins. Provirus 3 The new viral DNA is tranported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA. Figure 13.19 Cancer • Activated oncogenes transform normal cells into cancerous cells. Protooncogenes - not activated or just a normal gene. • Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. • The genetic material of oncogenic viruses becomes integrated into the host cell's DNA. Oncogenic Viruses • Oncogenic DNA Viruses • Adenoviridae • Oncogenic RNA viruses • Retroviridae • Papovaviridae • Viral RNA is transcribed to DNA which can integrate into host DNA • Hepadnaviridae • HTLV 1 • Heresviridae • Poxviridae • HTLV 2 Oncogenic Viruses Latent and “slow” viral infections • Latent Viral Infections • Virus remains in asymptomatic host cell for long periods • Cold sores, shingles • Persistent Viral Infections • Disease processes occurs over a long period, generally fatal • Subacute sclerosing panencephalitis (measles virus) Prions • Infectious proteins • Inherited and transmissible by ingestion, transplant, & surgical instruments • Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease and mad cow disease • Kuru (Tribes in New Guinea) Prions PrPSc PrPc 1 2 3 4 Lysosome Endosome 5 6 7 8 Figure 13.21 • Plant Viruses • Plant viruses enter through wounds or via insects • Viroids • Viroids are infectious RNA; potato spindle tuber disease Figure 13.22 Some Plant Viruses Table 13.6 Virus Families • Single-stranded DNA, nonenveloped viruses • Parvoviridae • Human parvovirus • Fifth disease • Anemia in immunocompromised patients Double-stranded DNA, nonenveloped viruses • Mastadenovirus • Respiratory infections in humans • Tumors in animals • Viral conjuncitivitis Double-stranded DNA, nonenveloped viruses • Papillomavirus (human wart virus) • Polyomavirus • Cause tumors, some cause cancer Double-stranded DNA, nonenveloped viruses • Orthopoxvirus (vaccinia and smallpox viruses) • Molluscipoxvirus • Smallpox, molluscum contagiosum, cowpox Double-stranded DNA, nonenveloped viruses • Simplexvirus (HHV1 and HHV 2) • Varicellavirus (HHV 3) • Lymphocryptovirus (HHV 4) • Cytomegalovirus (HHV 5) • Roseolovirus (HHV 6) • HHV 7 • Kaposi's sarcoma (HHV 8) • Some herpesviruses can remain latent in host cells Double-stranded DNA, nonenveloped viruses • Hepadnavirus (Hepatitis B virus) • Use reverse transcriptase to produce DNA from mRNA Single-stranded RNA, + strand, nonenveloped • Enterovirus • Enteroviruses include poliovirus and coxsackievirus • Rhinovirus • Hepatitis A virus Single-stranded RNA, + strand, nonenveloped • Hepatitis E virus • Norovirus (Norwalk agent) causes gastroenteritis Single-stranded RNA, + strand, nonenveloped • Alphavirus • Alphaviruses are transmitted by arthropods; include EEE, WEE • Rubivirus (rubella virus) Single-stranded RNA, + strand, nonenveloped • Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses • Hepatitis C virus Single-stranded RNA, + strand, nonenveloped • Coronavirus • Upper respiratory infections Single-stranded RNA, – strand, one RNA strand • Vesiculovirus • Lyssavirus (rabies virus) • Cause numerous animal diseases Single-stranded RNA, – strand, one RNA strand • Filovirus • Enveloped, helical viruses • Ebola and Marburg viruses Marburg kills BBC Single-stranded RNA, – strand, one RNA strand • Paramyxovirus • Morbillivirus • Paramyxovirus causes measles • parainfluenza, mumps and Newcastle disease Single-stranded RNA, – strand, one RNA strand • Hepatitis D virus • Depends on coinfection with Hepadnavirus Single-stranded RNA, – strand, multiple RNA strands • Influenzavirus (Influenza viruses A and B) • Influenza C virus • Envelope spikes can agglutinate RBCs Single-stranded RNA, – strand, multiple RNA strands • Bunyavirus (CE virus) • Hantavirus Single-stranded RNA, – strand, multiple RNA strands • Arenavirus • Helical capsids contain RNAcontaining granules • Lymphocytic choriomeningitis • VEE and Lassa Fever Single-stranded RNA, two RNA strands, produce DNA • Lentivirus (HIV) • Oncogenic viruses • Use reverse transcriptase to produce DNA from viral genome • Includes all RNA tumor viruses Double-stranded RNA, nonenveloped • Reovirus (Respiratory Enteric Orphan) • Rotavirus • Mild respiratory infections and gastroenteritis • Colorado tick fever