Viruses and Their Replication

Study Notes

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.

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 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.

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 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.