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Medicine 2 - 03 Pneumonia > 7 Respiratory Tract Infections: Viral infections > Flashcards

7 Respiratory Tract Infections: Viral infections Flashcards

1
Q

Describe upper respiratory tract infections (URTIs)

And also state what the names are of infections of different parts of the upper respiratory tract

A
  • Anything above the trachea
  • Common (like Cold), often mild (can vary)
  • Often viral in aetiology (cause)
  • Damage from viral infection - can lead to further bacterial/fungal infections
  • Not many treatments - the key is prevention
Nose = rhinits
Throat = pharyngitis
Sinus = sinusitis
Ear = otitis media, otitis externa
Epiglottis = epiglottitis
Larynnx = laryngitis
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2
Q

Describe what coryza is

Also, list some causes of it

A

It is also known as the common cold
- It is an acute inflammatory contagious disease in the upper respiratory tract
- It is not clear which virus, but can be:
> Rhinovirus (most common)
> Parainfluenza viruses 1-4
> Coronaviruses (often asymptomatic - young people)
> Adenovirus (50 or so serotypes - the cause of conjunctivitis)
> Enterovirus

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3
Q

What can coryza (common cold) predispose some people to

A
  • Sinutitis
  • Otitis
  • Bronchitis
  • Pneumonia
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4
Q

Describe pharyngitis/tonsilitis

A

Both are very common,

  • but pharyngitis is an infection of the throat
  • and tonsilitis is an infection of tonsils

Causes:

  • Viral: adenovirus, influenza
  • Bacterial: group A streptococcus bacteria
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5
Q

Give some symptoms of pharyngitis/tonsillitis

A
  • Sore throat
  • Difficulty swallowing
  • Fever
  • White pus-filled spots on tonsils
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6
Q

Describe infectious mononucleosis

A

It is also known as glandular fever
- It is an infection of the throat

Diagnosis
- syndromic (not clear); a constellation of signs and symptoms (not autological)

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7
Q

Describe some symptoms and signs of infectious mononucleosis (aka glandular fever)

A

Symptoms:

  • Pharyngitis
  • Lymphadenopathy (cervical generalized)
  • Fever
  • Malaise

Signs:

  • atypical mononuclear cells in peripheral blood (on blood film/smear)
  • CD8 positive T cells - activate + responding to infections
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8
Q

State some causes of infectious mononucleosis (aka glandular fever)

A
  • Epstein-Barr virus (most common)
  • Cytomegalovirus (same family as EBV)
  • Toxoplasmosis (illness that can have other symptoms with muscle pain, fever, tiredness - dangerous in pregnant women as it can affect the foetus)
  • HIV seroconversion (body starts producing detectable HIV antibodies - can occur 4-6 weeks after HIV infection - similar symptoms to glandular fever)
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9
Q

Describe croup

A

It is a childhood condition that affects the trachea, bronchi, and larynx
- occurs in children, during late autumn and early winter months

Viral causes:
- Parainfluenza virus + respiratory syncytial virus

Symptoms:
- Inflammation in throat + epiglottis - gives characteristic ‘barking’ cough (like a seal)
> Inspiratory stridor due to narrowed airways (harsh)

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10
Q

Describe epiglottitis

A

It is inflammation of the epiglottis

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11
Q

Give symptoms of epiglottitis

A
  • In young children: breathing difficulties, stridor + hoarse voice
  • In adults and older children: epiglottis inflamed, swallowing difficulties, and drooling
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12
Q

Give some causes of epiglottitis

A
  • Usually caused by an infection with Haemophilus influenzae type B (HiB) bacteria - now very rare (we vaccinate against this - HiB vaccine)
  • Potentially life-threatening - can cause epiglottitis (fatal if it blocks the airway), meningitis, and septicemia
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13
Q

Give common viral causes of lower respiratory tract infections (LRTI)

A
  • Influenza viruses

- Respiratory syncytial viruses (RSV)

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14
Q

Give some rarer viral causes of lower respiratory tract infections (LRTI)

A
  • Varicella-zoster virus - chicken pocks (in children - itchy, adults - chickenpox, pneumonia - life-threatening)
  • Measles virus (giant cell pneumonia) - rare due to MMR vaccine (complications in px who are immunocompromised - leukaemia - can be fatal)
  • Cytomegalovirus (immunocompromised - virus can be latent)

