Micro - Paramyxoviruses (RSV, hPIV, hMPV) Flashcards
RSV, hPIV, hMPV are (enveloped, nonenveloped) (segmented, nonsegmented) (RNA+, RNA-, DNA)
Enveloped nonsegmented RNA-
What distinguishes paramyxoviruses from influenza?
They are nonsegmented so antigenicity doesn’t change much unlike the segmented influenza virus
RSV is the leading cause of:
Viral LRI in infants
hMPV is the second leading cause of:
LRI in kids (behind RSV)
What can hMPV cause in older children and adults?
ARDS
Cause of croup? Another name for croup?
hPIV1-3
Laryngotracheobronchitis
What faction of the adult population is susceptible to hPIV infection?
Elderly
Immunocompromised
What are the two most important distinguishing factors of an RSV/hPIV/hMPV infection?
Age and seasonality
When is RSV most common in Memphis?
Oct-Mar
At what age is RSV infection most common?
2-8
When is hMPV most common?
Winter-spring
Most kids have been infected by hMPV by age ___ and seroconversion rates for hMPV ~ 100% by age ___
3
10
When is each strain of hPIV1-4 most common?
hPIV1 = autumn of odd # years (biennial) hPIV2 = follows hPIV1 outbreak hPIV3 = spring and summer hPIV4 = sporadic
Where do the paramyxoviruses replicate?
CYTOPLASM***
Describe the entry of paramyxoviruses
Receptor binding protein and fusion protein mediate fusion of viral envelope with membrane of host cell
What other function besides entry does fusion protein mediate?
Fusion of infected cell with adjacent cell = forms SYNCYTIUM*****
Tropism of paramyxoviruses?
URT and LRT only; do NOT cause systemic infection
Why don’t paramyxoviruses cause systemic infection?
hPIV and hMPV use their HN protein to bind to sialic acid, which is found in the mucus membrane layer lining respiratory epithelium.
Less is known about HSV binding protein, so it’s just called G (for glycoprotein) and it binds nucleolin, found on all cells, and GAGs of the respiratory epithelium
Attachment of hPIV/hMPV vs. RSV
RSV does NOT bind sialic acid
Two major envelope proteins of RSV
G & F (fusion protein)
Two major envelope proteins of hMPV and hPIV
F & HN (hemagglutinin, neuraminidase)
Characteristic feature of paramyxoviruses
Syncytia formation (due to F protein)
Two primary cell types targeted by RSV
Airway epithelial cells and dendritic cells
Progression of RSV,hPIV,hMPV pathogenesis
Infects URT epithelial cells then moves to the LRT via dendritic cells &/or cell-to-cell transfer
6 key pathological findings of RSV,hPIV,hMPV infection
Airway inflammation Necrosis Sloughing of airway epithelial cells Edema Excessive mucus production Interstitial infiltrates
What would you expect to see on CXR of pt with RSV infection?
Hyperinflation
Increased interstitial markings
Atelectasis (sometimes)
Pulmonary infiltrates (sometimes)
What is croup? Characteristic sx?
Laryngotracheobronchitis = edema of the mucus layer and swelling due to hPIV1-4 infection
Barking cough with inspiratory stridor
1 cause of bronciolitis and pneumonia in infants < 1 yo
RSV
Where does RSV initially infect? Possible chronic complication?
Nasopharynx
Damage to lung can become permanent and result in chronic lung disease like asthma
Sx progression in RSV infection
1-3 days after infection = cough, low-grade fever, wheezing (URI sx)
2 days later = tachypnea, polyphonic wheezing, retractions, rales, cyanosis, hypoxemia (LRI sx)
RSV sx in adult
Rhinorrhea Cough HA Fever Fatigue
High risk factors for developing severe RSV infx
Prematurity Infected before 3 months of age Chronic lung disease Congenital heart problem SCID O2 sat < 95% RR > 70 Atelectasis Pneumonitis Toxic appearance on presentation Neuromuscular disease
Most common presentation of hMPV infection
Bronchiolitis +/- pneumonia
Who is most susceptible to a severe hMPV infection?
Infants < 1 yo
Elderly
Pt on immunosuppressants
hPIV is second only to HSV as cause of:
Bronchiolitis and pneumonia in infants and young children
What other infection is common with RSV and hMPV?
Otitis media (think S. pneumoniae)
Sx of hMPV infection?
HIGH fever Rhinorrhea Tachypnea Dyspnea Wheezing
Sx of hPIV infection?
Pharyngeal erythema Nonproductive to minimally productive cough Nasal congestion Fever Cough that develops into croup Hoarseness (inflammation of vocal cords)
How are the paramyxoviruses transmitted?
Person-to-person via large droplets
What is special about the epidemiology of RSV?
It is the most predictable epidemic disease in the US
occurs Oct-Mar
Which causes more widespread illness: RSV or influenza?
Influenza (RSV emerges only within a community)
~100% seroconversion of RSV by age ___; ~100% seroconversion of hMPV by age ___
3
10
RSV sx vs. common cold sx
RSV is more severe
(T/F): Most people only get infected with a paramyxovirus once
False; reinfection occurs throughout life
High risk factors for acquiring RSV
Young kid in daycare Older sibling in daycare Crowding Low SES Multiple birth sets (especially triplets+) Minimal breastfeeding Exposure to pollutants (smoking)
Primary RSV infection vs. recurrent RSV infection
Recurrent more likely to be confined to URT
also, RSV infection with increasing age likely to be restricted to URT
When are you most likely to see croup?
Autumn of odd numbered years
Diagnostic options for RSV
- Culture from nasal secretions
- ELISA for antigen
- RT-PCR
Gold standard for diagnosing hMPV
RT-PCR (most sensitive test)
Although diagnostic assays are generally not used for hPIV, what could be used?
High IgM/IgG titer
RT-PCR
Culture
Immunoassay
Why isn’t serological testing commonly done is paramyxovirus suspected?
Seroconversion is almost universal
Which paramyxovirus has a vaccine?
None
Tx of paramyxovirus infection is mainly:
Supportive
Goals of supportive tx for paramyxovirus infection?
Oxygenation, hydration, nutrition
Give some examples of supportive tx used for paramyxovirus infection
Bronchodilator O2 Ventilation Fluids Aerosolized epi
Two Rx used for RSV and their MOA
- Palvizumab - mab that neutralizes RSV
2. Ribavirin - nucleoside analog that prevents replication
AE of ribavirin
Teratogen
Indication for palvizumab vs. ribavirin
Palvizumab - premies, high risk pt < 6 months
Ribavirin - pts on immunosuppresant
