Topic 63 - Avian influenza (RED) Flashcards
Definition of avian influenza
An acute febrile disease with respiratory, enteric and central nervous clinical signs if the strain is highly pathogenic. It is mostly subclinical
It is OIE listed and !! notifiable !!
Occurrence of avian influenza
Worldwide, mainly in outdoor farms
Causative agent of avian influenza
Otrhomyxovirus, Influenzavirus A
Influenza serotype causing avian influenza
All HA and NA serotypes in different combinations are found in birds
H5 and H7 are most important though, since they mutate to become highly pathogenic avian influenza
Which proteins are the serotypes of influensa made up of?
NA = Neuraminidase
HA = haemagglutinin
What is the function of HA?
It is the virus surface protein, the antireceptor.
The virus binds to the surface of the cell where we find siliac acid protein which is the receptor.
What is the function of NA?
Its an enzyme.
It is responsible for the release of the virus from the cell.
the enzyme cuts the connection between virus particles and the cell membrane
How does the NA and HA determine serotypes of the influenza, how is it done?
They are hypervariable genes, meaning that most of the mutations happens at the HA and NA genes.
There are serial point mutations, causing a antigenic drift which will make the seasonal influensas
How many types does the NA and HA have, that can cause influensa types?
18 HA types
11 NA types
They combine freely.
The combinations are due to the segmented genome and if two different influensa viruses meet in the same cell, we get a segment re-assortment
Explain how a re-assortment of segments work
1. 2 different influensa viruses meets in the cell
2. They replicate, making copies of the genome segments and at the end, the virus assemble happens ⭢ The segments get into the capsid mixed up
3. At the end of the virus replication, we have one original type virus. But due to the virus re-assortments, we also have two new types.
4. The host already have antibodies working for the original type, but they body do not recognise the new viruses and we get severe clinical signs ⭢ This is what we call the antigenic shift
Natural host of avian influenza
Wild birds. Duck, goose and sawn carry the virus in the intestinal tract
Host susceptible for avian influenza
Poultry = very sensitive
Exotic birds
Wild birds
Route of transmission in case of avian influenza
Direct contact.
Saliva, faeces and natural waters
Migratory birds can play a role in long-distance transmission
What is the difference between highly and low pathogenic strains of avian influenza
Low pathogenic strain
= Might be endemic, but without clinical signs. Let them live, but are culled in the end
Highly pathogenic strain
Every animal is culled !!
The low pathogenic H5 and H7 can mutate to become highly pathogenic
Pathogenesis of avian influenza
- Oronasal infection
- Low pathogenic strain: Causing immunosuppression, enteric and respiratory signs
- Highly pathogenic strain: The blood vessels are damaged and we get systemic infections
