Ectoparasites (Ticks, Mites, Fleas, Lice, Flies/Myiasis)

differences between hard (ixodidae) and soft ticks (argasidae)

hard ticks: hard outer covering (scutum), can see mouthparts from dorsal view
soft ticks: leathery, soft covering, cannot see mouthparts from dorsal view

describe general tick morphology

• large enough to be seen without magnification

• 8 legs (4 pairs)

general tick life cycle (stages)

egg → larva (seed tick) → nymph → adult

how is a many-host tick different from a three-host tick?

three-host ticks have a different host after each molt

many host ticks have a different host after each molt and > 1 nymph stage

what is the only way a one-host tick could spread disease?

if the tick already had the disease as an egg

term for tick or mite infestation

acariasis

describe clinical signs of tick infestations

• bite wounds

• annoyance

• blood loss → anemia if many ticks

• tick paralysis due to toxins in the saliva of certain tick species → neurologic signs like weakness and paralysis

describe the process of tick removal

• grasp tick with forceps close to the patient’s skin

• steady, firm traction

• mouthparts, if possible, but ok to leave in because body will eliminate

• gently cleanse patient skin and wash hands

major drug classes to treat tick exposure

• pyrethrins and permethrins

• isoxazolines

• macrocyclic lactones (some)

which major drug class also repels ticks?

pyrethrins and permethrins

which major class of ectoparasiticides is toxic to cats?

permethrins

ixodes scapularis (“deer tick”)

ixodes scapularis (“deer tick”)

in Ixodes scapularis, describe:

• # of hosts

• identifying characteristics

• transmissible diseases

• three-host species (most)

• anal groove

• Anaplasma phagocytophilum, Borrelia burgdorferi (Lyme disease)

Dermacentor variabilis (“american dog tick”)

Dermacentor variabilis (“american dog tick”)

in Dermacentor variabilis, describe:

• # of hosts

• identifying characteristics

• transmissible diseases

• three-host ticks

• festoons, ornate

• tick paralysis, Rickettsia rickettsii (Rocky Mt. Spotted Fever, or RMSF)

Rhipicephalus sanguineus (“brown dog tick”)

in Rhipicephalus sanguineus, describe:

• # of hosts

• identifying characteristics

• transmissible diseases

• three-host tick

• hexagonal basis capituli, festoons

• Ehrlichia canis, RMSF, babesia canis

Rhipicephalus annulatus (“cattle tick”)

Rhipicephalus annulatus is a how many host tick?

ONE-host tick, unlike the others

which tick species is eradicated in the US and is reportable?

Rhipicephalus annulatus

what disease does Rhipecephalus annulatus carry?

Babesia bigemina (Texas tick fever)

Amblyomma americanum (“lone star tick")

in Rhipicephalus sanguineus, describe:

• # of hosts

• identifying characteristics

• transmissible diseases

• three-host tick

• very long mouthparts, festoons, ornate (female has white spot as well)

• tick paralysis and a variety of bacterial diseases

Otobius (“spinose ear tick”)

what species is otobius found on?

cattle

in Otobius, describe:

• # of hosts

• identifying characteristics

• causes what medical conditions?

• one-host tick

• soft tick, violin shaped, spines

• otitis externa (ear infection)

T/F: you can see most mites without magnification

false, most cannot be seen without magnification

general mite life cycle (stages)

egg → larvae → nymph(s) → adult

PPP of mites

2 - 4 or 5 weeks

how are mites transmitted?

animal-animal contact or close skin to skin contact (mites cannot jump like fleas)

which mite species does not always cause itchiness?

demodex mites

“Big Three” for ddx in dermatitis with pruritis (itchiness)

1) parasites (fleas, mites, lice)

2) infection (bacterial, yeast)

3) allergic dermatitis

diagnostic test(s) for demodex mites

deep skin scrape, trichogram (hair pluck)

diagnostic test for sarcoptes mites

superficial skin scrape

diagnostic test for cheyletiella mites

acetate tape prep

diagnostic test for psoroptes or chorioptes mites

skin scraping

how would you diagnose ear mites with an ear swab?

must evaluate chunks of ear debris, not just ear swap smeared/rolled onto a slide

major drug classes of mite parasiticides

• macrocyclic lactones

• isoxazolines

• pyrethrin and synthetic pyrethroids

what should you consider when treating mites?

you will often need > 1 treatment because eggs are often resistant to tx → retreat in 2-4 weeks

• name

• host

• infection site

• diseases transmitted

• demodex

• many mammals (both SA and LA)