MERS (and SARS) coronaviruses

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15
Q

Describe the influenza virus

and its basic genomic makeup

A 
Lots of different versions
- Genome of the virus is segmented
 > -ve ssRNA genome
- 8 segments - encode 11 proteins
- Segments 4 + 6 encode for major surface protein

> segment 4 = Haemagglutinin (HA)
segment 6 = Neuraminidase (NA)

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16
Q

Explain the typing system of influnza viruses (A, B, C)

A

Typing is categorized on basis of internal proteins (nucleoproteins + matrix protein)

17
Q

Explain the subtyping system of influenza viruses

A

Only applies to type A
- Defined on basis of surface protein =
> Haemagglutinin and Neuraminidase
- Subtypes numbered (like H1N1 - HA + NA)

So, every time there is an outbreak, it is based on its characteristics

e.g. A/Panama/01/1 (H1N1)
Type/where it was isolated/when it was isolated (year)/unique number for no. of samples

If type A, the subtype is named (H1N1)

18
Q

Describe influenza - the illness

A 
'Flu-like illness' 
2 major components to illness:
- Respiratory tract symptoms
 > rhinitis, cough, shortness of breath
- Systemic symptoms:
 > fever, headache, myalgia (tiredness)

Difference between common cold + influenza
- (no systemic symptoms in the common cold)

19
Q

Describe the pathogenesis of influenza

A
  • Pneumotropic virus i.e. infects cells
    (haemagglutinin surface protein) lining respiratory tract - down to alveoli
  • This infection is lytic (kills cells) - stripping off the respiratory epithelium

The lytic nature of the virus makes the LRT susceptible to inhalation of bacteria
- It removed 2 innate defence mechanisms
> mucus-secreting cells and cilia
- Virus triggers Interferon production - circulates in the blood (not the virus that causes the LRT symptoms)

This contributes to the feeling of illness = systemic symptoms

20
Q

List the complications of influenza

A

Pneumonia:

  • Primary viral pneumonia
  • Secondary bacterial pneumonia
21
Q

Describe the primary viral pneumonia that arises due to influenza

A

Primary viral pneumonia

  • Alveolar walls filled with mononuclear cells infiltrate (inflammatory responses)
  • Air spaces filled with fibrinous exudate composed of fibrinogen and fibrin
22
Q

Describe the secondary bacterial pneumonia that arises due to influenza

A

Secondary bacterial pneumonia

  • More common
  • Air spaces filled with polymorphonuclear leukocytes (inflammatory response to bacterial infections)
23
Q

Describe the cardiovascular complications associated with influenza

A
  • Px with underlying cardiovascular complications most at risk
  • Pathogenesis unclear -
    > could be due to myocarditis - direct spread of the virus into the myocardium
    > could be due to inflammation of lung putting extra strain on right side of heart
    (inflammation of cardiac muscle)
24
Q

Describe nervous complications associated with influenza

A
  • Post-infectious Encephalitis (abhorrent immune response - immune system attacks brain)
  • Rare but serious complications - inflammation of the brain
25
Q

List the high-risk patients with influenza (at-risk groups)

A

Influenza epidemics lead to excess deaths and hospitalizations

Risk groups identified:
- Patients with pre-existing:
 > Lung disease, cardiac disease, endocrine disease, immunodeficiency, liver disease
- Anyone > 65 years old
- Pregnant women (complications)
- Children
26
Q

Describe the epidemiology of influenza

A

Annual winter epidemics are associated with excess deaths, hospitalizations, and other serious consequences (mainly in at-risk groups and the elderly)

  • Unusual, other outbreaks do not occur annually, as after 1-year - there is immunity
  • Whereas with influenza, this is not the case (12-month cycle)

Worldwide pandemics - high mortality

27
Q

Describe how influenza may be able to come back every 1 year - and have worldwide pandemics

