MedicalVirology Lower Respiratory TractInfections Dr. Sameer Naji, MB, BCh, PhD(UK) DeanAssistant Head of Basic Medical SciencesDept. Faculty of Medicine The HashemiteUniversity
Viral Lower Respiratory TractInfections Additions are in Italic Green
Structures of the Lower RespiratorySystem • Components of the lower respiratorysystem • Larynx • Trachea • Bronchi • Alveoli • Diaphragm • Various protectivecomponents • Ciliated mucous membrane, alveolarmacrophages, and secretoryantibodies(IgA)
Important Viral Causes of Lower RespiratoryInfections • Influenza(by dr. ashraf) • Para-influenza • Respiratory syncytialvirus • SARS • MERS • Human metapneumovirus (2001)common • in comprised children and elderlypersons • No etiologic agent found(33%)
Para influenzaViruses • It causes Croup(Acute Laryngotracheobronchitis/ Laryngotrachiaites (the lung is involved))and pneumonia inchildren • Common cold – like disease inadultsand children. • 5 subtypes: 1, 2, 3(most important)4a and4b • Surface spikes consist of H(hemagglutinin), N(neuroaminidase)and fusionproteins. H andNonthesamespikewhilefusionproteinisona differentspike.
Epidemiology • Transmission: respiratory droplets,winter months.(viruses have seasonal variations) • Croupisthecommonestclinicalmanifestationof parainfluenza virus infection, caused bysubtypes 1 and2. • It occurs in children (below 3years). • Parainfluenza 3is prone to producebronchiolitis andpneumonia(so it causes infection in more lower areas of the respiratory tract) . • The majority of infections withparainfluenza viruses aresubclinical.
ClinicalFindings • Croup • Harshcough(larynx is edematous) • Inspiratorystridor(hardly breathing) • Hoarsevoice(because of edema ) • SO CROUP IS AN EMERGENCY CASE – send your patient to hospital • Patients are usuallyafebrile. • About 80% of patients exhibit runny nose(called coriza)1 to 3 days before the onset of the cough(it can be messed with common cold). Usually, respiratorysymptomssubsidewithin1or2days.
Inadditiontocroup,parainfluenzavirusescause • commoncold, • pharyngitis, • otitismedia, • bronchitis • pneumonia. • Othervirusescaninducecroup,suchasinfluenza viruses, RSV, measles andchickenpox. • Parainfluenzavirusinfectionsinadultsarerelatively uncommon,andsymptomsareusuallylessseverein adults thanchildren.
LaboratoryDiagnosis • Croupisawell-defined,easilyrecognizedclinical entity.(if you face a patient with croup outside your clinic, let him breathe a moistened air) • Cell cultureisolation • Immunoflurescence(antigen-antibody reaction – needs UV microscope) • Antibody rising titre using HAI orELISA(there should be 4x increase in titre)
Treatment • Hospitaladmission • Nursing in plastic tents supplied withcool, moistenedoxygen(first step in treatment) • Severe respiratory obstruction may require endotracheal intubation followed by atracheotomy.
Respiratory Syncytial VirusInfection • RSV causes Pneumonia and bronchiolitis ininfants • (infant<1 year; neonate< 28 days) • (baby<7 months can have pneumonia associated with chlamydiatrachomatis) • Fusion protein causes cellsto fuse, forming multinucleated giant cells(syncytia) • RSV causes outbreaks of respiratoryinfections • everywinter. • RSV is a majornosocomial pathogenin pediatricwards(because it’s a droplet infection). • The pathogen may be introduced by infected infantswhoareadmittedfromtheoutsideand adults, especially members of staff with mild infections.
Transmission • Respiratorydropletsanddirectcontactof contaminatedhandswiththenoseoreye • The incubation period is usually 3 - 6days(in parainfluenza 1 to 2 or 3 days) • The virus spreads along the epithelium of the respiratory tract, mostly by cell-to-celltransfer • Pathogenesis • Viruscausessyncytiatoforminthelungs • ImmuneresponsetoRSVfurtherdamagesthelungs
CLINICALFINDINGS • RSV is the most common cause of severe lower respiratory disease in young infants. It isresponsible for 50 - 90% of cases of bronchiolitis, 5 - 40% of pneumonias and bronchitis and less than 10% of croups in youngchildren. • Youngchildren • otitismedia • Older children &adults • common cold like –disease • Infants • FebrileURTI • Lower respiratory tractinvolvement • Worseningcough • Tachypnoea (fast breathing) anddyspnoea • Inbronchiolitis,therespiratoryratemaybeelevated, with wheezing and hyperinflation. Cyanosis may be present in severecases(because of tachypnoea ).
Risk groups forfatal RSVinfection • Infants with congenital heartdisease • Infants with underlying pulmonarydisease • especially bronchopulmonarydysplasia • Immunocompromizedinfants • childrenwhoareimmunosuppressedorhavea congenital immunodeficiencydisease. • Nephrotic syndrome(kidney leaking protiens)and cysticfibrosis(a genetic disease – prone to bacterial infection with the mucoid type pseudomonas aeruginosa)
Complications • Apnea((توقف التنفس • occurs in approximately 20% of cases(premature infants). The apnea is non-obstructiveand develops at the onset or within the first few days ofillness. • The most common complication is prolonged alterations in pulmonary function, whichmay lead to chronic lung disease in laterlife.
LABORATORYDIAGNOSIS • Immunoflurescenceon smears of respiratory secretions • ELISA for detectionof RSVantigens • Isolation in cell culture (multinucleatedgiant cells orsyncytia) • Rise of antibodytiter.(4x)
A syncytium forms when RSV triggers infected cells to fuse with uninfectedcells
Treatment • All infants with RSV lower respiratory tract disease are hypoxemic and oxygen shouldbe given to hospitalizedinfants • Aerosolized ribavirin in severely illinfants • RespiGam contains a high concentration of protective antibodies against RSV. It is given for the prevention in children under24months withbronchopulmonarydysplasiaorahistoryof prematurebirth.