--- NON-ENVELOPED DNA VIRUSES --- ADENOVIRUSES Background First isolated in 1953 from human adenoid cell cultures. ~100 serotypes exist; at least 47 infect huma
--- NON-ENVELOPED DNA VIRUSES --- ADENOVIRUSES Background First isolated in 1953 from human adenoid cell cultures. ~100 serotypes exist; at least 47 infect humans. Classified into subgroups A–F. Serotypes 1–7 are most common and were the first identified. Structure - Non-enveloped icosahedral capsid, 65–80 nm - dsDNA, 30–38 kbp - Replicates in the nucleus - Encodes 25–30 proteins (15 structural) - Fibers carry viral attachment proteins and act as hemagglutinins - Pentons and fibers carry type-specific antigens Epidemiology - Spread by respiratory droplets, fecal-oral route, hand-to-eye contact, and venereal transmission - Close contact settings (classrooms, military barracks) favor spread - Most infections are asymptomatic — facilitates community spread - Serotypes 1–7 are most prevalent; endemic in pediatric populations - Most children have been infected by at least one type by age 10 Pathogenesis - Local replication → viremia → spread to visceral organs - Has a propensity to become latent in lymphoid tissue (adenoids, tonsils, Peyer's patches) - Reactivation occurs in immunosuppressed patients - Oncogenic in rodents (groups A & B) but NOT in humans Clinical Diseases Syndrome Key Features --- --- Acute Febrile Pharyngitis Pharyngitis ± conjunctivitis; mimics strep in children <3 yrs; flu-like symptoms Pharyngoconjunctival Fever Pharyngitis + conjunctivitis + fever Acute Respiratory Disease (ARD) Fever, cough, pharyngitis, cervical adenitis; serotypes 4 & 7 ; can mimic pertussis Conjunctivitis / EKC Follicular conjunctivitis (nodular palpebral mucosa); swimming pool conjunctivitis; foreign body is a risk factor Gastroenteritis 15% of hospitalized gastroenteritis; serotypes 40–42 cause infant diarrhea Hemorrhagic Cystitis Particularly in immunocompromised hosts Most disease is self-limiting (~2 weeks) . More serious in immunocompromised patients. Laboratory Diagnosis - Sample from the relevant site (e.g., throat swab in pharyngitis) - Fluorescent antibody assays and PCR — detect, type, and group the virus - Cell culture (HeLa cells): lytic infection with characteristic inclusion bodies in 2–20 days; must be distinguished from CMV inclusions - Serology rarely used (epidemiologic purposes only) Treatment & Prevention - No approved antiviral treatment - Live oral vaccines for serotypes 4 & 7 used in military recruits --- PARVOVIRUSES (B19) Background Smallest DNA viruses. Only B19 causes human disease. One serotype known. Structure - Non-enveloped, icosahedral capsid - Single-stranded linear DNA (ssDNA) — unique among the non-enveloped DNA viruses covered - Very small Epidemiology - ~65% of adults have been infected by age 40 - Erythema infectiosum most common in children aged 4–15 years - Adults more likely to develop arthralgia and arthritis - Seasonal: late winter and spring Pathogenesis & Replication - Entry via nasopharynx/upper respiratory tract → viremia → bone marrow - Tropism: targets and is cytolytic for erythroid precursor cells (uses the P blood group antigen as receptor) - Two-stage disease: - Stage 1 (infectious): Viremia, flu-like symptoms, erythrocyte production halted for ~1 week → slight drop in Hb. Person is contagious here. - Stage 2 (symptomatic): Immune-mediated — rash and arthralgia coincide with appearance of virus-specific antibody and immune complex formation. No longer contagious. Clinical Presentations Presentation Population Key Features --- --- --- Erythema Infectiosum (Fifth Disease) Children Prodrome 7–10 days → "slapped cheek" rash → spreads to arms/legs → resolves in 1–2 weeks; relapses common Polyarthritis Adults Hands, wrists, knees, ankles Aplastic Crisis Chronic hemolytic anemia (e.g., sickle cell) Most serious complication ; transient reticulocytopenia lasting 7–10 days + ↓ Hb; life-threatening Chronic Infection Immunocompromised Persistent B19 infection, chronic anemia Hydrops Fetalis Seronegative pregnant women Fetal infection → kills erythrocyte precursors → fetal anemia + congestive heart failure → fetal death; no congenital abnormalities documented Note: B19 is the 5th classic childhood exanthem (after varicella, rubella, roseola, measles). Diagnosis - Culture not practical (virus can't be grown in standard cell lines) - IgM detection or viral DNA by PCR — most sensitive; important in pregnancy to distinguish from rubella - ELISA for B19 IgM and IgG available Treatment & Prevention - No specific antiviral treatment - No human vaccine (vaccines exist for dog/cat parvoviruses) - Supportive care; IVIG may be used in immunocompromised patients with chronic infection --- High-yield comparison: Feature Adenovirus Parvovirus B19 --- --- --- DNA type dsDNA ssDNA Capsid Icosahedral, non-enveloped Icosahedral, non-enveloped Size 65–80 nm Smallest DNA virus Replication site Nucleus Nucleus (erythroid precursors) Key disease ARD, conjunctivitis, gastroenteritis Fifth disease, aplastic crisis Treatment None approved None (IVIG in immunocompromised)