Respiratory Viruses Flashcards
What is an URTI?
Upper respiratory tract infections (URTI)
Acute infection involving nose, paranasal sinuses pharynx & larynx
What is an LRTI?
Lower respiratory tract infection (LRTI)
Acute infection involving the airways and lungs
What region is infected in Rhinitis?
Nose
What are the symptoms of Rhinitis?
Sneeze
Watery/purulent discharge
Nasal obstruction
What region is infected in Pharyngitis?
Pharynx
What are the symptoms of Pharyngitis?
Pharyngeal inflammation
Red throat and or exudates
What region is infected in Croup?
Subglottic trachea
What are the symptoms of Croup?
Hoarseness
Barking cough
Inspiratory stridor
What region is infected in tracheobronchitis?
Trachea and larger bronchi
What are the symptoms of tracheobronchitis?
Cough, coarse rhonchi, mucus hyper-secretion
What region is infected in bronchiolitis?
Small bronchi and bronchioles
What are the symptoms of bronchiolitis?
Tachypnea, wheezing, hyper-resonance to percussion
What region is infected in viral pneumonia?
Lungs, especially alveoli
What are the symptoms of viral pneumonia?
Cough, fatigue, fever, shortness of breath, chest pain
What are the common causes of the common cold?
Rhinoviruses
Coronaviruses
What are the less common causes of the common cold?
Influenza viruses Parainfluenza viruses Enteroviruses Adenoviruses RSV
What is the common cause of croup?
Parainfluenza viruses
What are the less common causes of croup?
Influenza viruses
RSV
What is the common cause of bronchiolitis?
RSV
What are the less common causes of bronchiolitis?
Influenza viruses
Parainfluenza viruses
Adenoviruses
Rhinoviruses
What is the common cause of influenza-like illness?
Influenza viruses
What are the less common causes of influenza-like illness?
Parainfluenza viruses
Adenoviruses
What are the common causes of viral pneumonia?
Influenza viruses
RSV
Adenoviruses
What are the less common causes of viral pneumonia?
Parainfluenza viruses
Enteroviruses
Rhinoviruses
Coronaviruses
When do RTIs usually occur?
RTIs occur typically late autumn to end winter
Peaks may vary for particular viruses
Why do RTIs peak in autumn/winter?
Drop in temperature Rise in humidity Re-opening of schools Emotional depression (SAD) Increased indoor activities
What are the main vectors for RTIs?
School children
Describe the pathogenesis of an RTI
Virus enters Respiratory Tract
Absorption to ciliated epithelium via specific receptor
Viral replication
Hit and Run strategy
Host defences activated
high levels interferon α, IL–2, IL-6, and (TNF)-α
Possible secondary bacterial infection
NK cells and Macrophages activated
Fever and systemic symptoms
Recovery & cytotoxic T cell/antibody production
What family do the Human Parainfluenza Viruses (HPIV) belong to?
Paramyxoviridae
What are the two genera of HPIV?
Respirovirus (serotypes HPIV-1 and HPIV-3)
Rubulavirus (serotypes HPIV-2 and HPIV-4a and b)
Which serotype of HPIV is the most severe (esp. in young children)?
HPIV-3
Describe the disease spectrum for HPIV
Subclinical to respiratory collapse
How long is the incubation period for HPIV?
2-4 days
Why is the incubation period so short?
The disease is found where it infects, so the virus does not need to spread through the body to cause symptoms
What does HPIV-1 and 2 cause?
Croup in very young, and milder RTIs
75% infected by age 5
What does HPIV-3 cause?
Severe bronchiolitis & pneumonia /severe croup
80% infected by age 4
What does HPIV-4 cause?
Mild URT infection
How long is the shedding period for HPIV?
3-10 days
How is HPIV transmitted?
Transmission via direct inoculation or large particle aerosols
Does reinfection occur with HPIV?
Yes, reinfection common (with reduced disease), esp. with URTI
Describe the epidemiology of HPIV
HPIV-1 biennial /autumn
HPIV-2 biennial/autumn
HPIV-3 annual/spring
HPIV-4 less well characterised
What are the risk factors for HPIV?
Malnutrition Overcrowding Vitamin A deficiency Lack of breastfeeding Smoking
What family does Respiratory Syncytial Virus (RSV) belong to?
Paramyxoviridae
What are the genera of RSV?
Pneumovirus - subtypes A and B
How is RSV transmitted?
