Viruses and Disease: How Infections Work

Viruses are obligate intracellular pathogens: nucleic acid (DNA/RNA) + protein capsid ± envelope.

Infection Cycle

1. Attachment → entry (receptor-mediated endocytosis/fusion).
2. Uncoating → genome release.
3. Replication (viral polymerase) + transcription/translation (host machinery).
4. Assembly → egress (lysis or budding).

Disease Spectrum

• Mild: rhinovirus (cold), norovirus (gastroenteritis).
• Severe: influenza, measles, SARS-CoV-2, HIV, Ebola, rabies.
• Oncogenic: HPV, HBV, HCV, EBV, HTLV-1, KSHV.

Treatment & Prevention

• Antivirals target specific viral enzymes (neuraminidase, polymerase, protease, integrase).
• Vaccines: live-attenuated, inactivated, mRNA, vector – induce neutralizing antibodies/T-cells.
• Supportive care for most acute infections.

Antibiotics are ineffective against viruses.