Flashcards in Respiratory Viruses Deck (40):
Three types of RNA viruses
Positive stranded, negative stranded, retroviruses. If positive, similar to RNA, if negative, transcription must occur first.
RNA is first transcribed to DNA. Transcription, translation, and replication often occur in the cytoplasm.
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.
Primarily affects young children, causing upper and lower respiratory tract infections like croup, common cold, bronchiolitis, pneumonia
Causes croup along with HPIV2, both occur in fall
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
Nucleoside analog that inhibits nucleic acid synthesis
Monoclonal antibody against F protein, used for high risk infants
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.
Enveloped, single stranded positive sense RNA, glycoproteins form halo-like projections around surrounding envelope. RNa genome plus N protein form helical nucleocapsid.
Replication of coronavirus
Virus fuses w/ cell and genome is released in cytoplasm. Translation of the genome occurs in two phases: early phase produces RNA polymerase, late phase negative sense RNA yields structural and nonstructural proteins.
Where does the coronavirus assemble within a cell?
At the rough ER, and is released via exocytosis.
Coronavirus clinical syndromes
Common cold and other respiratory infections, gastroenteritis, SARS
Reservoir of coronavirus
Common in many animal species, generally cause infections in winter and spring.
Respiratory tract secretions through person-person contact or fomites.
PCR of respiratory secretions/stool, antibody assays, electron microscopy
Where does transcription/replication for DNA viruses occur?
In the nucleus, usually more genetically complex then RNA viruses.
Linear double stranded DNA virus, non encapsulated icosadeltahedron, capsid is made of 240 capsomeres consisting of hexons and pentons. 12 pentons each have a base and a fiber which contains viral attachment protein
How does adenovirus replicate?
Viral fibers attach to a glycoprotein member of the immunoglobulin superfamily. Penton base interacts with an integrin on host cell which results in endocytosis. DNA genome delivered to the nucleus, transcription of mRNA occurs in two phases.
Where are adenovirus capsid proteins produced?
Cytoplas, and then transported to the nucleus for viral assembly. Virus remains in the cell and is released when the cell degenerates or lyses.
Adenovirus clinical syndromes
URI/LRI, pharyngo-conjuctivitis, gastroenteritis, hemorrhagic cystitis
Where does adenovirus persist?
In lymphoid tissue, can lead to viremia
Cytosine analog that serves as a substrate and inhibits viral DNA synthesis. Nephotoxic, requires IV administration.
Causes common cold, pharyngitis, otitis media