Herpesviruses
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Direct answer
Eight human herpesviruses share one signature: double-stranded DNA in an icosahedral capsid, an envelope, and latency for life after primary infection. HSV-1 and HSV-2 (HHV-1, 2) hide in sensory ganglia and surface as recurrent ulcers; varicella-zoster (HHV-3) waits in dorsal root ganglia for dermatomal shingles; Epstein–Barr virus (HHV-4) latently infects B lymphocytes through the CD21 receptor and drives infectious mononucleosis, Burkitt lymphoma and nasopharyngeal carcinoma; CMV (HHV-5), the largest of the family, enlarges infected cells into owl's-eye inclusions and is the leading congenital viral infection; HHV-6 causes roseola; HHV-8 causes Kaposi sarcoma.
What you must remember
- Herpes simplex: gingivostomatitis and keratitis (dendritic ulcer, type 1), genital herpes (type 2), herpetic whitlow, neonatal infection during passage; multinucleated giant cells on a Tzanck smear and Cowdry type A inclusions are cytopathic hallmarks; latency in trigeminal and sacral ganglia; acyclovir is the drug.
- Varicella-zoster: primary chickenpox with crops of lesions at different stages ("dew drop on rose petal") in a centripetal distribution, then dermatomal zoster decades later; latency in dorsal root ganglia; live attenuated vaccine; acyclovir for disease, especially in immunocompromised patients.
- EBV: infectious mononucleosis — fever, pharyngitis, posterior cervical lymphadenopathy, splenomegaly; Downey cells are atypical T lymphocytes; heterophile antibodies detected by the Paul–Bunnell or Monospot test (agglutinate sheep red cells, absorbed by ox but not guinea-pig cells); VCA IgM marks acute infection; associated with endemic Burkitt lymphoma (c-myc translocation, malaria co-factor), nasopharyngeal carcinoma and oral hairy leukoplakia in AIDS.
- CMV: owl's-eye intranuclear inclusions with a narrow rim of cytoplasm; congenital infection — periventricular intracranial calcification, sensorineural hearing loss, "blueberry muffin" purpura, jaundice with thrombocytopenia; retinitis when CD4 falls below 50; pp65 antigenaemia or viral load for disease activity; ganciclovir or valganciclovir for treatment.
- HHV-6: roseola infantum (exanthem subitum) — high fever for three to five days, and the rash appears as the fever falls; febrile seizures complicate.
- HHV-8: Kaposi sarcoma in HIV — spindle-cell angioproliferative tumours.
- Family logic: all are enveloped, so ether-sensitive and spread in secretions; all establish latency — the unifying answer when the stem asks "which virus family recurs".
A typical exam case
A 19-year-old has a week of fever, marked pharyngitis with palatal petechiae, bulky posterior cervical nodes and new jaundice after a course of ampicillin. The stem is infectious mononucleosis: lymphocytosis with atypical lymphocytes on smear, a positive Monospot, and the ampicillin rash — the patient is not allergic, the rash is EBV-driven. Contrast a CMV mononucleosis in an older patient: heterophile-negative, with less pharyngitis and more fever; diagnosis is CMV IgM or viral load. Now move to a newborn with microcephaly, periventricular calcification and petechiae — think TORCH with CMV on top of the list for calcifications of that pattern, confirm by urine or saliva PCR in the first three weeks of life, and remember ganciclovir for symptomatic congenital disease.
Where students slip
Latency sites are asked straight: HSV in sensory (trigeminal, sacral) ganglia, VZV in dorsal root ganglia, EBV in B lymphocytes — candidates mix them under time pressure. The ampicillin rash in mononucleosis is misread as drug allergy, and the Tzanck smear is credited to VZV and HSV only, not to CMV, whose signature is the owl's-eye inclusion. Finally, roseola's rash-after-defervescence sequence is the opposite of measles, where Koplik spots and rash arrive while fever persists.
Frequently asked questions
What does a Tzanck smear show in herpes infection?
Multinucleated giant cells with moulded nuclei and marginated chromatin, indicating HSV or VZV infection; it cannot distinguish the two, unlike PCR or type-specific serology.
Which test confirms acute EBV infectious mononucleosis?
Heterophile antibodies by the Paul–Bunnell or Monospot test, supplemented by VCA IgM when heterophile is negative, as happens in younger children.
How does congenital CMV classically present?
Periventricular intracranial calcification, sensorineural hearing loss, chorioretinitis, thrombocytopenic purpura and jaundice — it is the commonest congenital viral infection.
Where does varicella-zoster remain latent?
Dorsal root ganglia, from which reactivation travels one dermatome as shingles; pain may precede the vesicles by days.
Which herpesvirus causes Kaposi sarcoma?
Human herpesvirus 8, essential for the angioproliferative tumour that appears typically in advanced HIV infection.