Heamophillus Influenza

Question 1

Structure

Answer 1

1) spherical : 80-120nm
2) polymorphic, long filamentous forms - during early passages of new isolates
3) genome: (-) ss RNA –> 8 seperate a segments (a&B) type
7 separated segments (c types)
4) enzyme transcriptase RNA dependant RNA polymerase
5) M protein : Matrix
6) Capsid: 8 nucleocapsid fragments, helical structure
7) super capsid
: virus encoded GP into envelope
-HA- Haemaglutinin
-NA- Neuraminidase

Question 2

Antigenic structure

Answer 2

1) HA: represents 25%viral proteins (400-500 molecules) - length 14nm,trimmer ( imparts greater stability)
i) HA1- monomer
ii) HA2 - dimer

Question 3

Virus

Answer 3

-Orthomyoxoviridae influenza virus
- 3 types
- A,B,C
-type A : ( AG changes !!)
Host: human, birds, pigs, horses, seals
Causes: epidemics&pandemics (1918-2mil dead) -Spanish flu
-Type B: (AG changes lesser)
Host: human sometimes causes epidemics
-type , ( Ari for children )
Host: sporadic form, mild disease
-general: 19th haemophilus influenza
-isolated in 1933

Question 4

HA structure

Answer 4

• elongated stalk ( base anchor in membrane)
• capped by a large globule
• pocket located at the too of the globe cellular receptor binding site ( the pocket is inaccessible to AB )
• trimmer HA : non infectious –> cleavage if HA1 and HA3 necessary for virus particle to be infectious ( by cellular protease)

Question 5

Structure of HA gene

Answer 5

-14 alleles encode 14 serological independent , non cross reacting HA subtype h1-h14

Question 6

Three subtypes

Answer 6

• recovered from human H1, H2, H3
• results in appearance of a new subtype
• mechanism for AF shift–> genetic re-assortment between humans and no humans ( especially of avian origin)

Question 7

Functions of HA

Answer 7

1) viral adhesion
2) enhance
The fusion of viral and host cell membrane
3) haemogluttinates RBC (human, chicken, guinea pig)
4) determines production of neutralizing AB–> humoral IR

Question 8

Antigen structure : NA

Answer 8

• cleaves mucin( protective barrier of resp ep allowing HA to attatch
• 5% viral proteins (150mol£ 6nm length
• spike is tetremer, composed of 4 identical
• Monomers:
• slender stalk
• box shaped head
• catalytic site for Neuraminidase on top of each head ( 4 active sites)

Question 9

Function of NA

Answer 9

At end of viral cycle

• facilitates releaser of virus particles from infected cell during budding
• prevents self- aggregation of virions

Question 10

NA gene

Answer 10

• 9 alleles encode 9 serotyoes
• independent NA subtypes
• human A virus 2 NA - N1,N2

NA is target for antivirals:

• zanamivir
• Oseltamivir

Question 11

NP internal protons

Answer 11

9 NP - capsid proteins

• determine the type of specified
• determine intoxication symptoms

Question 12

M proteins (40%)

Answer 12

• M1 –> between capsid and super capsid
• M2–> ion channel protein ( fewer copier per particle)
• target for Amantadine, remantadine

Question 13

Pathogenesis : AG changes

Answer 13

1) Antigenic drift
- minor AG changes because of point mutation in the gene–> amino acid changes in the protein
( virion can escape recognition by hosts immune system)
2) Antigenic Shift
- Major AG changes in NA and HA –> results in the appearance of a new subtype
- The mechanism for AG shift is genetic re assortment between humans and no humans ( especially if avian origin)