Microbiology · MU Plovdiv

8. Viruses. Nature and properties. Methods for cultivation. Classification. Rickettsia. Nature and properties. Methods for cultivation. Classification.

Inside: 29 sections · 15 labelled pictures · 4 tables · 31 flashcards · 8 min

Topic 8 of 50 in the MU Plovdiv syllabus for Microbiology (Medicine, Years 2 and 3). The free AceMed note covers it in 22 sections, about 907 words (8 min of reading), with 31 flashcards.

In this note

  1. Viruses – Nature and Properties
  2. I. Definition and General Nature
  3. II. Viral Structure
  4. III. Classification of Viruses
  5. IV. Essential Properties
  6. V. Viral Replication Cycle
  7. VI. Effects of Viruses on Host Cells
  8. VII. Laboratory Cultivation
  9. VIII. Detection and Diagnosis
  10. IX. Resistance and Inactivation
  11. X. Prevention and Control
  12. Genus Rickettsia, Genus Caxiella.
  13. I. General Characteristics
  14. II. Morphology & Life Cycle
  15. III. Virulence Factors
  16. IV. Epidemiology
  17. V. Clinical Manifestations
  18. VI. Diagnosis
  19. VII. Treatment
  20. VIII. Prevention
  21. Genus Coxiella
  22. II. Morphology and Pathogenesis

I. Definition and General Nature

  • Viruses are obligate intracellular parasites — they can only replicate inside living host cells.
  • Composed of nucleic acid (DNA or RNA) enclosed in a protein coat (capsid); some have a lipid envelope.
  • Do not have cellular structures (no ribosomes, mitochondria, or nucleus).
  • Acellular, non-living outside the host — no metabolism or independent replication.
  • Measured in nanometers (20–300 nm range).
  • Specificity: infect specific hosts and often specific tissues (tropism) within the host.

II. Viral Structure

  • Nucleic Acid Core:
  • Either DNA or RNA, never both.
  • DNA: single-stranded (ss) or double-stranded (ds); RNA: ss or ds; positive-sense (+) or negative-sense (−).
  • Can be linear or circular, segmented (e.g., influenza) or non-segmented.
  • Capsid:
  • Protein coat that encloses the genome.
  • Made of capsomeres.
  • Shapes: icosahedral, helical, or complex (e.g., poxviruses).
  • Function: protection and attachment.
  • Envelope (in some viruses):
  • Lipid bilayer derived from the host cell membrane.
  • Embedded with viral glycoproteins (spikes) important for host cell entry and immune evasion.
  • Enveloped viruses are more sensitive to drying, heat, and detergents.

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