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Viruses

This article explores the nature of viruses as obligate intracellular parasites that carry out no metabolic functions and replicate only within host cells. It discusses the structure of viruses, including their nucleic acid, capsid, and envelope, and provides examples of different virus structures. The article also covers viral replication processes, detection and enumeration methods for viruses in water and wastewater, and the transport of viruses in the subsurface.

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Viruses

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  1. Viruses The Interface Between Living and Nonliving

  2. Viruses: Acellular Infectious Agents • All viruses are obligate intracellular parasites: specific hosts • Carry out no metabolic functions • Replication inside a host cell only • Very small colloidal particles: 25-350 nm

  3. Virus Structure • Nucleic acid • May be either DNA or RNA • May be either single or double stranded • Capsid • Outer protein coat surrounding nucleic acid • Composed of individual capsomeres • Envelope • Only in some animal viruses (budding viruses) • Derived from host cell

  4. Examples of Virus Structure

  5. Tobacco Mosaic Virus

  6. Pox Virus

  7. Polio Virus

  8. Phi X174

  9. Structure of Bacteriophages

  10. Lytic Viral nucleic acid enters host Takes over host cell metabolic machinery Synthesis of new viral components Assembly Release of new viral particles Lysogenic Viral nucleic acid enters host Viral NA incorporates into host genome Induction causes viral replication and initiates lytic replication Viral Replication

  11. Viruses in Water and Wastewater

  12. Detection/Enumeration Methods • Plaque/Pock Assay • Inoculate viral suspension into susceptible host and count areas of cell death • Direct counts via EM • Detection of viral nucleic acid: PCR

  13. Plaque Assay

  14. PCR • Polymerase chain reaction • Amplification of a specific sequence of DNA • Taq polymerase

  15. Over 140 types of enteric viruses may be found in fecally contaminated water Hepatitis Rotavirus Norwalk type agent Poliovirus Coxsackievirus Echovirus Adenoviruses Astroviruses Caliciviruses Viruses in Water and Wastewater

  16. Transport of Viruses in the Subsurface

  17. Treatment: Viruses

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