6: Arboviruses Flashcards
How are arboviruses transmitted?
Arthropods e.g. biting insects
What MUST happen inside the insect to be classed as an arbovirus?
Infect and replicate inside them
Which species is a vector for over 50 different pathogens?
Culicoides
What kind of hosts are humans to arboviruses?
Dead-end
How do insects become infected?
By feeding on a viraemic vertebrate host
What happens to the virus once it is inside the insect?
Establishes a persistent infection with no harmful effect
How long until the virus can be passed to a new host?
There is a time delay called the extrinsic incubation period
How long does infection last in the insect?
Its whole life span - continual cycling and transovarial infection
What are the four properties of an arthropod vector?
Co-incident and common, correct host preference, susceptible to infection, transmission competent (amplified in salivary glands so bite induces an infectious dose)
Which part of the insect does the virus infect it through?
The midgut, then spreads/replicates
What determines the competence of the vector to be infected through its midgut?
The mesenteron-infection and mesenteron-escape barrier (susceptible vs release into haemocoel)
When vectors “cross-feed” on other species, what are two possible outcomes?
Either becomes viraemic enough to contribute to the life cycle, OR are a dead-end host
How does rain allow vector competence?
Provides breeding site
What does virus replication depend on?
Temperature
So how is EIP controlled?
Temperature
What’s the problem with shorter EIP and higher temp?
Shortens insect life
What are some overwintering strategies?
Reside in eggs/larvae if transovarial, larvae can enter diapause, move indoors, PI host e.g. cattle reservoir, long-lived alternative vector
What are some control options?
Eliminate infected hosts, restrict movement, vaccinate, alter sheep breeding seasons, reduce vector numbers, insecticides, move host indoors at biting times
Where are Culicoides breeding sites?
Wet leaf litter, old dung heaps, waterlogged pasture
What are some direct effects of climate on the vector?
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
What are some indirect effects of climate change on vectors?
Displacement e.g. due to deforestation, irrigation, sea level, and changes to farming and livestock
As well as shortening EIP, what is another problem that faster vector growth rate causes?
Gut leakiness which reduces MIB and MEB so vectors can now transmit to more species and more vector species can transmit
