Pathogenesis of Acute and Persistent Infections Flashcards
What is the pattern of an acute infection?
A single peak and a swift resolve
What is the pattern of a latent infection?
Multiple peaks with multiple resolves - bursts of acute infection
What is the pattern of an asymptomatic persistent infection?
Virus is produced all the time with no symptoms - virus production remains high with no resolve
What is the pattern of a pathogenic persistent infection?
Peaks of high viral production with resolution but with a constant low level viral production - never fully clears
Describe the features of an acute infection
- Rapid onset of viral reproduction
- Short but potentially severe disease course
- High viraemia
- Immune clearance
What are the benefits to the virus of a persistent infection?
- Continued virus production and transmission of viral genetic material
- With low or no fitness cost to the host, multiple infections generate genetic variability and complexity
- Host’s health not significantly affected (short term), allowing the virus to disseminate to more hosts (same or new environment)
What are the benefits to the host of a persistent infection?
- Persistently infected organisms are resistant to super infections with related viruses (viral accommodation)
- Persistently infected populations can carry and transmit viruses to sensitive populations and eventually settle and/or replace them
- Organisms persistently infected with mutualistic viruses show an increased antiviral response
- Mutualistic viruses can help the host by supplying new genes or through epigenetic changes - can become part of our genome
Describe the typical acute infection course
- Viral entry
- Viral sensing and innate defenses
- Infection establishes
- Adaptive response is induced
- Memory created
- Virus clearance
What is the incubation period?
- Before the symptoms are obvious - measurable and visible
- At the very start of the infection
- Corresponds to time until prodromal symptoms - symptoms before those characteristic of the disease
Is transmission possible in the incubation period?
Yes
What does a short incubation period suggest?
Replication at primary site produces symptoms
What does a long incubation period suggest?
Symptoms occur beyond primary site of infection
What are unapparent acute infections?
- Successful infections
- No symptoms or disease
- Sufficient viral particles produced to spread in the population
- We know we’ve had them due to antibodies
What are the types of Influenza virus?
A, B and C types
Which Influenza type is responsible for pandemics?
A
Which Influenza types cause serious illness?
A and B
Describe antigenic variation
- Shift and drift
- Allows for constant emergence of new strains
Describe Influenza transmission
- Droplets produced during coughing, sneezing and talking
- Contact with contaminated surfaces and then touching our eyes, mouth or nose
- Direct contact with infected individuals
How far can droplet types spread?
- Large infectious droplets = up to 1m
- Small infectious droplets = up to 2m
- Infectious droplet nuclei = over 50m
Describe the pathogenesis of Influenza
- Invades the mucosal surface
- Movement of mucus usually facilitates the downwards movement of the influenza virus
- Spreads in the respiratory tract by replicating in epithelial cells
- Replication in the bronchioles can lead to severe damage in respiratory capacities
- Lower the virus replicates in our respiratory tract the more acute the symptoms become
- Surface receptors determine susceptibility to human vs avian viruses
- Avian = alpha(2,3) sialic acid which is mainly located in the lower respiratory tract and in the cornea
- Human = alpha(2,6) sialic acid which is mainly located in the upper respiratory tract
- Therefore more susceptible to human respiratory viruses
Describe what a human will experience with uncomplicated Influenza
- 1-5 days incubation - depending on the dose and immune status
- Rapid onset of headache, cough and chills
- High fever peaking up to 40 degrees within 24 hours - malaise and myalgia
- Days 2-3 = fever drops - gone by day 6
- In elderly, children or immunocompromised symptoms may worsen or differ
What dictates Influenza pandemic potential?
- Avian viruses re-assorting with human viruses may lead to efficient transmission
- Avian viruses aren’t efficiently transmitted due to lack of avian receptor in the upper respiratory tract
- If an avian influenza virus re-assorts to exchange genetic fragments with a human virus it may create a hybrid avian human virus that will have characteristics of both
- May be able to transmit efficiently from human to human leading to infection with a virus we have very little immunity for so symptoms could be very severe
How are people infected with avian Influenza?
- Direct contact of people working with chickens or birds
- Contaminated surfaces - e.g. bird droppings
- Dissemination of droplets in the air by infected birds - e.g. flapping wings, scratching, shaking their heads
What are the complications of Influenza?
- Primary viral pneumonia
- Secondary bacterial infections
- General muscle pain
- Cardiac pain
- Reye syndrome - rare - brain swelling
