Virology
Core concepts
Organize viruses by genome (DNA/RNA), strandedness, envelope, and replication strategy. DNA viruses replicate in the nucleus (except poxviruses); RNA viruses replicate in the cytoplasm (except influenza and retroviruses). Know the Baltimore classes conceptually: positive-sense RNA is directly translated, negative-sense RNA requires an RNA-dependent RNA polymerase, and retroviruses reverse-transcribe into DNA.
High-yield syndromes
Match virus to disease: herpesviruses (HSV encephalitis, VZV shingles, EBV mononucleosis with heterophile antibodies, CMV in immunocompromised), hepatitis viruses (A/E fecal-oral; B/C/D bloodborne), respiratory viruses (RSV bronchiolitis in infants, influenza with antigenic shift vs. drift), and the hemorrhagic/arboviral group. Understand latency (HSV in ganglia, VZV dorsal root ganglia) and reactivation.
Traps
- Confusing antigenic drift (point mutations, seasonal) with shift (reassortment, pandemics).
- Assuming IgM alone proves acute infection; timing and seroconversion matter.
- Forgetting that live vaccines are contraindicated in pregnancy and severe immunocompromise.
- Mixing up which hepatitis virus requires hepatitis B for replication (hepatitis D).
Worked rule of thumb
For a patient with temporal-lobe encephalitis, think HSV-1; start acyclovir before PCR results return because early treatment improves outcomes. PCR on CSF is the test of choice, and a negative early PCR does not fully exclude disease in the first 72 hours.