Ticks
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- Created by: fionnualamaire94
- Created on: 05-01-17 19:58
Ticks
- obligate, blood-feeding ectoparasites of vertebrates
- bites may be directly damaging - cause irritation, inflammation, or hypersensitivity, if large numbers - anaemia and production losses
- important in pathogen transmission
- two families of ticks - Ixodidae and Argasidae
- Ixodidae - most important - hard ticks, due to rigid chitinous scutum
- Argasidae - soft ticks, lack a scutum - includes bird ticks
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Ixodidae
- relatively large ticks (2-20mm), flattened dorsoventrally
- enlarged fused coxae of palps - basis capituli
- lower wall extended anteriorly - hypostome (anchors tick when feeding), lies below chelicerae
- palps and chelicerae are anterior and visible from dorsal surface
- have scutum - whole surface male, small area larva/nymph/female
- may have row of notches - festoons on posterior border of body
- gonopore ventral behind gnathostoma
- anal groove posterior to genital grooves and 4th pair of legs
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Ixodidae - Life Cycle
- temporary parasites, single hexapod larval stage, single octopod nymphal stage, reproductive adult stage
- number of hosts variable
- one-host ticks - entire parasitic development on one host
- two-host ticks - larvae and nymphs on one host and adults on another
- three-host ticks - each stage of development on different hosts
- important vectors of protozoal, bacterial, viral and rickettsial diseases
- trans-stadial transmission - pathogen remains in vector throughout cycle
- trans-ovarical - pathogen transmitted to offspring via ovaries
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Ixodes spp.
- largest ixodidae genus - ~250 species
- small inornate ticks, no eyes or festoons, long mouthparts
- anterior position of anal groove - important in identification
- ixodes ricinus - example species
- adult female light grey, 1cm in length and bean shaped, when engorged legs not visible from above, males 2-3mm long, legs visibile
- hosts - sheep, cattle, goat mainly
- not in North America
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Ixodes ricinus - Life Cycle
- three-host tick, 3-year life cycle
- tick only feeds for a few days a year (26-28 total) - in each life stage
- mating takes place on the host
- once fertilised female feeds for about 14 days, drops to ground lays several thousand eggs in soil for 30 days then dies
- eggs hatch and produce larvae
- once host located - larvae feed for 3-5 days, drop back to vegetation digest and moult to nymphs
- nymphs find host next year feed 3-5 days, drop and moult to adult
- host size increases with each moult
- unfed larvae can survive 13-19 months, nymphs 24 months, adults 21-31 months temp/humidity dependent
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Ixodes ricinus - Pathogenesis
- sometimes heavy infections can cause anaemia
- may damage host at site of attachment causing local injury - predisposing to bacterial infections
- transmits pathogens
- Babesia divergens - Western Europe in cattle - red water fever
- Anaplasma marginale - anaplasmosis
- sheep and cattle - louping-ill, and rickettsia causing tick-borne fever
- Borrelia burgdorferi - Lyme disease in humans
- Babesia divergens - Western Europe in cattle - red water fever
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Amblyomma spp.
- large, often highly ornate ticks, with long often based legs
- eyes and festoons present, males lack ventral plates
- long mouthparts - deep, painful bite - secondary infection
- 100 species, central and eastern North America, tropical/subtropical Africa
- three-host tick life cycle
- pathogen transmission
- A. americanum - Rickettsia rickettsi - Rocky Mountain Spotted Fever; Francisella tularensis (tularaemia); Lyme disease, Q fever, canine ehrilichiosis, human monocytic ehrlichiosis
- A. variegatum - Ehrlichia ruminatum - heartwater in cattle; Coxiella burnetii - Q fever
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Boophilus spp.
- 'blue ticks'
- important vectors of Babesia spp. and Anaplasma marginale - in cattle, tropical and subtropical countries
- unfed adults 2-3mm long up to 12mm engorged
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Dermacentor spp.
- medium to large ticks, with ornate patterning
- festoons and eyes present
- most species, three-host ticks, some one-host ticks
- small genus of ~30 species mostly in New World
- several species associated with, Rocky Mountain Spotted Fever, Q Fever, tularaemia, Colarado tick fever, some saliva may produce tick paralysis
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Hyalomma spp.
