6: Arboviruses

Question 1

How are arboviruses transmitted?

Answer 1

Arthropods e.g. biting insects

Question 2

What MUST happen inside the insect to be classed as an arbovirus?

Answer 2

Infect and replicate inside them

Question 3

Which species is a vector for over 50 different pathogens?

Answer 3

Culicoides

Question 4

What kind of hosts are humans to arboviruses?

Answer 4

Dead-end

Question 5

How do insects become infected?

Answer 5

By feeding on a viraemic vertebrate host

Question 6

What happens to the virus once it is inside the insect?

Answer 6

Establishes a persistent infection with no harmful effect

Question 7

How long until the virus can be passed to a new host?

Answer 7

There is a time delay called the extrinsic incubation period

Question 8

How long does infection last in the insect?

Answer 8

Its whole life span - continual cycling and transovarial infection

Question 9

What are the four properties of an arthropod vector?

Answer 9

Co-incident and common, correct host preference, susceptible to infection, transmission competent (amplified in salivary glands so bite induces an infectious dose)

Question 10

Which part of the insect does the virus infect it through?

Answer 10

The midgut, then spreads/replicates

Question 11

What determines the competence of the vector to be infected through its midgut?

Answer 11

The mesenteron-infection and mesenteron-escape barrier (susceptible vs release into haemocoel)

Question 12

When vectors “cross-feed” on other species, what are two possible outcomes?

Answer 12

Either becomes viraemic enough to contribute to the life cycle, OR are a dead-end host

Question 13

How does rain allow vector competence?

Answer 13

Provides breeding site

Question 14

What does virus replication depend on?

Answer 14

Temperature

Question 15

So how is EIP controlled?

Answer 15

Temperature

Question 16

What’s the problem with shorter EIP and higher temp?

Answer 16

Shortens insect life

Question 17

What are some overwintering strategies?

Answer 17

Reside in eggs/larvae if transovarial, larvae can enter diapause, move indoors, PI host e.g. cattle reservoir, long-lived alternative vector

Question 18

What are some control options?

Answer 18

Eliminate infected hosts, restrict movement, vaccinate, alter sheep breeding seasons, reduce vector numbers, insecticides, move host indoors at biting times

Question 19

Where are Culicoides breeding sites?

Answer 19

Wet leaf litter, old dung heaps, waterlogged pasture

Question 20

What are some direct effects of climate on the vector?

Answer 20

Metabolic rate (population size and blood feeding rate), distribution and range, lifespan, reduced duration of VFP and TFP, dehydration reduces survival rates, rain forms breeding sites, wind disperses vectors

Question 21

What are some indirect effects of climate change on vectors?

Answer 21

Displacement e.g. due to deforestation, irrigation, sea level, and changes to farming and livestock

Question 22

As well as shortening EIP, what is another problem that faster vector growth rate causes?

Answer 22

Gut leakiness which reduces MIB and MEB so vectors can now transmit to more species and more vector species can transmit