• hair follicles, sebaceous glands

  • localized: often head and limbs (if young animals)

  • generalized: if immunosuppressed

• alopecia, crusts ± erythema → often NOT itchy

• name

• host

• infection site

• diseases transmitted

• cheyletiella

• cats, rabbits, dogs

• skin and haircoat

• “walking dandruff”, mild pruritis

⭐️ note large palpal claws

• name

• host

• infection site

• diseases transmitted

• sarcoptes

• SA (dogs, cats, rabbits, ferrets) and LA (horses*, cattle, pigs)

• skin of ear margins, lateral tarsi, and elbows

• sarcoptic mange or “scabies,” intense pruritis

⭐️ note long, UNsegmented pedicels

• name

• host

• infection site

• diseases transmitted

• psoroptes

• LA and rabbits

• LA → tail region and shoulders, rabbits → ears

• pruritis

⭐️ note long, segmented pedicels

• name

• host (hint: cats)

• infection site

• diseases transmitted

• otodectes

• CATS, dogs, ferrets

• ear canals

• ear pruritis, otitis externa, “coffee grounds”

• name

• host (hint: LA or rabbits)

• infection site

• diseases transmitted

• chorioptes

• LA or rabbits

• LA → tail and LEGS (unlike psoroptes), rabbits → ear

• pruritis

how to differentiate between otodectes and chorioptes?

must know host!

• if cats, likely otodectes

• if LA or rabbits, likely chorioptes

general flea life cycle (stages)

egg → larvae (L1-3) → pupa → adult

PPP of fleas

3-8 weeks

Ctenocephalides felis or “cat flea”

what is something to consider when treating fleas?

95% of the flea population is in the environment, not on the host. You MUST treat the environment as well.

major drug classes used to treat adult fleas

• pyrethrins and synthetic pyrethroids

• Isoxazolines

drugs used to target flea eggs

insect growth/development regulators like METHOPRENE

Xenopsylla, the rat flea

Cediopsylla, the rabbit flea

name, host, and chewing or sucking?

Trichodectes, dog, chewing

name, host, and chewing or sucking?

Felicola, cat, chewing

name, host, and chewing or sucking?

Damalinia, cattle/horse, chewing

name, host, and chewing or sucking?

Haematopinus, cattle/horses/pigs, sucking

name, host, and chewing or sucking?

Linognathus, dogs and cattle, sucking

name, host, and chewing or sucking?

Solenopotes, cattle, sucking

major drug classes that treat lice?

• permethrin

• macrocyclic lactones

• isoxazolines

general lice life cycle (stages)

Nit (egg) → nymph (1-3) → adult

life cycle duration of lice

2-3 weeks

term for an infestation of lice

pediculosis

what do chewing lice feed on?

• skin secretions and debrit

• dried blood

• fur/hairs

what do sucking lice feed on?

• blood

• tissue fluids

a heavy infestation of lice could lead to what medical condition?

anemia

differentiate obligatory vs facultative myiasis

obligatory: animal host is required in fly life cycle

facultative: animal host not required for development of larvae

general fly life cycle (stages) (with details)

egg → larvae (L1-3) → pupa → adult

• eggs hatch and larvae migrate to target tissues

• larvae grow and molt

• drop to ground and pupate

• pupa → adult → lay more eggs~!

• name

• host

• target tissue

• identifying features

• hypoderma

• cattle

• deposit into distal limbs (“heel flies”) and migrates to esophagus/shoulder region

• no spines, spiracles

life cycle duration of hypoderma

~ 10 - 12 months (“about a year”)

treatment of hypoderma

• manual extraction of grubs with hydrogen peroxide

• systemic: macrocyclic lactones to kill developing larvae

• name

• host

• target tissue

• identifying features

• Gasterophilus

• horses

• larvae enter oral cavity and target stomach/GI tissue

• ridges with tiny spines in rows, spiracles

treatment of gasterophilus

• oral macrocyclic lactones

• name

• host

• target tissue

• identifying features

• Cuterebra

• SA → rabbits and rodents, sometimes dogs and cats

• enter natural orifices and target SQ (often neck/head)

• tan to brown, tiny spiracles

treatment of cuterebra?

• carefully extract larvae intact

• flush wound cavity and DO NOT SUTURE SHUT

• name

• host

• target tissue

• identifying features

• screwworm (Cochliomyia)

• animals

• HEALTHY TISSUE

• screwlike spirals

name the two facultative myiasis fly species

• flesh flies (Sarcophaga)

• blow/bottle flies (Lucilia)

what causes wool/fly strike?

flesh flies and blow flies