- medium or large ticks, eyes and long mouthparts
- two-host ticks (some three-host)
- most commonly found on legs, udder, tail or perianal region
- ~20 species Asia, Southern Europe, North Africa
- can survive exceptionally cold and dry conditions
- usually inornate with banded legs, eyes present, sometimes festoons
- pathogens
- H. anatolicum - transmits Theileria annulata, T. equi, Babesia aballi, Anaplasma marginale, Trypanosoma theileri and at least 5 arboviruses
- H. aegyptium - found mainly on tortoises
- H. anatolicum - transmits Theileria annulata, T. equi, Babesia aballi, Anaplasma marginale, Trypanosoma theileri and at least 5 arboviruses
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Rhipicephalus spp.
- genus of ~60 species, originally endemic to Old World, for most part - Sub-Saharan Africa
- three-host ticks (some are two-host)
- pathogen transmission
- R. appendiculatus - vector of east coast fever (Theileria parva); T. lawrencei, Nairobi sheep disease virus; Ehrlichia bovis, Hepatozoon canis, Rickettsia conorii
- R. sanguineus - primarily on dogs - Babesia canis and Ehrlichia canis - can cause tick paralysis; east coast fever in cattle, Rocky Mountain Spotted fever in USA/Mexico
- other infections in animals/humans - Theileria equi, Babesia caballi, Anaplasma marginale, Hepatozoon canis, Coxiella burnetii, Rickettsia conorii, R. canis, R. rickettsi, Pasteurella tularensis, Borrelia hispanica, Nairobi sheep disease viruses
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Argasidae
- soft ticks, have leathery and unsclerotised body with textured surface
- integument is inornate
- palps appear leg-like 3rd/4th segment equal in size
- gnathostoma located ventrally not visible from dorsal view in nymphs and adults
- if present - eyes are in lateral folds above legs
- stigmata are small and anterior to coxae of fourth pair of legs - legs similar to those of hard ticks
hosts - mainly birds in warmer climates but occasionally in humans
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Argasidae - Life Cycle
- ticks are drought resistant and capable for living for several years
- multi-host development cycle
- larva feeds once before moulting to first stage nymph
- between 2-7 nymph stages, each feeds and leaves host before moulting
- adults mate away from the host and feed several times
- adult female lays batches of 400-500 eggs after each feed
- argasids only feed for a few minutes
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Argas spp.
- dorsoventrally flattened ticks with definite margins
- mostly nocturnal, - birds, bats, reptiles or small insectivorus mammals, seldom humans
- A. persicus - breeds in shelters in cracks and crevices in structure of poultry houses
- heavy infestations can take enough blood to bring about death of host
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Ornithodoros spp
- ~90 species, tropical/subtropical habitats in Old and New Worlds
- nocturnal, mouthparts well developed - mainly dens, caves, nests and burrows
- only nymphs and adults are parasitic - considerable irritation
- heavy infestations - mortality of stock from blood loss
- several species inflict painful bites - major vectors of relapsing fever and African swine fever
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Otobius spp.
- small fenus contains only 2 species - Otobius megnini and O. lagophilus
- commonly infests wild and domestic animals - sheep, cattle, dogs, horses, and occasionally humans
- larvae and nymphs feed in external ear canal of host - severe inflammation and a waxy exudate in ear canals - secondary bacterial infection can occur, may extend up ear canal
- infested hosts may scratch and shake their heads - scratching can cause local skin trauma possibly perforating ear drum - infection, ulceration, and in some cases meningitis
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Principles of tick control
- largely based on chemical acaricides - total immersion in dipping bath or spray, shower, spot-on or slow-release ear tags
- organophosphates (malathion, chlorpyrifos, fenthion, dichlorvos, cythoate, diazinon, propetamphos, phosmet) and pyrethroids (permethrin, deltamethrin) - sprays, dips, spot-on, showers
- macrolytic lactones or closantel - parenteral route
- topical acaricidal compounds in companion animals (fipronil, imidacloprid, selamectin, amitraz, and organophosphates and carbamates) - kill ticks on host
- pyrethroids (permethrin, deltamethrin) - not in cats
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