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# Viral Evolution ## Genetic Shift Occurs when a cell is infected by two different segmented viruses (e.g., swine influenza and human influenza viruses). RNA segment reassortment happens between the viruses, leading to a dramatically different virus. This process is responsible for major global out...

# Viral Evolution ## Genetic Shift Occurs when a cell is infected by two different segmented viruses (e.g., swine influenza and human influenza viruses). RNA segment reassortment happens between the viruses, leading to a dramatically different virus. This process is responsible for major global outbreaks (pandemics), as the new strain is substantially different from previous strains. ## Anti-Genetic Shift Refers to random mutations in the hemagglutinin (HA) or neuraminidase (NA) genes of the virus. These mutations lead to minor changes in the HA or NA proteins, resulting in small variations of the virus. This causes local seasonal outbreaks (epidemics) rather than global pandemics. # Different Viruses ## Influenza Viruses ### Characteristics: - Orthomyxoviruses. - Enveloped, - Negative ssRNA viruses with segmented genome. ### Risk Factors - Patients at risk for fatal bacterial superinfection - *S aureus* - *S pneumoniae* - *H influenzae*. ### Treatment: - Supportive +/- neuraminidase inhibitor (eg, oseltamivir, zanamivir). ## Rubella Virus ### Causes Causes rubella, formerly called German (3-day) measles. ### Presentation - Fever - Postauricular - Other lymphadenopathy - Arthralgias - Fine, maculopapular rash that starts on face and spreads centrifugally to involve trunk and extremities ### Congenital Rubella Causes mild disease in children but serious congenital disease (a TORCH infection). - Classic Triad - Sensorineural deafness - Cataracts - Patent ductus arteriosus. - Dermatological Manifestation "Blueberry muffin" appearance may be seen due to dermal extramedullary hematopoiesis ## Paramyxoviruses - Paramyxoviruses cause disease in children. ### Examples - Parainfluenza (croup) - Mumps - Measles, - RSV - Human metapneumovirus. ### Characteristics - All subtypes can cause respiratory tract infection (bronchiolitis, pneumonia) in infants. - All contain surface F (fusion) protein, which causes respiratory epithelial cells to fuse and form multinucleated cells. ### Treatment - Palivizumab (monoclonal antibody against F protein) prevents pneumonia caused by RSV infection in premature infants. - Palivizumab for paramyxovirus (RSV) prophylaxis in preemies ## Acute Laryngotracheobronchitis Also called croup. ### Viral Factors - Hemagglutinin (binds sialic acid and promotes viral entry) - Neuraminidase (promotes progeny virion release) antigens. ### Presentation - Results in a "seal-like" barking cough and inspiratory stridor. - Narrowing of upper trachea and subglottis leads to characteristic steeple sign on x-ray ## Measles (Rubeola) Virus ### Presentation - Prodromal fever with cough - Coryza - Conjunctivitis - Koplik spots (bright red spots with blue-white center on buccal mucosa A), followed 1-2 days later by a maculopapular rash that starts at the head/neck and spreads downward. - Lymphadenitis with Warthin-Finkeldey ### Characteristic - Giant cells (fused lymphocytes) in a background of paracortical hyperplasia. ### Possible sequelae: - Subacute sclerosing panencephalitis (SSPE): personality changes, dementia, autonomic dysfunction, death (occurs years later) - Encephalitis (1:1000): symptoms appear within few days of rash - Giant cell pneumonia (rare except in immunosuppressed) ### Treatment - Vitamin A supplementation can reduce morbidity and mortality from measles, particularly in malnourished children. ## Mumps Virus - Uncommon due to effectiveness of MMR vaccine ### Presentation - Parotitis - Orchitis (inflammation of testes) - Aseptic Meningitis, and - Pancreatitis. - Can cause sterility (especially after puberty). ## Receptors used by Viruses | Virus | Receptors | |---|---| | CMV | Integrins (heparan sulfate) | | EBV | CD21 | | HIV | CD4, CXCR4, CCR5 | | Parvovirus B19 | P antigen on RBCS | | Rabies | Nicotinic AChR | | Rhinovirus | ICAM-1 | | SARS-CoV-2 | ACE2 |