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Flashcards in Respiratory Viruses Deck (67)
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Viruses Covered

Respiratory Syncytial Virus

Parainfluenza Virus Types 1, 2, 3, 4,





Human Metapneumovirus


Respiratory Tract Disease

More episodes of illness than any other organ system
- 75-80% of all acute morbidity and visits to physicians
- respiratory tract is main portal of entry for many organisms, so not surprising that it is the most common site of infection by microbial pathogens as in direct contact with the physical environment
- wide range of organisms can infect the respiratory tract, including viruses, bacteria, fungi and parasites

Upper respiratory tract
- colds

Lower respiratory tract
- 4th most common cause of death in developed countries


Global Burden of Respiratory Disease

Public health issue!
Leading killer of children < 5 yrs old , especially RSV

Pediatric ALRI < 5 yrs old
RIV> Influenza> Pneumococcal > HiB


Acute viral respiratory disease

Viruses account 80% or more of RTI's

All age groups

3 - 4 viral illnesses per year per person, mostly in young children!

Abx have no effect but 60% get them!


Who is at greatest risk for acute viral respiratory disease?

The very young

The elderly

Chronically ill



Viral respiratory illness

Children vs Adults

Children: implicated in 40-70% CAP, >90% of bronchiolitis, over 90% asthma exacerbation

Adults: 30-50% of cap, > 80% asthma exacerbation, 20-60% exacerbation of COPD

**infection messes with your epithelial cells so you are predisposed to secondary bacterial infections in respiratory tract and can affect other organ systems**


Location in Respiratory Tract - relates specific site of infection to various symptoms

Where do most infections occur?

Most infections are limited to upper airways

LRTIs common in defined populations

Cough, runny nose, sneezing, sore throat, ear pain, congestion

Systemic manifestations of fever, headache, chills malaise, myalgia also common

Last 7-10 days in most, 2 - 3 weeks in many, longer in some


Common cold




Laryngotracheobronchitis in infants (croup))



Common cold: nasal obstruction, nasal discharge

Pharyngitis: sore throat, red throat with or without exudate

Pneumonia: cough, chest pain, rales

Laryngitis: hoarseness

Laryngotracheobronchitis in infants (croup)): hoarseness, barking cough, stridor

Tracheobronchitis: nonproductive cough, substernal pain

Bronchioliti: cough, dyspnea, wheezing


Common complications of viral infections

Secondary bacterial infections causing otitis media, sinusitis, pneumonia


Diagnosis of respiratory viruses

- clinical and epidemiological findings

Virus isolation in cell culture (time consuming, labor intensive and costly and not all respiratory viruses grow in culture): used to be gold standard but not anymore

Rapid antigen test
- cheap easy but poor predictive value outside of peak season
- IFA and EIA
- not as sensitive as cell culture

Detection of nucleic acids
- can test many viruses at the same time
- PCR, feasible and most sensitivity **GOLD STANDARD**

Serology- retrospective, seldom done in clinical setting


Specimen collection for detection of respiratory viruses

- close to clinical onset!
- nasopharyngeal aspirates, washes, swabs in VTM, throat swabs in VTM
- nasopharyngeal aspirates or nasal washes are good in young children
- combined thorat and nasopharyngeal swabs are more practical for older children and adults
- children shed virus at higher titers for longer periods of time than adults, upper airway specimens not always best for adults


Why test respiratory viruses?

Infection control

Individual patient management
- help manage special populations
- limit abx, lab tests, hospital procedures
- reduce sequellae

- rapid outbreak identification!


Virus SEasonality at CHOP

Rhinovirus > RSV> adenovirus> influenza A> HMPV> HPV 3 etc


Flu Season is more than just flu

Even during peak influenza season (DEc-Feb)--> see RSV and HMPV at high levels

Incidence highest in winter and lowest in Sumer for respiratory viruses

BUT adenoviruses and rhinoviruses are endemic in the US and seen all year round

Also tropical and semitropical areas dont have same seasonality


Many different respiratory viruses

Heterogeneous group, a real mixed bag
Over 200 distinct viruses belonging to 6 major families can infect human respiratory tract

- some viruses common and well established and you should recognize by name, some are newly identified and significance is still being established

- differ due to size, symmetric, nucleic acid type, lability, mode of replication, and pathogenic and epidemiological behavior


Common respiratory viruses characteristics


Short incubation (1 - 4 days)

Person to person spread

Similar pathogenesis

Increased risk of bacterial superinfection

Immunity imperfect-> reinfection common


Respiratory Virus Transmission

Person to person normally!

