Influenza Flashcards
What are the 3 main types of the influenza virus?
- Type A
- Type B
- Type 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 two variations dictate the name of virus strains in influenza A?
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 3 characteristics of influenza type B
- Are normally exclusive to humans
- Are not classified by H and N proteins
- Can only cause epidemics, not pandemics
What are the two antigenic lineages of type B influenza?
Yamagata & Victoria
Have been circulating since 1980
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?
Influenza A genome has 8 single-strands of RNA - if/when they become shuffled or replaced, it results in changes in the H and N protein configuration = creates a new subtype
How does the immune system target influenza viruses?
By the spike proteins – if the proteins change, it can affect the virus’s antigenicity
What are the two purposes of the flu vaccine?
- To prevent carriers from spreading the virus
- To develop herd immunity
What is herd immunity?
The resistance of a population to a spread of an infectious disease due to the high proportion of the population that has immunity
Who does herd immunity protect? (2)
- Those who cannot or wall not get vaccinated
- Those who have an incomplete response to the vaccine
What is the purpose of mass vaccinations?
- To obtain herd immunity
- Protect others
What are 3 reasons for vaccine hesitancy?
- Misinformation and mistrust
- Worry for personal safety
- Mismatch or poor uptake
Why are some flu seasons worse than others?
- Poor vaccine match to virus
- Low immunizations rates in the public
- Poor uptake of vaccine
What is antigenic shift?
An abrupt change in H & N protein combination that results in a new/novel combination
Explain 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
Explain antigenic shift 2
**no genetic change to virus occurs
bird strain jumps directly to humans and has potential for human-to-human spread
Explain 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?
Antigenic shift 1 because genetic changes occur and result in a new strain of a virus that humans have little to no protection against
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
What type of antigenic changes is responsible for the need for new flu vaccines?
Antigenic drift - flu vaccines must be updated yearly as the virus continues to modify and become unrecognizable to the immune system’s previously created antibodies
