vector borne diseases

Question 1

what are vector borne diseases

Answer 1

illnesses caused by parasites, viruses and bacteria that are transmitted by vectors

Question 2

what is a vector

Answer 2

a living organism that transmits an infectious agent from an infected animal to a human or another animal
eg mosquitos, ticks, fleas, flies, lice

Question 3

why do vector borne disease have complex etiology

Answer 3

have 3x wider range of carriers (host) compared to non-vector diseases - multiple species can be hosts or reservoirs
individual vector borne pathogen can be transmitted by multiple vector species

Question 4

amplifying host

Answer 4

an organism in which an infectious agent that is pathogenic is able to replicate rapidly and to high concentrations

Question 5

dead end/incidental/accidental host

Answer 5

an organism that generally does not allow transmission

Question 6

4 taxa of pathogens transmitted by arthropods

Answer 6

nematodes
protozoa
bacteria (and rickettsia)
viruses

Question 7

4 types of biological transmission

Answer 7

propagative
cyclopropagative
cyclodevelopmental
vertical and direct

Question 8

propagative transmission

Answer 8

when the organism ingested in blood meal undergoes simple multiplication in the arthropod
eg Arboviruses replicate extensively in tissues of mosquitos, flies and ticks and are transmitted to new host in salivary fluid of arthropod

Question 9

cyclopropagative transmission

Answer 9

the pathogen undergoes a development cycle as well as multiplication in the arthropod
eg malaria in which 1 zygote can give more than 200,000 sporozoites

Question 10

cyclodevelopmental transmission

Answer 10

the pathogen undergoes a developmental change but does not multiply
eg a single microfilaria ingested by a mosquito may result in only one 3rd stage infective larva. in most cases, the number of infective larvae is lower than number of microfilaria ingested in blood

Question 11

vertical and direct transmission

Answer 11

TOT - transovarial transmission
vertical
TST - trans-stadial transmission
venereal

Question 12

co-feeding transmission

Answer 12

when infected and uninfected vectors feed in spatiotemporal proximity to each other on the same reservoir host
the host acts as a transient bridge that brings infected and uninfected ticks together in the same place and time to facilitate pathogen exchange

Question 13

extrinsic incubation period

Answer 13

the period of time the pathogen needs to develop inside the arthropod and to progress to the stage at which it can become infective and can be transmitted
generally 7-14 days
depends on pathogen, vector, temp etc

Question 14

successful mechanical transmission depends on

Answer 14

the degree of contact that vector has with the host and on feeding behaviour (tabanid flies)

Question 15

successful biological transmission varies greatly among species and geographical strains and depends on

Answer 15

innate susceptibility to infection
host preference, blood feeding and resting behaviour of vector
population density of vector and human/animal host
longevity, flight behaviour and oviposition of vector population are intrinsic factors that depend on extrinsic factors eg wind, temp, rainfall etc

Question 16

leaky gut phenomenon

Answer 16

mosquitos ingesting animal blood containing both microfilariae and certain arboviruses have a higher viral infection rate

Question 17

signs of arbo virus infections

Answer 17

febrile disease and non specific symptoms eg
neuro signs, haemorrhage, abortion and vesicular stomatitis

Question 18

arbo virus families

Answer 18

flaviviridae - WNV, TBEV, yellow fever
rhabdoviridae - vesicular stomatitis
togaviridae - eastern equine encephalitis virus
asfaviridae - ASF

Question 19

West Nile fever

Answer 19

mosquito vector, horse and human dead end hosts
genus = flavivirus
most horses down display clinical signs
if they develop neuro signs - 30% fatality
improvement in 3-7 days, full recovery in 6 months

Question 20

African swine fever

Answer 20

genus asfivirus - DNA
epidemiology complex and varies depending on environment, type of pig production system, presence/absence of competent ticks and wild pigs and human behaviour
signs and mortality vary depending on virulence of virus, type and species of pig,
peracute, acute, subacute and chronic forms

Question 21

schmallenberg virus

Answer 21

genus orthobunyavirus
transmitted by Culicoides (midges)
infection of adult ruminants causes non specific signs or goes subclinically
abortion, stillbirth, malformed newborn

Question 22

vesicular stomatitis

Answer 22

genus - vesiculovirus
in cattle, horses, pigs plus sheep and goats
transmission direct contact and biological vectors - black sand flies (other insects can be mechanical vectors)
vesiculation, ulceration and erosion of tongue, oral and nasal mucosa, coronary bands and teats

Question 23

vector borne bacterial diseases

Answer 23

biological vectors mostly ticks - Lyme disease, ehrlichiosis, anaplasmosis etc
transmission by other arthropods is possible eg Ctenocephalides felis - Bartonella henselle

Question 24

Lyme disease

Answer 24

Borrelia burgdorferi - family Spirochaetaceae
vector = Ixodes sp
cause a switch in expression of proteins - OspA to OspC
bacteria exit gut and disperse through hemolymph into salivary glands where they are transmitted to host via expelled saliva
no transmission on first day, inefficient transmission on second day and extremely efficient transmission during 3rd day of nymphal feeding

Question 25

parasitic vector borne diseases

Answer 25

protozoa - babesiosis, leishmaniasis, hepatozoonosis
nematodes - D.repens, D.immitis, Thelazia, Dipylidium caninum