Respiratory Viruses and Atypical Respiratory Pathogens Flashcards
Name the types of respiratory infections
Surface: local spread
- Short incubation, e.g. common cold, Candida
Systemic: spreads from mucosal site of entry to other site in the body
- returns to surface for final shedding stage
- longer incubation- weeks
- e.g. measles, mumps, rubella
Name the types of respiratory pathogens
Professional invaders:- infect healthy respiratory tract
Secondary invaders: - infect compromised tract
What causes infections of the nasopharynx (rhinitis and sinusitis - the common cold)?
Various viruses
Transmission by aerosol
Self-limiting and not systemic in healthy people
No need for identification unless LRT spread
How does the virus infect the nasopharynx?
Adheres to ciliated epithelium
Enters cells, spreading to neighbouring areas
Inflam response = cold symptoms
Adenovirus features?
Icosohedral symmetry, non-enveloped resistant to desiccation
Attach via adhesions on the end of penton fibres
dsDNA
Cause pharyngitis: conjunctivitis, bronchitis
What is pharyngitis and tonsilitis?
Complication of colds due to surrounding infecs
Site of entry of EBV (Herpes) and mumps virus
70% caused by viruses - rhinoviruses, adenoviruses, influenza viruses
Mumps features?
Paramyxovirus
Air-borne spread
Common in school age children - most vaccinated (MMR)
Complications - Orchitis = inflam of testicles
What causes laryngitis and tracheitis?
Features?
Parainfluenza viruses, adenovirus and influenza
Burning pain in larynx and trachea, easily obstructed in children
Cough with stridor inhalation
Causes of bronchitis and bronchioitis?
Viral causes - rhinoviruses, coronaviruses, adenoviruses, influenza
Atypical pathogens - mycoplasma pneumoniae
Many 2ndry infecs - especially in children - narrow airways - leading to bronchiolitis and pneumonia
What causes 75% of bronchiolitis?
Respiratory syncytial virus
RSV (Resp syncytial virus) features?
Aerosol and surface transmission
Pathology creates large fused cells
Outbreaks in winter
Nearly all children infected by 2yrs old but only as common cold
Severe in young infants - peak mortality 3 months of age
Infants - coughs, cyanosis, rapid resp rate, pneumonia and bronchiolitis
Older = more like common cold
Treatment of RSV?
Supportive
Hydration
Bronchodilators
Severe cases require ribavirin antiviral or palivizumab-prophylactic
Name the influenza virus?
Orthomyxoviridae
How does orthomyxoviridae cause influenza?
Transmitted by aerosol droplet
Restricted to coldest months of the year
Initial infec: virus attaches to sialic acid receptors on epithelial cells via viral HA protein
1-3 days: liberated cytokines result in systemic chills, malaise, fever, muscle aches, runny nose and cough
Recover after 1 week but some get pneumonia and bronchitis
2ndry invaders = lethal infections: pneumococci, staphylococci
Describe the structure of the influenza virus?
2 surface glycoproteins: - HA - Haemagglutinin - NA - Neuraminadase Host derived viral envelope ssRNA genome: 8 segments Nucleoprotein and polymerases
What do the major antigens of the influenza virus do?
HA: major antigenic determinant:
- HA binds sialic acid receptors on epithelial cell surface
- Major source of antigenic variation
NA: second antigen determinant:
- Involved in release of the virus from host cells during budding
Name the types of influenza?
A - Yearly epidemics and occasional worldwide epidemics - animal reservoir
B - Yrly epidemics - no animal reservoir
C - Minro respiratory illness - no epidemics
How to classify influenza?
Influenza type, location of isolation, strain number, yr of isolation, antigen
H-antigens (HA)
- 16 types but only 3 human adapted (H1-3)
N-antigens (NA)
- 9 serotypes but only 2 are human adapted (N1-2)
How does the viral uptake of HA occur?
- HA mediates binding to sialic acid containing receptors
- Internalised by endocytosis
- Endosome acidified- HA conformation alters, M2 ion channel important here
- HA mediates fusion of viral envelope and endosome membrane
Viral RNA and polymerases delivered into the cell
REPLICATION
What causes antigenic DRIFT?
Small point mutations in HA and NA that accumulate = new variant viruses that can re-infec individuals
Source of yrly flu epidemics
All types of influenza
Antigenic SHIFT features?
Cause major shift in viral composition
Major gene reassortment = new HA and NA types formed
Cause of major world pandemics
Only influenza A
How does antigenic shift occur?
Simultaneous infection of human/ animal with Human and ‘other’ influenza virus
Reassortment of genes due to homologous recombination with existing human virus
Dissemination through immunologically naïve population
WORLDWIDE PANDEMIC
Where did HINI swine flue come from?
Re-assortment of existing swine flu viruses
Contain genes of Human, Swine and Avian origin
Amantidine resistant and some oseltamivir resistant
VACCINE has been widely distributed globally
What is the global action plan for influenza?
Increase in seasonal vaccine use
Increase in vaccine production capacity
Research and development
How to combat a pandemic?
Vaccines
Antiviral drugs:
- Resistance a problem - tamiflu, relenza
What causes pneumonia?
Organisms less than 5mm enter the alveoli
Often 2ndry to preceding damage - CF or influenza
Influenced by immunocompromisation e.g HIV
Children:
- Viral causes - RSV, parainfluenza
- 2ndry bacterial infections
Adults:
- Bacterial causes more common - strep. pneumoniae
Viral causes of pneumonia?
Influenza A/B Parainfluenza Measles Resp syncytial virus Adenovirus
What do atypical resp pathogens: atypical pneumonia cause?
Chest pain, cough, SOB
Examples of atypical resp pathogens that cause atypical pneumonia?
Mycoplasma pneumoniae
Chlamydophila
Legionella pneumophila
Mycoplasma pneumoniae features?
Small bacterium with minimalist genome (0.5Mbp)
No peptidoglycan- cholesterol- penicillin resistant
‘walking’ pneumonia- sick but not hospitalised
Major cause of pnuemonia in young adults and students
Efficient binding to cilial epithelial cells via a special cytadherence organelle rich in a cytadhesin (P1) for sialic acid rich glycolipids.
Chlamydophila pneumoniae features?
Small, obligate Gram-negative intracellular pathogen
Complex life-cycle:
- Elementary body- akin to a spore
- Reticulate body- intracellular growth and replication
No peptidoglycan (Pen
Flu-like illness
Detection by ELISA or MicroImmunofluorescence
Legionnaires disease caused by?
Legionella pneumophila
No human-human transmission
Acquired form environmentally derived aerosols
Aircon, heating, showers
Common in hospital, high rise blocks, hotels, student accom
Causes confusion and pneumonia symptoms
Intracellular invasion of lung cells and phagosomes
Legionella pneumophila features?
Motile aerobic Gram-negative rod
Isolation on BCYE medium (Buffered Charcoal Yeast Extract)
Urinary antigen test
Rhinovirus attachment mechanism?
Caspid protein binds to ICAM-1 type molecule on a cell = common cold
