Ectoparasites as Virus Vectors

Question 1

what is an ectoparasite

Answer 1

a parasite that lives on or in the skin but not within the body –> mosquito, midge, tick, flea, louse, sea louse, mite

Question 2

what is a dead end host

Answer 2

host from which infectious agents are not transmitted to other susceptible hosts

Question 3

what is arbovirus

Answer 3

arthropod-borne viruses

viruses which are maintained in nature or through biological transmission between susceptible vertebrate

hosts by hematophagous arthropods; they multiply and produce viremia in the arthropods are passed onto new vertebrates by the bite of an arthropods

Question 4

what are arthropod-borne viruses

Answer 4

arthropods are biological vectors of virus –> the virus replicates within the arthropod which acts as both reservoir (promoting persistence and amplification of the virus) and vector (promoting transmission of virus)

arthropods have major contribution to epidemiology of arboviruses

Question 5

what are examples of arthropod-borne viruses

Answer 5

african swine fever (soft tick)

louping ill virus (hard tick)

equine encephalitis viruses (mosquito)

west nile virus (mosquito)

bluetongue (midge)

african horse sickness (midge)

schmallenberg (midge)

Question 6

how is abroviruses transmitted between arthropods

Answer 6

potential route depends on specific arthropod

1. can be passed on at different stages of arthropod life cycle (eggs, larvae, nymph)
2. by venereal transmission between arthropods
3. by close feeding on vertebrate host

Question 7

what is the lifecycle of arthropod virus

Answer 7

Question 8

how is arbovirus transmitted between vertebrates

Answer 8

by spread of virus between vertebrate host and arthopod feeding

Question 9

what are the consequence of infection of vertebrates

Answer 9

extent of replication and viraemia may differ in different vertebrate hosts –> different hosts may differ in their importance for persistence of arboviruses

Question 10

what are the consquences of arthropods

Answer 10

1. seasonality of clinical disease –> high when arthropod numbers high/environmental conditions support replication
2. potential climate change may impact on global vector distribution –> emerging arbovirus disease in new geographic areas
3. potential for targeting vectors as control strategy for arboviral disease
4. potential for limiting access to vectors as means of control

Question 11

how are arthropods controlled

Answer 11

insect zappers in housing facilities

dips

habitat control

insecticides

release of sterile males

release of good arthropods

Question 12

how is arboviral disease exposure controlled

Answer 12

barriers (clothing, nets), insect repellents, house animals at peak vector times use lights (or lack of)

vaccines (few vaccines available)

surveillance/education

Question 13

what is bluetongue virus

Answer 13

RNA virus - reovirus - non-enveloped RNA virus with segmented genome

antigenically diverse

Question 14

what is the veterinary impact of bluetongue virus

Answer 14

clinical disease in sheep (sometimes cattle)

other important species: cattle (main carriers)

australia, africa, middle east, asia, americas

Question 15

how is bluetongue transmitted

Answer 15

midge vectors

culicoides spp

Question 16

what is the lifecycle of bluetongue and culicoides

Answer 16

female midges feed every 4d (2 month lifespan) –> once infected pass virus in saliva

Question 17

what are the clinical signs of bluetongue

Answer 17

fever, changes to mucous, linings of the mouth, nose (cyanosis of tongue), coronary band (lameness)

reproductive disorder, vascular disease, high morbidity/mortality

Question 18

how is bluetongue virus controlled

Answer 18

serotype-specific vaccination

isolation, insect control

application of contigency plans

vaccination

importation and movement controls

surveillance

BTV is notifiable

Question 19

what is west nile virus

Answer 19

flavivirus

enveloped ssRNA virus

Question 20

how is west nile virus spread

Answer 20

mosquito vector –> culex pipiens

Question 21

what is the veterinary/public health impact of west nile virus

Answer 21

clinical disease in wild and bird and horses and man

zoonotic disease

Question 22

how is west nile virus trasnmitted

Answer 22

primarily by mosquito/bird cycle –> perching birds primary host

Question 23

what does WNV cause in humans

Answer 23

20% infected humans symptomatic - febrile illness

1% infected humans serious neurological disease –> meningitis, paralysis, encephalitis 10% die

Question 24

what does WNV cause

Answer 24

neurological disease in horses

33% case fatality rate

Question 25

how is WNV controlled

Answer 25

1. education
2. mosquito control
3. insect sprays, barriers
4. vaccine - horses only
5. surveillance

Question 26

what is african swine fever virus

Answer 26

asfarvirus

large enveloped virus with 200 kbp DNA genome

Question 27

where is african swine fever endemic

Answer 27

sub-saharan africa

Question 28

what is the natural host of african swine fever

Answer 28

warthogs and bushpigs

Question 29

how is african swine fever transmitted

Answer 29

maintained by sylvatic cycle –> tick/host cycle

Question 30

what does african swine fever virus effect

Answer 30

domestic pigs, fetal pigs, european boars

threat to pig industry

transmitted pig:pig

Question 31

is ASFV in the EU

Answer 31

re-emerging disease

eradicated europe 1990s –> spread to eastern europe and sardinia 2000s

current threat of spread into mainland europe

notifiable disease

Question 32

how is ASFV controlled

Answer 32

1. no treatment
2. no successful vaccine
3. prevent contact with carrier pigs
4. tick control (countries where present)
5. maintenance of disease-free status –> control of pigs/pig meat imports, slaughter policy in event of outbreaks, boiling of swill