Super contagious

Direct contact, aerosolization of infective droplets during coughing and sneezing or indirectly by hand transfer of contaminated secretions or from contaminated objects to nasal or conjunctival epithelium

Eg RSV stable 3 - 30 hours on countertops

Eyes and nose major portals of entry



RV pathogenesis

Viruses enter via nose and eyes

--> infect ciliated respiratory epithelial cell slining upper and lower airways, multiply locally no systemic infection

--> cytolytic causing cell damage and death--> clearance mechanisms compromised (damage creates susceptibility to bacterial superinfections)

--> local and circulating Ab response and T cell recognition with release of cytokines

--> recruitment of neutrophils, NK cells, CD4+ and CD8+ T cells, macrophages, mononuclear cells, eosinophils

--> viruses have ways of evading the immune system

--> certain viruses interact with the immune system to promote immediate hypersensitivity reactions leading to virus-induced wheezing and asthma - CYTOKINE STORM


Cytokine storm

Immune mediated injury caused by immediate hypersensitivity reaction to virus


Respiratory Syncytial Virus (RSV) - who does it affect

Most common cause of bronchiolitis and pneumonia in infants and young children <1 yo

Most important agent of respiratory disease in infancy

Infects virtually everyone by 2 - 3 years of age and reinfections are common throughout life


RSV function and structure

Paramyxovirus family

Enveloped: single stranded RNA

120-300 nm

G and F proteins (surface glycoproteins mediate attachment of the virus to the host cell and fusion, respectively)
- F protein also mediates syncytium formation

Virus contains an RNA dependent RNA polymerase for transcription and replication

Other paramyxoviruses = measles, human parainfluenza, mumps, metapneumovirus

Two subgroups - antigenic types A and B

Significance of variants unknown


What proteins mediate RSV attachment, and fusion to host cell and synctitium formation?

G (attach)

F(form and syncytium)


Antigenic Subgroups of RSV

A - associated with more severe
B - less severe

Significance of variants is unknown


RSV epidemiology


Source of infection?

Who is infected?



Humans= only source of infections

Annual community outbreaks

50% of all families with children

Circulation is effeicient (2/3 of infants infected in 1st yr, all children by 2 - 3 yr)

Age peak of 2 - 5 mo

50% children have 2 + episodes, 40% infx produce lower respiratory tract diseases

Re infx common for all age groups, immunity imperfect and not completely cross protective against two strains


Serious RSV illness

Very young infants, premature infants

Children <2 - 3 yo


Children and adults with chronic illness and compromised immune systems

Mortality = .5-1% but > 15% in impaired host


What is the single most important agent in respiratory disease in infancy?

Leading cause of lower respiratory illness in infants and young children worldwide?



RSV mortality

Leading viral cause of mortality in infancy

10x morality of influenza in infants < 1 yr

500 deaths per year
- 80% in infants < 1 yo


Syndromes of RSV infections in children

Bronchiolitis (most common)





(Ascending--> descending, most common--> leas common)


Clinical Presentation of RSV disease



Clinical findings?


Duration of illness?

URI = cough, rhinitis pharyngitis, fever

LRI = expiration wheezing, air trapping, tachpnea, dyspnea, rales (clicking rattling in lungs), rhonchi (snoring sound in lungs), retractions (sinking in of the chest wall above collarbone, between ribs and below rib cage), nasal flaring, grunting hypoxemia (low oxygenation of blood), irritability, dehydration, respiratory distress

Clinical findings: Hyperexpansion of lungs and hypercapnia (carbon dioxide retention- especially bad when young)

Other; otitis media, vomiting, conjunctivitis

Duration: 10 - 14 days



Look at pic slide 26 of respiratory lecture

- see child with suprasternal and intercostal retractions and nasal flaring--> child cant breathe