Introduction to Virology – 1

  • Virus is an obligate intracellular parasite containing genetic material surrounded by proteins
  • Not living organisms, cannot produce energy or synthesize proteins independently, host cell machinery is needed
  • Viruses that infect bacteria are called bacteriophages

Naked virus, enveloped virus

Difference between Naked Virus and Enveloped Virus

Properties Enveloped Naked
Environmental stability Are destroyed by acids, detergents and drying (easily die) Stable to temperaure, acids, proteases, disinfectants and drying
Release from cell Budding Lysis
Spread to host Spreads in large droplets, secretions, transplanted organs, blood transfusions Spread easily by direct contact, dust, small air droplets
Stability outside cells Must stay wet Can dry out and retain infectivity
Effective immune respone May need antibody and cell mediated immunity for protection Antibodies are sufficient

Difference between bacteria and viruses



Obligate intracellular parasites Free living, can be parasitic
No ribosomes Has ribosomes
DNA or RNA, not both DNA and RNA
Need electronic microscopes Seen in light microscopes
10-100 genes 100-1000 genes
Tangled phylogeny Natural phylogeny

Baltimore Classification of Viruses

Baltimore classification of virus

Replication of viruses

Image result for replication of viruses

All RNA viruses replicate in the cytoplasm except Orthomyxoviruses and Retroviruses that have replicative stages in nuclei

All DNA viruses replicate in the cytoplasm except Poxviruses that can replicate in the cytoplasm.

Image result for effect of animal viruses on cells