Hands and fomites>droplets
Describe the epidemiology of RSV
Peaks between December and March
Annual epidemics November to April
Describe the disease spectrum of RSV
Mild cold to bronchiolitis
Most common viral LRTI in very young & elderly
Rare in neonates
What are the risk factors for RSV bronchiolitis?
Incidence highest in urban areas Premature birth, low birth weight congenital heart disease, CF, IS Lower socioeconomic status Being male > 2 smokers in household > 5 people in household Elderly and transplant patients
Describe the immunopathogenesis for RSV bronchiolitis?
RSV is not cytopathic. Immune response to RSV infection results inepithelial damage and cellular desquamation.
Inflammatory changes in the lung cause narrowing of airway producing clinical symptoms of bronchiolitis
RSV can also cause asthma exacerbations in older children
What family does Human Metapneumovirus (hMPV) belong to?
Paramyxoviridae
Describe the disease spectrum of hMPV
URTI and LRTI very similar to RSV, less severe
Immunocompromised > risk severe disease
Seroprevalence 100% by 5 years
Recurrent infections throughout life
Describe the epidemiology of hMPV
Annual epidemics late winter, early spring
Coincides/overlaps with RSV season
Sporadic infection year round
What is the method of transmission for hMPV?
Direct /close contact with respiratory secretions
How is adenovirus characterised?
Direct /close contact with respiratory secretions
Describe the features of adenoviruses
Double stranded DNA
80nm, non-enveloped icosahedron
Fibre projecting from 12 vertices
2 Antigens: Group common & Type specific
How many serotypes of human adenovirus are there?
> 51
What family does Rhinovirus belong to?
Picornaviridae
Describe the features of rhinovirus
18-30nm, non-enveloped, icosahedral, +ssRNA
Optimal growth 33˚C, acid labile
Causes 40% URTI.
Droplet transmission
Epidemiology- peaks late spring & autumn
2-3 day incubation, URTI 7days, virus shedding for 3 weeks
LRTI more common in children
How many serotypes of Rhinovirus are there?
> 100
Describe the features of Coronaviruses
80-200nm diameter
+ ssRNA
Envelope has 3 major glycoproteins:
S – Spike , E – Envelope, M - Membrane
Adult infection less common.
Can cause:
- URTI Causes 2-10% common colds
- Mild, self-limiting disease
- Enteric – typically in infants
What is the incubation period for Coronaviruses?
3 days
Which Coronaviruses have been identified as causing disease in humans?
Alpha coronaviruses 229E and NL63
Beta coronaviruses OC43
What are the clinical features of SARS-CoV?
Fever >38 °C & myalgia
20% progressed to ARDS
30% mortality
How is SARS-CoV transmitted?
Transmission by droplet & faecal contamination
What is the natural reservoir for SARS-CoV?
Chinese horseshoe bat
What is the intermediate (amplification) host for SARS-CoV?
Masked palm civet cat
Describe the features of MERS-CoV
Novel Coronavirus identified June 2012 in Qatari national who died from severe
respiratory infection and renal failure
As of 2016, 1638 laboratory-confirmed cases reported with 587deaths
Family cluster in UK provides 1st evidence of human-to-human transmission
Zoonoses -originated in bats, transmitted to camels sometime in the distant past
Camels major reservoir for transmission to humans
Currently limited human – human transmission
Uses different cell receptor to SARS.
What cell receptors does SARS-CoV use?
ACE2 in LRT
What cell receptors does MERS-CoV use?
Dipeptidyl peptidase 4 (DPP4 or CD26) in URT and LRT
What are the different techniques used to diagnose RTIs in the lab?
Cell culture
Immunofluorescence
Serology
PCR
How is cell culture used to diagnose RTIs?
Infection induces typical cytopathic effect which can be seen under a microscope
e.g Parainfluenza viruses form large multinucleate syncytia
How is immunofluorescence used to diagnose RTIs?
IF of viral antigen in cells from nasopharyngeal washes/cell culture isolates
How is serology used to diagnose RTIs?
Complement fixation test
ELISA tests –specific IgG & IgM
Why is PCR usually used to diagnose RTIs?
Applicable to RNA or DNA viruses Rapid Multiplex PCR Products can be sequenced Improved patient management and disease surveillance
How are RTIs prevented and treated?
Strict infection control
Supportive intervention
Stop antibacterial therapy
Children with Severe Viral Respiratory Disease
- May use oxygen therapy / mechanical ventilation
- For RSV, HPIV, hMPV Ribavirin aerosol may be used
- For RSV administer Palivizumab monoclonal antibody
