ORTHOMYXOVIRIDAE

Question 1

Genus

Answer 1

(Myxa- mucous)

1. Influenza A, B, C; T
2. Hogotovirus,
3. Isavirus

Question 2

Morphology –

Answer 2

• Enveloped
  -ssRNA genone
  (-ss = negative single strand RNA) (8)
• Helical capsid – (true for all –ssRNA types!)

Question 3

Resistance

Answer 3

Weak (enveloped)

Question 4

Biological properties

Answer 4

Baltimore V – viral transcriptase enzymes

Core = a nucleoprotein (NP) with polymerase - Matrix M1 protein

Question 5

2 key proteins in envelope

Answer 5

Dictate the antigenic properties of virus
1) Hemagluttinin (HA) – virus binds to host cell here

2) Neuramidinase (NA) – for release + spread of virus
+ Matrix M2 protein – ion channel

Question 6

Virulence

Answer 6

Hemagluttinin cut by a protease
(usually Trypsin-like)

In cell mucous
– hence virus infects respiratory organs (Flu!)

Trypsin cuts at certain simple Aa. Sites  virus infects other cells

Question 7

Propogation

Answer 7

Embryonated egg
(allantoic and amniotic membranes)

Influenza A – Euryxen – mainly birds, but also Zoonotic –

Question 8

Antigenic properties

Answer 8

1. Core + matric proteins are conservative
   – A,B, C Genus
2. But envelope proteins (HA, NA) are very diverse – hypervariable
   - Eg HA has 16 Serotypes
   NA has 9 Serotypes
3. Antigenicity depends on HA & NA combination
4. Identification code identifies these –
   Eg - A/equi/Praque/1/56(H7N7)

Question 9

Antigenic drift and shift

Answer 9

1. Antigenic drift – Mutations in HA and NA antigens

2- Antigenic shift – Recombination  new HA/NA combinations
- Hence no protection in population from new combinations - epidemic

Question 10

Diagnosis

Answer 10

Isolation (embryonated eggs) + HA test

Indirect (for Serology) – HAI

Question 11

Influenza A virus

Answer 11

Mainly bird viruses!

• then adapt to other hosts:
• Fever, respiratory symptoms, muscle pain – humans, mammals
• Interferon response
• Infects other hosts – domestic animals, humans

1. Porcine Influenza (H1N1, H3N2)
   – often a bridge to human disease
2. Equine Influenza
   (H7N7 – rarely seen, H3N8 - widespread)
   – vaccines
3. (H3N8) – in Greyhounds – USA
4. Avian Influenza
   – But usually no effect on wild birds
   Esp H5N1 – wild birds  chickens  wild birds  humans
   - 50% mortality in humans

5. Human Influenza 
– Originally from water fowl
- Esp H1N1, H2,N2, H3N2
- “Spanish flu” – 1918
- H1N1 – both porcine and human!

Question 12

Influenza B and C

Answer 12

Human influenza

Question 13

Thogotovirux

Answer 13

Tick bourne

Question 14

Isavirus

Answer 14

Infectious Salmon Anaemia virus (Norway)