Culicoides and culicoides borne viruses

Question 1

What can culicoides transmit?

Answer 1

Bluetongue, oropouche. African horse sickness. Arvobiruses!

Question 2

What is the size of culicoides?

Answer 2

Tiny! 2-4mm.

Question 3

What is the geographical distribution of culicoides? What kind of habitats do they like?

Answer 3

Almost global except some places such as NZ, hawaii. They like habitats that are full of wet organic matter.

Question 4

Does transovarial transmission of viruses occur?

Answer 4

No the virus is stuck in the adult population.

Question 5

What are the most common hosts for culicoides?

Answer 5

Ruminant hosts (e.g. cows, sheep) and deer and horses. Therefore often in livestock!

Question 6

What is bluetongue virus and in which animals do we mainly see severe disease?

Answer 6

A non-contagious vector-borne virus that affects ruminants. Only really causes serious disease in improved sheep. Cattle are sometimes reservoirs but do not often present with clinical disease. The ONLY vector for bluetongue is culicoides.

Question 7

How many serotypes of bluetongue virus are there?

Answer 7

27. Each serotype has its own characteristics. Each is treated separately and is effectively 27 different diseases.

Question 8

What are the changes in epidemiology that we have seen since 1998?

Answer 8

• Increase in global disease incidence
• Increase in virus diversity in endemic zones
• The emergence of exotic viruses in northern temperate regions.

Question 9

What are the clinical signs of bluetongue virus disease in sheep? (Obviously viral strain-dependent and host-dependent).

What are the acute symptoms?

Answer 9

• Oedema of face
• Fever
• Haemmhorage especially in the mouth
• Nasal discharge
• Inflammation of coronary band (junction of leg hairline and hoof)
• Lameness
• Depression

Most of these are caused by the disruption of epithelial membranes.

Acute:
-Cyanosis of tongue and DEATH.

Question 10

How does bluetongue virus present in cows?

Answer 10

Red mucosal membranes but mostly silent.

Question 11

Describe the transmission cycle of bluetongue between culicoides and host.

Answer 11

• Culocoides picks up virus from viremic ruminant
• Extrinsic inbubation period of 4-20 days in the vectror (temperature dependent- less than 15 degrees is not hot enough to support replication in the vector).
• Virus passes the midgut barrier and goes to the salivary glands
• Culicoides bites a susceptible host
• There is a latency period of 2-4 days before the host becomes viremic

Question 12

How many days is the extrisic incubation period of BTV in the vector?

Answer 12

4-20 days depending on the temperature.

Question 13

What is the optimum temperature for BTV in culicoides?

Answer 13

20 degrees.

Question 14

Which are the two culicoides species in the UK and US respectively that can be bred and hence used as models for study.

Answer 14

C. nubeculosus (UK) and C. sonorensis (US).

Question 15

What percentage of feeding culicoides pick up infection from a viremic host? How are they good vectors nevertheless?

Answer 15

1%. Good vectors due to sheer numbers- one is likely to pick up and transmit infection.

Question 16

When does peak viremia occur in the ruminant host?

Answer 16

4-7 days after infection.

Question 17

Where is the epidemiology of BTV limited to?

Answer 17

40˚ north and 35˚ south. However, this is changing (with climate change etc)!

Question 18

Describe the risk evaluation that took place in the UK in 1993 RE BTV.

Answer 18

• Large population of susceptible ruminants

- But we weren’t sure if our vectors were competent which would, therefore, limit distribution.

Question 19

What is the imicola line?

Answer 19

A “line” representing the distribution of the imicola species of culicoides which is a competent vector of BTV and correlates with the incidence of disease.

Restricts the incidence of disease and means BTV is not really seen in Europe except occasionally in the Iberian peninsula. This was in 1998, however more recently, the range of imicola has expanded into Europe (Spain, France and Italy).

Different serotypes of BTV were coming into Europe from three different populations of imicola.

Question 20

When and where did worrying outbreaks of BTV occur outside of Europe?

Answer 20

2009 in Sweden and Norway! Not seen before in Scandanavia.

Question 21

What is the bluetongue serotype found in the UK?

Answer 21

BTV(F)8.

Question 22

How is it postulated that BTV8 arrived in the UK? How do we know this is not true?

Answer 22

Possible windborne incursion- usually wind blows the insects back to the continent however there was one weather event which may have facilitated the blowing of culicoides into the UK.

This may not be true because we dont have imicola and the serotype was not on the periphery of the EU.

Question 23

What was flagged as the probable cause of spread of BTV8? Why?

Answer 23

Climate change. Because it increases culicoides activity, increases virus replication and there is an overall strong association.

Question 24

Winter is a barrier to bluetongue. What are the 4 potential ways in which BTV can survive the winter to be transmitted when the weather gets warm again?

Answer 24

• Transovarial transmission- infectedeggs wait until spring to hatch
• Adult midges may survive (below 0 degrees midges DIE)
• Infection may persist in host
• Transplacental transmission to ruminant offspring (however colostrum carries anti virus antibodies if the mother was infected).

Question 25

What happened in dairy cattle in North Rhine Westhalia? What was implicated to cause and transmit it?

Answer 25

Dairy cows affected by SCHMALLENBERG VIRUS (novel orthobunyavirus) had the following symptoms:

• A decrease in milk production
• Congenital defects
• Fever

Thought to be a novel orthobunyavirus and based on phylogeny it was thought to be transmitted by mosquitos or midges so a study was carried out where midges were caught and tested- tested positive for carrying the virus.

Question 26

What type of virus is BTV?

Answer 26

An orthobunyavirus

Question 27

What is the main risk of schmallenberg virus?

Answer 27

The TIME of infection is hugely important as while there are only mild symptoms in adults, devastating effects can occur in the foetus/ newborn.
Infection in the SECOND trimester causes problems.

Question 28

How was schmallenberg transmission by culocoides confirmed by a laboratory model? (3 ways)

Answer 28

1) Culocoides inoculated, , incubated, dissected and PCR was done for Schmallenberg RNA
2) Culicoides sonorensis fed on infected blood meal and PCR done on whole insect
3) As above but using culicoides nubeculosus