Ticks

Question 1

What is the importance of ticks?

Answer 1

Blood losses (large numbers  anaemia)
Tick worry (prevent animals feeding)
Disease transmission
Tick paralysis (ascending motor paralysis)
Secondary infection / blowfly strike (at bite site)
Production losses (farm animals)

Question 2

Hard ticks

Answer 2

Important in temperate and warmer climates
Hard dorsal covering on scutum
Prominent mouth-parts
Festoons may be present (bulges on posterior edges)
Ornate ticks have coloured patches
Body wall is convoluted to accommodate blood meal (esp. female ticks)

Question 3

Soft ticks

Answer 3

More important in warmer climates
Absent scutum
Mouthparts not visible from dorsal surface
Do not swell much (feed little and often)

Mouthparts:
Palps - sensory organs
Chelicerae - puncture skin
Hypostome - tube for sucking blood, backward pointing teeth

Question 4

Ticks feeding

Answer 4

Tick stands upright
Chelicerae cut through skin  pool of blood
Hypostome inserted deep into skin
Mouthparts CEMENTED in place
Tick feeds continuously + injects saliva (contains substances that decrease host inflammatory response, ^ permeability of blood vessels -> free flow of blood)

Question 5

Tick life cycle

Answer 5

eggs -> larva -> larvae -> nymphs -> adult

Question 6

Hard tick life cycle

Answer 6

Classified according to number of different hosts to which they attach during their life cycle:
ONE-host ticks: each stage (larva + nymph + adult) feed on one host, e.g. Boophilus
TWO-host ticks: larvae + nymphs feed on one host; adult ticks on a second host, e.g. Hyalomma
THREE-host ticks: each stage feeds + develops on a different host, i.e. three hosts, e.g. Ixodes

Question 7

Soft tick life cycle

Answer 7

NOT classified like hard ticks
Feed little and often on many hosts

Question 8

Trans-stadial transmission

Answer 8

Infectious agent ingested during feeding by larva
Passed on from one host to the next (in 2- & 3-host ticks) as tick develops to nymph + adult
NOT passed onto next generation via the egg

Question 9

Trans-ovarial transmission

Answer 9

Infectious agent is passed from one generation to the next through the egg, e.g. Babesia spp.

Question 10

Ixodes spp. (3-host hard tick)

Answer 10

Worldwide
I. ricinus, most important tick in UK
Distribution: western UK (mainly)
Wide host range
Vector for HUMAN disease: Lyme disease (humans, dogs)
Vector for ANIMAL disease: Bovine babesiosis, louping ill, tickborne fever & tick pyaemia
Paralysis in humans, dogs (warmer climates only)

Question 11

Ixodes ricinus epidemiology

Answer 11

THREE-host tick
Life cycle: 3 years (range, 2-7 years)
Ticks feed for a few DAYS each year
MOST of the time – on the ground
Need high Relative Humidity (RH) (>90%) – in matted vegetation (e.g. rough grazing, hedgerows)
Tick activity seasonal, e.g. spring
Dependent on temp and rh

Question 12

Amblyomma spp. (3-host tick)

Answer 12

Warmer climates, worldwide
Vectors for heartwater (Cowdria ruminantium, Africa); also, Q-fever, Rocky Mountain Spotted fever in southern USA

Question 13

Boophilus spp. (hard 1-host ticks)

Answer 13

Warmer climates worldwide, except Europe
Vectors for Babesia and Anaplasma spp. in cattle

Question 14

Dermacentor spp. (hard 3-host ticks)

Answer 14

Vectors for:
viral (tickborne encephalitis, Colorado tick fever),
rickettsial (Rocky Mountain Spotted fever, bovine anaplasmosis),
bacterial (tularaemia) and
protozoal (babesiosis) diseases

Question 15

Hyalomma spp. (hard 2/3-host ticks)

Answer 15

Warmer climates, Old World
Wide host range
Vectors for Theileria and Babesia spp.
H. aegyptium found on tortoises (Africa; pet shops, UK)

Question 16

Rhipicephalus spp. (hard 2/3-host ticks)

Answer 16

Warmer climates worldwide
Vectors for Theileria parva (East Coast Fever), Babesia bigemina (ruminants, Africa), B. canis, Ehrlichia canis (canine pancytopenia)
Paralysis in livestock

Question 17

Argas spp. (soft tick)

Answer 17

Infect birds in warmer climates (also humans)
A. persicus, poultry tick (or “tampan”), lives in crevices in poultry houses
Feeds at night  production loss + death (large numbers)
Found on migratory birds in temperate regions

Question 18

Principles of tick control

Answer 18

Integrated parasite control: Parasite control programmes that do not rely solely on drug treatment

Question 19

Methods of tick control 1

Answer 19

Killing ticks on the ground -
By altering microclimate: pasture improvement, e.g. cultivation, drainage
By starving: “spelling” pasture (livestock removed); useful only if ticks don’t feed on other hosts
By burning: e.g. during dry period before rainy season

Question 20

Methods of tick control 2

Answer 20

Separate host from infection-
Stock management: remove stock from tick-infected areas when ticks are active
Fencing: fence off infested pastures

Question 21

Methods of tick control 3

Answer 21

Kill ticks on host-
Acaricides: dipping, spraying, pour-on formulations

Question 22

Methods of tick control 4

Answer 22

Enhance host resistance-
Stock hybridisation: e.g. Bos indicus (humped breeds) x Bos taurus (European breeds). Heritability of resistance to ticks is higher in humped breeds than European breeds

Vaccination: a vaccine is now used in Australia for Boophilus microplus control -> raises antibodies against “hidden antigens” in the tick’s gut