Identificación de Virus y Cultivo Celular

Virología

• Viruses are acellular organic particles composed of nucleic acids and proteins, often enclosed in an outer layer, requiring a living host (eukaryotic or prokaryotic) to complete their life cycle.
• They are obligate intracellular parasites.
• Viruses are insensitive to standard antimicrobial agents due to their unique nature and composition.
• Despite independent genetic material, they lack the ability to perform functions necessary for reproduction independently.

Virus Structure

• Virus size ranges from 20 to 300 nanometers. Bacteria, however, typically range from 600 to 2000 nanometers, with some exceptions like Mycoplasma being smaller than some viruses (250nm).
• Viruses consist of:
  • Genetic material (core/genome): a single or multiple strands of DNA or RNA. Viruses never have both DNA and RNA.
  • Protein coat (capsid): protective outer layer composed of capsomeres, determining the morphology.
  • Together, the genome and capsid form the nucleocapsid.
  • Envelope: some viruses have an envelope composed of glycoproteins associated with a lipid bilayer. Viruses with envelopes are susceptible to desiccation, acidic pH, lipid solvents, and bile salts (hence, often not transmitted via fecal-oral route), while non-enveloped viruses are resistant to these factors.
• Virus morphology can be helical, icosahedral, complex, or a mixture of those shapes. Some viruses display a complex structure of head, neck, tail, and baseplate (e.g., bacteriophages).

Virus Replication

• Viruses are intracellular parasites, lacking the metabolic machinery needed for reproduction.
• The viral life cycle follows distinct phases:
  • Attachment/adsorption to host cell receptors.
  • Penetration into the host cell.
  • Replication of viral nucleic acid and protein synthesis.
  • Assembly of new viral particles
  • Release of newly assembled viruses
  • Viral replication can occur through a lytic cycle (cell destruction) or lysogenic cycle (viral DNA integration into host's genome).

Virus Classification

• Viruses are classified based on their genetic material (DNA or RNA), structure (single-stranded or double-stranded), and the method used to produce messenger RNA.
• Baltimore classification system is commonly used, organizing viruses into seven groups based on their genome type and mRNA production.
  • Grouped by DNA or RNA, its stranded nature (single/double), and the mechanism for producing mRNA from the viral genome

Viral Identification

• Identifying viruses differs significantly from identifying bacteria. Viruses replicate only within host cells, requiring cell culture for propagation. Furthermore, they lack the capability to form colonies on culture plates, requiring alternative methods for detection.
• Direct methods involve observing viruses under electron microscopy, detecting viral antigens/proteins using assays (such as ELISA or immunofluorescence), or identifying viral nucleic acid sequences (e.g., PCR).
• Indirect methods focus on detecting host immune responses, like antibodies to specific viral proteins.
• Cultivating viruses in cell cultures is used to study viral replication and to produce viral stocks for further analysis. Certain types of cell cultures, or animal models (with ethical review board approval) may be necessary for virus cultivation.

Clinical Significance and Importance

• Viruses cause various human and animal diseases.
• Rapid diagnostic tests offer faster identification of viruses, essential in the prompt management of infections.
• Virus cultivation and assays in clinical microbiology are critical for accurate diagnostic outcomes.
• Proper sample collection and processing are vital for obtaining representative samples and accurate results.