28 - influenza virus

Question 1

what are the 3 types on influenza?

Answer 1

A
B
C

Question 2

influenza A

Answer 2

humans, pigs, birds m horses, sea mammals

epidemics every 2-3 years - waning immunity bans antigenic drift

pandemics every 10-40 years - antigenic shift

causes us the most problems

Question 3

influenza B

Answer 3

humans

milder disease

Question 4

influenza C

Answer 4

humans

milder disease

rare

Question 5

transmission of influenza

Answer 5

respiratory route

infects ciliated epithelium cells in the upper respiratory tract

Question 6

how do macrophages causes the endothelial cells to become leaky in the upper respiratory tract in influenza?

Answer 6

macrophages phagocytose lysed cells and virus particles

leads to pro inflammatory cytokines

causes endothelial cells to become leaky

leaky is good as allows IgG antibodies to move out of blood into tissue which causes the runny nose

Question 7

symptoms of infuenza virus infection

Answer 7

runny nose - leaky endothelial barrier

cough - mucus

fever - pyrogens

muscle che s

Question 8

what do pyrogens do?

Answer 8

effect the hypothalamus causing the temperature to rise

Question 9

innate response to the influenza virus

Answer 9

NK cells

type 1 interferon - IFN alpha and beta
• help protect the cells around the infected cells

Question 10

adaptive response to the influenza virus

Answer 10

B cells - antibodies

T cells - CD8+ and CD4+

Question 11

what causes the pandemics and epidemics of influenza?

Answer 11

immune memory fading

at the same time there is evolution of the virus

Question 12

what is antigenic drift?

Answer 12

minor change

mechanism of variation in viruses that involves the accumulation of mutations within the genes that dose for the antibody-binding sites

gradual mutation

leads to epidemics

Question 13

what is antigenic shift?

Answer 13

major change

process by which 2 or more different strains of a virus or 2 strains of different viruses combine to form a new subtype having a mixture of surface antigens of the original stains

reassortment

leads to pandemics

Question 14

what is waning immunity?

Answer 14

the progressive loss of protective antibodies against an antigen or disease that occurs with the passage of time

a crucial factor in vaccination - booster doses are given when the immune rezones to na antigen drops below protective levels

Question 15

structure of the influenza virus

Answer 15

• M1 matrix protein
• M2 ion channel
• PA, PB and PB2 - 3 proteins made by RNA dependent RNA polymerase
• NA neuramidase - cleaves sialic acid
• HA haemagglutin protein - binds sialic acid
• NP - nuclear proteins

Question 16

lifecycle of influenza virus

Answer 16

1) HA binds to sialic acid on surface and is engulfed into membrane
2) reduced pH in the virus particle causes the uncoating of the virus
3) RdRP causes + mRNA
4) leads to translation of viral proteins
• NA, HA, M1, M2
5) virus then needs to leave host cell
6) NA, HA and M1/2 endocytose in virus particle - HA stays stuck to sialic acid on surface
7) NA cleaves sialic acid to release the cell

recap

Question 17

why was the 1918 strain of influenza so virulent?

Answer 17

birds cannot usually infect humans

occasional exceptions - but can’t usually be spread human to human

in 1918, the virus had a mutation that could be passes at a high rate human to human

humans had no defences against it as it was a bird flu

Question 18

vaccines for influenza

Answer 18

killed - subunit, whole or split
• injected
• elderly and high risk respiratory patients

live attenuated
• nasal
• children

Question 19

treating the infection

Answer 19

amantidine - M2 channel blocker

tamiflu - neuraminidase inhibitor - leads to the virus clumping on the surface of the cell - stops the spread