Viruses, Viroids, and Prions Chapter 13, part B Viruses, Viroids, and Prions

Attachment, Penetration, and Uncoating Figure 13.14

Release of an enveloped virus by budding 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 6 Virions mature Cytoplasm Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 3 Early transcription and translation; enzymes are synthesized 4 Late transcription; DNA is replicated Figure 13.15

Pathways of Multiplication for RNA-Containing Viruses Figure 13.17

Multiplication of a Retrovirus Reverse transcriptase Capsid 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 2 Viral RNA Virion penetrates cell and its DNA is uncoated Identical strands of RNA 4 Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins. Viral proteins RNA 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. Provirus Figure 13.19

Cancer Activated oncogenes transform normal cells into cancerous cells. 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 Heresviridae Poxviridae Papovaviridae Hepadnaviridae Oncogenic RNA viruses Retroviridae Viral RNA is transcribed to DNA which can integrate into host DNA HTLV 1 HTLV 2

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, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease PrPC, normal cellular prion protein, on cell surface PrPSc, scrapie protein, accumulate in brain cells forming plaques

Prions PrPSc PrPc 1 2 3 4 Lysosome Endosome 5 6 7 8 Figure 13.21

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

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

Single-stranded RNA, – strand, one RNA strand Paramyxovirus Morbillivirus Paramyxovirus causes 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 RNA-containing 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