VIRUSES CHAPTER 10

What are Viruses? Obligate intracellular parasites Viral components Nucleic acids Capsid Envelope

Viral Shapes and Sizes Helical Polyhedral Spherical (Enveloped)

Infectious Properties Viral Host range From 1 species (polio virus) to many (Influenza virus) Viral specificity From 1 cell type (Hepatitis B virus) to several (CMV in GIT, lungs, spleen) Viral Origins ? Co-evolution with cells ? Degeneration

Virus Classification 108 families so far Classification based upon Pathogens for all life forms Classification based upon Nucleic acid type Single strand vs. double strand chromosome + versus – single strand Enveloped versus “naked"

11 RNA Virus Families + strand RNA virus Family Picornaviridae RNA dependent RNA polymerase makes a - strand intermediate template 3 Genera: Enterovirus Includes poliovirus, Hepatovirus Includes Hepatitis A Rhinovirus Attach to molecules of nasal mucous membranes, cause some colds

Unique RNA Virus Cycle 2 + strands Retroviridae Reverse transcriptase unique enzyme RNA to DNA Provirus synthesis Provirus integrates into host DNA No removal Activation and transcription later produces more viruses Includes HIV

Antisense Virus Rhabdoviridae RNA dependent RNA polymerase makes a Sense strand (+) for mRNA Antisense (-) strand as chromosome Includes rabies virus

ds RNA Chromosome Reoviridae Non-enveloped Cause respiratory and intestinal infections in adults Severe diarrhea in infants caused by Rotavirus Animals may be affected by some members

ds DNA Virus Families Adenoviridae Cause many “colds” Highly stable over pH and temperature changes 10-30% of infant diarrhea Infection may be associated with a rash

ds DNA Viruses (cont.) Herpesviridae > 100 species Latent viruses Herpes simplex virus Varicella virus Epstein Barr virus

ds DNA Viruses (cont.) Papovaviridae Cause skin and genital warts DNA may not be integrated into the host chromosome 13 papilloma viruses are associated with cervical cancer GardasilTM

ss DNA Viruses Parvoviridae ss DNA viruses Unrelated viruses or host genes needed to allow replication Human disease known as 5th disease (Erythrovirus) Canine Parvovirus gastroenteritis Dependovirus genus must coinfect with Adenovirus or Herpesvirus for replication, no human diseases

Emerging Viral Diseases Considerations: Reservoirs in animal populations Vectors Mutation/Recombination frequencies Immunity vs. containment (after rapid air travel of incubating patients)

Viral Replication General Characteristics of Replication Adsorption Penetration (virus or chromosome) Synthesis Maturation Release

Lytic Bacteriophages Virulent T-even bacteriophages

Bacteriophage growth Plaque Assay Virion

DNA Animal Viruses Chromosome replication in host cell nucleus Cytoplasmic ribosomes for viral mRNA translation Viral capsid proteins must return to nucleus for maturation phase Envelope proteins to plasma membrane

RNA Animal Viruses Use RNA-dependent RNA polymerase Cytoplasmic chromosomal replication and protein synthesis + strands always needed for mRNA Chromosome may be + strand or – strand, depends on virus family

Retrovirus Cycle Use RNA-dependent DNA polymerase (Reverse transcriptase) + strand chromosome acts as template for ds DNA provirus Later transcription of provirus allows for virus production

Early Virus Culture Methods Live animals Research Eggs Vaccines Allergies

Cell Cultures for Viral Growth Primary – harvested animals cells Continuous – cancer or immortalized cells

Viral Cytopathic Effects Cytopathy Cell shape/size Cell adhesions (contact inhibition) Transformation (cells divide forever) Teratogenic effects CMV, HSV-1, Rubella TORCH series (Toxoplasma, Others like Chicken pox and Hepatitis B, Rubella, CMV, HSV

Viruses and Cancer Cancer - Triggering of rapid uncontrolled cell division Mechanisms of cancer causation Block of tumor suppression genes Proto-oncogene activation Oncogenes (may be carried by DNA cancer viruses)