Orbiviruses

Question 1

What is an orbovirus

Answer 1

Virus of the genus orbivirus within the family of reoviridae
Transmitted by culicoides biting midges, mosquitos and ticks,

Question 2

What is an arbovirus?

Answer 2

a virus that typically infects arthropods and vertebrates
They are named for their typical circular/spherical shape

Question 3

What is a biological vector?

Answer 3

Where the virus replicates inside of the vector
vector acts as just another host
Once infected they remain fully transmissable for life

Question 4

What is a mechanical vector?

Answer 4

Where the virus is just stuck to the surface
Vector does not act as another host
Virus is only infectious for a few hours/days

Question 5

What is the definition of vector competence?

Answer 5

Percentage of individuals that are able to transmit after taking up a virus

Question 6

What is the extrinsic incubation period?

Answer 6

The time it takes for the virus to replicate in the vector and reach the salivary gland

arthropods can only transmit the virus if the salivary gland is reached

Question 7

Why may arthropod borne diseases be on the rise?

Answer 7

Warmer temperatures mean that viruses replicate faster, and there is a quicker insect lifecycle

Question 8

What is the problem with segmented genomes?

Answer 8

immunity is homologous therefore an animal can only be protected if the vaccination is from the same serotype

Question 9

What is the pathogenesis of bluetongue in the mammalian host?

Answer 9

Infection and replication of leukocytes -> distribution everywhere in an animal (effect on the immune response)

infection and replication in the endothelial cells of blood vessels -> direct damage to vascular capillaries through viral replication in endothelial cells -> indirect damage to vascular capillaries by the immune response to endothelial cells

Question 10

How can endothelial cells die?

Answer 10

• Viral replication causing cell lysis
• viral replication causing apoptosis
• viral replication

Question 11

What are the typical signs of bluetongue in sheep?

Answer 11

• Fever
• reduced appetite, lethargy and depression
• reddening of the conjunctiva
• salivation
• decreased production and wool loss
• reduced fertility/ abortion

Question 12

What are the clinical signs of BTV-8 in cattle?

Answer 12

Production loss especially through increased abortion, infertility and transplacentally infected offspring

Question 13

What are the four divisions of AHS?

Answer 13

1. Horse sickness fever : fever and mild oedema of supra orbital fossa (SOF)
   Immune horses & non-horse equids (mules, donkeys) no mortality
2. Sub acute (cardiac) : Incubation 7-14 days
   Subcutaneus oedema (head, neck, SOF), congested conjunctivae, colics.
   Horses: Mortality up to 50%
3. Acute (mixed): Incubation 5-7 days.
   Pronounced oedema, mild pulmonary signs.
   Horses : Mortality up to 80%
4. Peractute (pulmonary): Incubation 3-5 days.
   Marked depression and sudden fever, respiratory distress, frothy fluid
   discharged from the nares
   Horses: Mortality >90%

Question 14

What is the host range of orboviruses?

Answer 14

Domestic and wild ruminants, equines, marsupials, sloths, bats, birds and humans

Question 15

Name three important orbiviruses

Answer 15

• Bluetongue virus
• African horsesickness virus
• Epizootic haemorrhagic disease virus

Question 16

What happens once the virus has reached the salivary gland?

Answer 16

The arthropod is infected for life

Question 17

What is the generalised pathigenesis in a mammalian host?

Answer 17

• Infected midge deposits the virus into the skin
• Virus is then drained to the regional lymph node
• There is then early virus replication
• virus spreads through to other lymphatic organs in a transient viraemia
• virus replication in the endothelial cells

Question 18

What is the msot common vaccine type for both bluetongue and african horse sickness

Answer 18

Live attenuated vaccine