Chapter 13 - Viruses, Viroids, and Prions

Obligatory intracellular parasites

Require living host cells to multiply

Bacteriophages

viruses that infect bacteria

Host Range

The spectrum of host cells a virus can infect

Virion

complete, fully developed viral particle

Capsid

protein coat

Capsomeres

protein coat made of capsid (subunits)

Envelope

lipid, protein, and carbohydrate coating on some viruses

Spikes

projections from outer surface

Helical viruses

hollow, cylindrical capsid

Polyhedral viruses

many-sided

Complex viruses

complicated structures

Viral species

a group of viruses sharing the same genetic information and ecological niche (host)

Plaques

clearings on a lawn of bacteria on the surface of agar

Cytopathic effect (CPE)

Virally infected cells are detected via their deterioration, known as________

Lytic cycle

Phage causes lysis and death of the host cell

Lysogenic cycle

– Phage DNA is incorporated in the host DNA

– Phage conversion

– Specialized transduction

Prophage

Inserted phage DNA into the host cell

Specialized transduction

– Specific bacterial genes transferred to another

bacterium via a phage

– Changes genetic properties of the bacteria

Adenoviridae

– Double-stranded DNA, nonenveloped

▪ Respiratory infections in humans

▪ Tumors in animals

Poxviridae

– Double-stranded DNA, enveloped

– Cause skin lesions

▪ Vaccinia and smallpox viruses (Orthopoxvirus)

Herpesviridae

Double-stranded DNA, enveloped
- HHV-1, HHV-2, ….

Simplexvirus

HHV-1 and HHV-2; cause cold sores

Varicellovirus

HHV-3-; causes chickenpox

Lymphocryptovirus

HHV-4; causes mononucleosis

Cytomegalovirus

HHV-5

Roseolovirus

HHV-6 and HHV-7

Rhadinovirus

HHV-8-; causes Kaposi’s sarcoma

Papovaviridae

– Double-stranded DNA, nonenveloped

▪ Papillomavirus

– Causes warts

– Can transform cells and cause cancer

Hepadnaviridae

– Double-stranded DNA, enveloped

▪ Hepatitis B virus

▪ Use reverse transcriptase to make DNA from RNA

Picornaviridae

– Single-stranded RNA, + strand, nonenveloped

▪ Enterovirus

– Poliovirus and coxsackievirus

▪ Rhinovirus

– Common cold

▪ Hepatitis A virus

Togaviridae

– Single-stranded RNA, + strand, enveloped

▪ Alphavirus

– Transmitted by arthropods; includes

chikungunya

▪ Rubivirus

– Rubella

Rhabdoviridae

– Single-stranded RNA, − strand, one RNA strand

▪ Lyssavirus

– Rabies

▪ Numerous animal diseases

Reoviridae

– Double-stranded RNA, nonenveloped

▪ Reovirus (respiratory enteric orphan)

▪ Rotavirus (mild respiratory infections and

gastroenteritis)

Retroviridae

▪ Lentivirus (HIV)

▪ Oncoviruses

Viroids

short pieces of naked RNA

– Cause potato spindle tuber disease

Virusoids

viroids enclosed in a protein coat

– Only cause disease when plant cell is coinfected with

a virus

Prions

Proteinaceous infectious particles

• Inherited and transmissible by ingestion, transplant, and

surgical instruments

– Spongiform encephalopathies

▪ “Mad cow disease”

▪ Creutzfeldt-Jakob disease (CJD)

▪ Gerstmann-Sträussler-Scheinker syndrome

▪ Fatal familial insomnia

▪ Sheep scrapie

Enterovirus

causative agent of Poliovirus and coxsackievirus

Rhinovirus

causative agent of common cold

Rubivirus

causative agent of Rubella

Alphavirus

Transmitted by arthropods; includes chikungunya

Lyssavirus

causative agent of rabies

Reovirus

respiratory enteric orphan

Rotavirus

mild respiratory infections and gastroenteritis