A

Antigenic drift + antigenic shift

  • Gradual change in the surface proteins (HA and NA) - these small changes over time leads to antigenic drift
  • Antigenic shift - more dramatic -
    > recombination between different strains (2 different strains entering same organism in same cell at same time, exchanging genetic material as they replication) -
    > leads to major changes in surface proteins (HA and NA) -
    >leads to a different strain virus

Lack of immunity - new strain leads to an outbreak

Large increases in cases + hospitalizations and deaths across the world

28
Q

Explain the concept of antigenic drift (in context to annual influenza epidemics)

A

Antigenic drift

  • Occurs in both influenza A + B viruses
  • (error in replication) - Random spontaneous mutation in viral genes encoding HA + NA -
  • leads to 1-2% amino acid sequence change

But there is a Darwinian selection - whichever stain is more infectious and successful, that one thrives more - passes on its genome

These changes occur in segments 4 + 6, which affect the surface proteins HA + NA
- More effective if they evade vaccine + immune system - more survivability

29
Q

Describe the changes that occur to haemagglutinin and neuraminidase,

and link this to how antigenic drift can lead to annual inlfeunza epidemics

A

On haemagglutinin (What normally happends with vaccines/immunity):

  • Antibodies normally bind to different epitopes (ABCDE) on HA
  • These Ab will neutralise virus, but stopping the HA from binding to receptors on target cell (Ab neutralisation)

So:

  • In these epitopes are where there the mutations are concentration in HA + NA
  • So true Darwinian evolution selected by host immune response,

So, Ab will not affect as well/not at all as previous year’s infection

This accounts for inter-pandemic epidemics (recurrence of infection) - explain annual occurence of influenzas

30
Q

Explain the concept of Antigenic shift, with relation to Influenza pandemics

A

Consider scenario:

  • There are 8 blue segments of RNA - human influenza virus
  • There are 9 purple segments of RNA - avian influenza virus

If they mix at the same time - a new subtype is able to infect humans
- Different mix of strains - new subtype able to infect humans(if changed (purple) strain infects human, the HA and NA surface proteins will be very different - the person has no immunity)

Also, this person is very adapted to replicate inside a human (Very dangerous - can occur naturally)

31
Q

Describe how influenza A reservoirs are formed, and how this leads to new subtypes of the virus are produced

(and relate this back to antigenic shift)

A
  • Wild aquatic shorebirds are the largest + most important reservoir for influenza A
  • Humans and other animals (wild animals, domestic + farmed poultry, pigs, horses cats, seals, mink, whales) can also get affected
  • Pigs support the growth of both human and avian influenza viruses (‘mixing vessels’)
    > Pig have both forms of sialic acid (which is what human and avian influenza bind to) in their respiratory tract, and so susceptible to both strains - so exchange of genetic materials can occur - new stain

Leading to influenza pandemics

Antigenic shift occurs only in influenza viruses
- Genetic reassortment between human and non-human leads to new subtypes
- Leading to 20% new amino acid differences
- Emergence of a new pandemic strain
> population has no existing immunity

32
Q

Give some key measures to combat influenza pandemics

A
  • Infection control - prevent spread (PPE, hand washing, distancing from risk category)
  • Medical treatment - e.g. antiviral drugs, antibiotics
  • Vaccinations (most vulnerable, most likely to spread it) - if the population is more immune - herd immunity + less likely to be transmitted and reducing the chance of mutation + adaptation
33
Q

Describe the Respiratory Syncytial Virus (RSV)

A

It is an enveloped paramyxovirus, -ve ssRNA
- Encodes for 9 polypeptides
> including 2 surface proteins: Fusion (F) and Glycoprotein (G)
- Highly seasonal infection (winter months)
- Extremely common: most children are infected with RSV by 2 years old

34
Q

Describe the disease that RSV can cause:

A
  • Causes LRTI in infants:
    > Bronchitis, pneumonia
  • High hospitalization rates
  • Low mortality (<0.5%)

Requires rapid diagnosis and appropriate infection control measures to prevent the spread
- Can spread in hospital - isolation, RSV wards to prevent deaths in young infants

Undergoes antigenic drift

  • So, reinfection occurs throughout life
  • Presents as URTI in older children and adults (cough/sore throat)
  • Increase in mortality rates in older people

Medicine 2 - 03 Pneumonia (8 decks)

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