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Medical Microbiology > Influenza > Flashcards

Influenza Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What are the features of influenza?

A

Highly infectious acute respiratory disease

Causes regular epidemics

Significant morbidity, mortality and economic loss

Influenza A has cross species transmission and pandemic potential

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2
Q

What are the different types of Influenza?

A

Influenza A
Influenza B
Influenza C

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3
Q

What are the features of Influenza B?

A

Mostly human strains
Common in school outbreaks
Less severe than A
Epidemics occur less often than A

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4
Q

What are the features of Influenza C?

A

Infects Humans and swine (zoonotic)
Different pattern of surface proteins
Mild to no symptoms
By age 15, most have antibodies

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5
Q

What are the different strains of Influenza A?

A

Human
Avian Influenza
Swine flu

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6
Q

How is influenza classified?

A

Classification by surface antigens into subtypes

  • Haemagglutinin (H or HA)
  • Neuraminidase (N or NA)

16 HA and 9 NA for influenza A
- All in aquatic birds

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7
Q

What is the function of Haemagglutinin (HA)?

A

Attachment to infect host cells

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8
Q

What is the function of Neuraminidase (NA)?

A

Removes neuraminic acid from mucin and release from cell

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9
Q

What are the clinical symptoms of Influenza?

A 
Coryza 
Pharyngitis 
Cough
Fever 38 – 40 C
Headache
Anorexia
Malaise, aches & pains
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10
Q

What complications can occur with influenza?

A 
Primary Influenza Pneumonia
Secondary bacterial pneumonia
Cardiac failure
Reyes syndrome
CNS disorders e.g. encephalopathy
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11
Q

Describe the replication cycle of influenza viruses

A

(1) The viral HA binds to sialic acid residues on glycoproteins or glycolipids on the cell surface.
(2) Engulfment of the virus by the cell plasma membrane and formation of an endocytic vesicle.
(3) Delivery of the virus to the endosomal cell compartment.
(4) Fusion of the viral membrane with the membrane of the endosome, induced by the mildly acidic pH in the endosomal lumen.
(5) Delivery of viral RNA to the nucleus, synthesis of messenger RNA (mRNA) and viral RNA replication.
(6) Synthesis of viral protein components in the cell cytosol (internal proteins) and endoplasmic reticulum (ER) (membrane proteins).
(7) Assembly and budding of progeny viruses

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12
Q

Describe the pathogenesis of Influenza A

A

Replicates in URT and LRT
Peak shedding 2 days, self-limiting 4-7 day

Leads to complex cytopathic effects due to downregulation of host cell protein synthesis and apoptosis, predominantly in the airways epithelial cells

Apoptosis occurs also in lymphocytes explaining the lymphopenia observed during acute infection

IgA and IgG produced

Cell Mediated Immunity important for clearance

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13
Q

How is influenza transmitted?

A

Transmission by aerosol and droplet, lesser extent direct contact

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14
Q

Describe Influenza A epidemiology

A

Maintained in humans throughout the year
- Peak prevalence in winter

Young children major vectors in transmission

Seasonal Influenza - Epidemics every 2 -3 years, often follow school autumn term

  • Indicator – ‘herald wave’ (late spring)
  • Summer outbreaks occasionally seen
  • Annually 3-5 million cases of severe illness
  • Up to 500,000 deaths worldwide
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15
Q

What types of influenza undergo antigenic drift?

A

A and B

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16
Q

What types of influenza undergo antigenic shift?

A

Type A only

17
Q

Describe the host range of influenza

A

HA 1 -16 NA 1 –9
Wild waterfowl natural hosts to all known influenza A subtypes

H1N1, H1N2, H3N2 currently circulating in humans

H5, H7, H9 & N7 also infect humans, but on/limited human-human transmission

18
Q

What are the important determinants for host range and tissue tropism?

A

Epithelial cell surface receptors

19
Q

What 3 conditions are necessary for influenza A pandemic?

A
  1. Emergence of novel Influenza A virus
  2. Ability to cause disease in humans
  3. Human – human transmission
20
Q

By what 2 mechanisms can pandemic influenza originate?

A

The avian influenza virus can replicate and by chance change its receptor to human type, when you can get direct transfer to humans.

A non-human and human virus can get into another host, making reassortant virus.

