Viruses and Their Replication

Viruses

• Viruses are infectious microbes made of a segment of nucleic acid (DNA or RNA) surrounded by a protein coat.
• Viruses cannot replicate alone and need to enter a cell to reproduce.
• During reproduction, a virus injects its genetic material (DNA or RNA) into the host cell, altering the cell's metabolic processes to benefit the virus.
• Due to their reliance on host cells, viruses are difficult to target with drugs.
• Some antiviral therapies are available for influenza A, herpes, CMV, HIV, hepatitis B and C viruses, and some viruses causing warts and eye infections.

Stages of Viral Replication

• Viruses cannot replicate alone.
• They must attach to and enter a host cell.
• Inside the host cell, viruses utilize the cell's energy to synthesize proteins, DNA, and RNA.
• Viruses are challenging to eliminate because they live inside our cells.

Common Respiratory Viruses

• Common respiratory viruses include influenza A, influenza B, and respiratory syncytial virus (RSV).
• They can cause cough, fever, inflammation of the nasal mucosa, and inflammation of the respiratory tract.

Other Common Viruses

• Herpes Virus: Causes painful vesicles (blisters) in clusters on the skin, cornea, or mucous membranes. Primary infection lasts about 2 weeks, while the duration of recurrences varies.
• Cytomegalovirus (CMV): May cause no symptoms. Can lead to fatigue, nausea, and jaundice. If contracted during pregnancy, it can cause stillbirth, brain damage, or birth defects.
• Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS): HIV attacks helper T cells.
  • Acute infection: Characterized by fever, rash, and muscle aches.
  • Asymptomatic infection: Follows acute infection; duration is variable.
  • Persistent generalized lymphadenopathy: Swollen lymph nodes for more than 3 months.
  • Constitutional symptoms: Fever lasting longer than a month, unintended weight loss, and persistent fatigue.
  • Neurological disease: Dementia.
  • Secondary infections: Such as Pneumocystis carinii pneumonia and disseminated herpes simplex.

Antiviral Therapy

• Antiviral drugs are used to treat viral diseases, including those caused by warts and the common cold.
• Antivirals have the following characteristics:
  • They are able to enter cells infected with a virus.
  • They can interfere with viral nucleic acid synthesis and regulation.
  • Some antivirals block the virus from attaching to cells.
  • Some antivirals stimulate the body's immune system.

Viruses That Respond to Antiviral Therapy

• Influenza A and some respiratory viruses.
• Herpes viruses.
• Cytomegalovirus (CMV).
• HIV (retroviral agents).
• Hepatitis B and C (retroviral agents).
• Viruses that cause warts and eye infections.

Retroviral Agents

• Used to treat HIV/AIDS.