MicrobioLec8 Recording

Viral Life Cycle

• Viruses must enter host cells to reproduce.

  • Main mechanisms: penetration and uncoating of nucleic acids.

  • If viral RNA, it may have reverse transcriptase to convert RNA to DNA.

Steps of Viral Replication

1. Adsorption

   • Virus attaches to receptors on the host cell.

2. Penetration and Uncoating

   • Viral nucleic acid enters the host cell and the capsid is disassembled.

3. Replication

   • Nucleic acid (either RNA or DNA) is replicated.

   • Viral proteins encoded in nucleic acid are synthesized (e.g., capsid proteins).

4. Assembly and Maturation

   • Newly replicated viral components are assembled into new virions.

5. Release

   • Viruses can exit the host cell through two mechanisms:

     • Lytic release: host cell explodes releasing virions.

     • Budding: host cell remains intact and continuously expels new virions.

       • In this case, the host cell becomes a virus-producing factory.

Viral Diagnostics

• Two main approaches to detect viruses:

  1. Direct Detection of Virus

     • Electron Microscopy: Allows visualization of viruses due to their small size.

     • Cell Culture: Virus is cultured in cells.

  • Observe cytopathic effects or changes due to viral infection.

  2. Detection of Immune Response

     • Indirect ELISA: Detects antibodies in the patient’s serum to determine if they have an immune response to the virus.

Methods of Direct Virus Detection

• Electron Microscopy

  • Use high magnification to visualize viral particles from clinical specimens (e.g., CSF, stool) on a copper grid.

• Cell Culture

  • If virus causes lysis of cells, characteristic changes can be observed under the microscope.

    • Is the basis for counting infectious units per mL.

• Immunofluorescence

  • Used when the virus does not lyse the host cell. Antibodies are used to detect viral proteins in host cells.

• Red Blood Cell Agglutination

  • Some viruses can agglutinate red blood cells, which can be used for detection (e.g., adenovirus).

Limitations in Virus Detection

• Some infections may not show symptoms.

• Variability in immune response complicates detection of antibodies.

Influenza Virus

• Influenza is characterized by two major surface antigens, hemagglutinin (H) and neuraminidase (N).

  • Variability leads to classification (e.g., H1N1, H5N1).

  • Hemagglutinin can cause red blood cells to clump, useful for diagnosis.

• Vaccination against influenza is recommended annually due to antigenic drift.

Parainfluenza Virus

• Affects primarily infants and young children, causing croup (barking cough).

• No vaccine available.

Rhinovirus (Common Cold)

• Causes upper respiratory infections with many serotypes complicating vaccine development.

Coronavirus (COVID-19)

• Characterized by a spike protein that binds ACE receptors.

• Vaccines developed using mRNA technology, which allows for rapid antigen delivery to elicit immune response.

• Variant tracking is essential for addressing changing strains.

Enteric Viruses

• Rotavirus (common in children under 18): causes diarrhea; has a vaccine.

• Norovirus (common in adults): also causes diarrhea; no vaccine available.

• These viruses replicate in the intestinal tract causing gastrointestinal symptoms.

Poliovirus

• Causes poliomyelitis, leading to paralysis; eradication efforts ongoing, but remain hindered by social factors.

• Two vaccines:

  • Salk vaccine (inactivated) for immunocompromised patients.

  • Sabin vaccine (live attenuated) preferred for healthy individuals.

Coxsackie Virus

• Causes aseptic meningitis, hand, foot, and mouth disease, and pleurodynia (devil's grip).

Rash-Causing Viruses

• Measles: Highly contagious; diagnostic symptoms include Koplik spots and a blotchy rash.

• Rubella (German measles): Short-lived rash; highly dangerous for pregnant individuals.

• Varicella Zoster Virus: Causes chickenpox in children, can reactivate as shingles in adults.

Herpes Simplex Virus (HSV)

• HSV-1 causes cold sores; HSV-2 causes genital herpes.

• Both remain dormant in the body and can reactivate.

Human Papillomavirus (HPV)

• Causes warts and certain cancers; vaccines recommended prior to sexual activity.