Respiratory Viruses Flashcards
Three types of RNA viruses
Positive stranded, negative stranded, retroviruses. If positive, similar to RNA, if negative, transcription must occur first.
Retroviruses
RNA is first transcribed to DNA. Transcription, translation, and replication often occur in the cytoplasm.
Paramyxovirus structure
Negative sense, single stranded, nonsegmented RNA. Helical nucleocapsid with three proteins NP, polymerase phosphoprotein, large protein. Matrix protein lines lipid bilayer inside the viron envelope. Lipid bilayer studded with glycoproteins, fusion protein, attachment proteins
NP, P, L, M, F, HN, H, G
Nucleoprotein, polymerase phosphoprotein, large protein, matrix protein, fusion protein, attachment proteins.
How does the paramyxovirus replicate?
Attachment proteins bind to sialic acid on host cell surface, genome transcribed into individual mRNAs and full length positive sense RNA template. Nucleocapsid associates with matrix and plasma membranes and leaves the cell by budding.
Parainfluenza virus
Primarily affects young children, causing upper and lower respiratory tract infections like croup, common cold, bronchiolitis, pneumonia
HPIV1
Causes croup along with HPIV2, both occur in fall
HPIV 3
primarily causes pneumonia and bronchiolitis. Throughout the year, but peak in spring.
Pathogenesis of HPIV
Infects the nasal and pharyngeal mucosal epithelia then spreads locally along the respiratory epithelium to the larynx and trachea.
Anatomic hallmark of croup?
Steeple sign = narrowing of the trachea in the subglottic region.
Transmission of parainfluenza virus
Spread via respiratory droplets or direct person to person contact with infected secretions.
Diagnosis of parainfluenza virus
Antigen detection (direct fluorescent Ab, ELISA), cell culture, PCR
Treatment of HPIV
Self-limited infection, treatment is primarily supportive (dexamethasone, epinephrine)
RSV Virus Clinical Syndromes
Bronchiolitis or pneumonia, most patients have upper respiratory disease, more serious manifestation involving the lower respiratory tract in older children/adults
Who is at increased risk for RSV infection?
Preterm birth, cyanotic or complicated congenital heart disease (esp. pulm hypertension), immunodeficiency, old age
Pathogenesis of RSV
Replicates in nasopharynx, then infects the bronchiolar epithelium. Extends to the alveolar pneumocytes by cell to cell spread, aspiration of secretions and formation of syncytia. Necrosis of bronchi and bronchioles results in mucus plugs, fibrin, and necrotic material. Immune response to RSV seems to play a role in the pathogenesis and severity of bronchiolitis.
Treatment for RSV
Supportive, ribavirin
Ribavirin
Nucleoside analog that inhibits nucleic acid synthesis
Palivizumab
Monoclonal antibody against F protein, used for high risk infants
Human metapneumovirus
2nd leading cause of bronchiolitis in infants, causes 15% of common colds in children, also can cause pneumonia, croup, upper respiratory tract infections
Who is at risk for contracting hMPV?
Immunocompromised, preterm birth, transplant, cardiopulmonary disease.
Transmission of hMPV?
Direct or close contact with contaminated secretions. Nosocomial infections have been reported.
When does hMPV infection peak?
Late winter/early spring in temperate climates.
Can hMPV be grown in culture?
Yes, but it has a very long incubation period and is difficult to grow.
