Influenza Flashcards
3 Types of Influenza Viruses
A, B and C
What is the only type of influenza that can cause pandemics?
Type A Influenza – pandemic occurs when virus crosses from birds to humans and has the ability to pass between humans & people have little to no immunity
What are the primary reserviors of Type A influenza?
Waterfowl - virus found in intestines and is released in feces
Where has ideal conditions for transmission and jumping species of Type A influenza?
Asia - poultry, ducks, pigs, and humans all live in crowded conditions
- also wet-markets
What variations dictate the names for Type A influenzas?
Strains named after their H and N variations
H - Hemaggluttinin
N - Neuraminidase
What is hemagglutinin?
A type of protein spike on influenza viruses that allows the virus to attach to the host cell and enter via membrane fusion
What is neuraminidase?
A type of protein spike on influenza viruses that cuts the host cell membrane, allowing the new virion to be released
What are the only H subtypes of influenza A that have shown the ability to transmit freely among humans?
H1, H2, H3
How many subtypes of influenza A are still circulating in humans and what are they?
H1N1 from 1918
H3N2 from 1968
H2 has stopped circulating
What are the 3 characteristics ofType B influenza
- Exclusive to human
- Cause epidemics but not pandemics (slow to replicate)
- Is not classified by H and N
What are the 2 type B influenza lineages?
Yamagata and Victoria (circulating since 1980’s)
Why can’t Type B Influenza cause pandemics?
Type B viruses undergo antigenic drift less rapidly than Type A viruses
Because they mutate 2-3x slower, there are less subtypes
What hosts are Type C influenza found in?
Humans and Pigs
What are 2 characteristics of Type C influenza?
- Less common than the other two types of influenza
- Triggers a mild respiratory illness, sometimes no symptoms at all
What causes changes in the H and N proteins?
The shuffling or replacing of the 8 strands of influenza A RNA
How does the immune system target influenza viruses?
By the spike proteins – if the proteins change, it can affect the virus’s antigenicity
What is antigenic SHIFT?
Abrupt change where the H and/or N are replaced with new or novel H or H/N combinations that are completely new to the immune system
Herd immunity
When a high % of the population is immune to a disease resulting in less spread
What is the purpose of mass vaccination?
To obtain herd immunity to protect those who did not receive a vaccine or those individuals who may have had an incomplete response to a vaccine
Antigenic shift 1
- Bird passes bird strain to intermediate carrier
- Person passes human strain to the same intermediate carrier
- Viruses infect the same cell = strain genes mix = creates new strain
- New strain passed back to human from intermediate host
Antigenic Shift 2
*** No genetic
a bird strain of influenza A can jump directly from a
duck or other aquatic bird to humans.
Antigenic Shift 3
**no genetic change to virus occurs
bird strain jumps directly to intermediate host, then to humans; potential for human-to-human spread
What type of antigenic shift can result in a pandemic and why?
ALL due to human to human spread and if there is change in genetic material
What is antigenic drift
The continuous process of minor modifications to the virus in circulation as a result of transcription error, resulting in different variants
* when antibodies no longer recognize the variant, reinfection can occur
Why are some flu seasons worse than others?
Vaccine mismatch
Poor uptake of the vaccine
Decreased rate of immunization
