Orthomyxoviruses Notes

NOTES NOTES ORTHOMYXOVIRUSES GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Associated clinical syndromes: influenza (“the flu”), pneumonia ▪ RNA virus family; causes acute respiratory disease Genetic material ▪ Negative-sense, single-stranded RNA Taxonomy ▪ Genera ▫ Influenza A, Influenza B, Influenza C: infect humans ▫ Influenza D, Isavirus, Thogotovirus, Quaranjavirus ▪ Classified by surface protein ▫ Influenza A, B: hemagglutinin (H) (glycoprotein, allows progeny release); neuraminidase (N) (lectin; binds to host cell through sialic acid residues) ▫ Influenza C: hemagglutinin esterase fusion (F) (binds to host cell) Morphology ▪ Enveloped (outer lipid membrane) ▪ Spherical/filamentous ▪ Size: 50–120nm 472 OSMOSIS.ORG SIGNS & SYMPTOMS ▪ Fever, malaise, myalgia, sore throat, nonproductive cough DIAGNOSIS ▪ Clinical examination DIAGNOSTIC IMAGING X-ray ▪ Chest CT scan LAB RESULTS ▪ Molecular assays ▪ Viral culture TREATMENT MEDICATIONS ▪ Antiviral therapy

Chapter 85 Orthomyxoviruses INFLUENZA VIRUS osms.it/influenza PATHOLOGY & CAUSES ▪ Single-stranded RNA virus; causes acute respiratory disease ▪ AKA “the flu” ▪ Incubation: 1–4 days Pathogenesis ▪ Influenza virus penetrates upper respiratory tract → hemagglutinin binds to epithelial cell sialic acid residue → endocytosis → viral replication → neuraminidase releases progeny → viral infection spreads ▪ Viral shedding (progeny release) ▫ Duration: average 4–8 days ▫ Magnitude: ↑ symptoms = ↑ shedding ▪ Influenza A antigen variations → immune evasion, reinfection ▫ Antigenic shift: major changes in H/N proteins (two different influenza virus genome segments reassort) → epidemic/pandemic ▫ Antigenic drift: minor changes in H/N proteins (mutation in H/N gene) → outbreak Taxonomy ▪ Nomenclature: [type] / [original host] / [location of first identification] / [strain number] / [year of origin] ([subtype]) ▫ Host type, subtype included in influenza A viruses only ▫ E.g. H1N1 type A flu virus of duck origin, found in Alberta, Canada, 35th strain, found in 1976 → A/duck/ Alberta/35/76(H1N1) Pandemics, associated strains ▪ 1918 “Spanish flu” → H1N1 ▪ 1957 “Asian flu” → H2N2 ▪ 1968 “Hong Kong flu” → H3N2 ▪ 2009 (worldwide) → H1N1 RISK FACTORS ▪ Immunosuppression, age ≥ 65 years, age < six months, nursing/chronic care facility resident, pregnancy, chronic disease, morbid obesity COMPLICATIONS ▪ Secondary bacterial infection (e.g. pneumonia, sinusitis, otitis media, bronchiolitis), acute respiratory distress syndrome, myositis, rhabdomyolysis, myocarditis, pericarditis, encephalitis ▪ Secondary bacterial infections generally due to Streptococcus pneumoniae SIGNS & SYMPTOMS Uncomplicated influenza ▪ Systemic: fever, malaise, myalgia, headaches, weakness, dizziness ▪ Respiratory: non-productive cough, sore throat, nasal secretion ▪ Mild cervical adenopathy Complicated influenza ▪ Primary influenza pneumonia: fever, dyspnea, cyanosis ▪ Secondary bacterial pneumonia: fever, cough, purulent sputum Transmission ▪ Direct contact, airborne droplets, fomites Outbreak ▪ Abrupt ▪ Winter; year-round in tropical regions ▪ Duration: 2–3 months OSMOSIS.ORG 473

DIAGNOSIS ▪ Clinical examination, during outbreak DIAGNOSTIC IMAGING X-ray ▪ chest CT scan ▪ Primary influenza pneumonia: bilateral reticular/reticulonodular opacities, sometimes consolidation ▪ Secondary bacterial influenza: pulmonary infiltrates LAB RESULTS ▪ Respiratory tract specimen molecular assay: reverse-transcriptase polymerase chain reaction (RT-PCR) ▪ Rapid antigen test: immunoassay ▪ Respiratory tract specimen viral culture 474 OSMOSIS.ORG TREATMENT MEDICATION ▪ Severe illness/risk factors → antiviral therapy ▫ Neuraminidase inhibitors; H1N1 commonly resistant ▫ M2 proton channel inhibitors; active against influenza A only ▪ Symptomatic treatment: acetaminophen, non-steroidal anti-inflammatory drugs (NSAID) ▪ Secondary bacterial infection: antibiotics OTHER INTERVENTIONS ▪ Hydration Prevention ▪ Vaccine ▫ Inactivated (intramuscular/intradermal)/ live attenuated (intranasal); trivalent/ quadrivalent (2 influenza A antigens + 1/2 influenza B antigens); annual, single-dose application (before winter); age ≥ six years ▪ Antiviral prophylaxis (high-risk individual) ▫ Neuraminidase inhibitors ▪ Infection control ▫ E.g. hand hygiene, face mask