21
Q

What are the features of Avian Influenza?

A

Most AI do not infect humans
Some cause severe infections in humans
Outbreaks of AI in poultry raise global public health concerns:
~ severe disease in poultry populations
~ potential to cause severe disease in people
~ pandemic potential

22
Q

Describe the pathogenicity

A

All AI is divided into 2 subtypes based on genetic features and/or disease severity in poultry:
Low pathogenic AI (LPAI)
H1 to H16 subtypes
Not generally associated with severe disease in poultry
Highly pathogenic AI (HPAI)
Some H5 or H7 subtypes
High death rates in poultry (up to 100% in 48 hrs)
LPAI H5 or H7 subtypes can mutate into HPAI

23
Q

Describe the features of AI H5N1

A

H5N1 in humans first described Hong Kong 1997 (18 infected, 6 deaths)
Widespread re-emergence in 2003 and 2004
> 600 human HPAI H5N1 reported since November 2003.
Case fatality 60%

24
Q

Describe the features of AI H7N9

A

H7N9 in humans first described China, spring 2013 (132 infected , 44 deaths)
First case outside China reported February 2014 in Malaysia.
Case fatality 33%

No evidence sustained person-to-person spread
Evidence limited person-to-person spread
Slight mutation could convert to a strain transmissible from human to human

25
Q

What is the primary risk factor of AI H5N1 and H7N9?

A

Primary risk factor for humans infection with H5N1 or H7N9 is direct or indirect exposure to infected live or dead poultry or contaminated environments

26
Q

Describe the features of Swine Flu H1N1

A

Novel Influenza strain
Generally mild respiratory illness (severe disease or death in vulnerable individuals)

H1 N1 Reassortment of human and swine influenza viruses. 6 genes from American swine flu (mix of swine, bird & human flu)

HA gene similar to swine flu viruses present in U.S. pigs since 1999 NA and matrix protein genes from European swine flu

27
Q

How does swine flu H1N1 differ from seasonal flu?

A

Unlike seasonal flu, pandemic H1N1 can replicate efficiently in cells deeper in the lung, similar to the more pathogenic H5N1 ‘bird flu’

28
Q

What are the symptoms of swine influenza?

A 
Coughing 
Sore throat
Lethargy 
Lack of appetite
Diarrhea
Sneezing
Watery eyes
Runny nose
Fever 
Weight loss
Poor growth
29
Q

Describe the outbreak history of swine flu H1N1

A

April 2009 outbreaks in Mexico and the USA
June 2009 WHO declared an H1N1 pandemic

January 2010 - transmission in 208 countries,13,554 deaths
Highest incidence in school age children
> hospitalised cases children &young adults (highest 0-4 yrs)
Few cases in older adults but highest case-fatality ratio
70% of hospitalised cases have underlying medical condition

From September 2010
Antigenically unchanged virus circulating
> hospital cases in 40-50 year olds with no underlying medical conditions

30
Q

What are the WHO guidelines for global surveillance of Influenza A?

A

Monitor global occurrence

Identify and characterize emergent influenza strains

Monitor changes in transmission patterns

Monitor unusual morbidity / mortality due to acute respiratory illness

Monitor global activity of influenza viruses in animal/avian populations

31
Q

What are the vaccination types against influenza?

A

Inactivated vaccine
Propagated in eggs or human diploid fibroblast
Purified HA & NA harvested & lipids extracted
- Trivalent vaccines
Protect against 3 strains A/H3N2, A/H1N1, and influenza B

  • Quadivalent vaccines
    Protect against 4 strains of the flu, A/H3N2, A/H1N1, and 2 strains of influenza B
Live attenuated vaccine - Only in Russia, not licenced in UK
Serial passage at 33oC 
intranasal
trivalent
duration of immunity at least 1 year
32
Q

What antiviral therapies are available to treat influenza?

A

Amantadine hydrochloride
Inhibits viral uncoating

Rimantadine hydrochloride
Inhibits viral uncoating

Zanamivir (Relenza)
Neuraminidase inhibitor

Osteltamivir phosphate (Tamiflu) 
     Neurominidase inhibitor

(1st 2 no longer given, immediate resistance. 2nd 2 must be given within 24 hours)

Medical Microbiology (13 decks)

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