6.3 Arthropods 3 Flashcards
mites are in what class
Arachnida
Mites; General types of mites
- itch and mange mites
- bloodsucking mites
- mites in the respiratory system
- mites in the subcutaneous tissues
Mites; Morphology
- Smaller than ticks with membranous cuticle
- Capitulum or “false head”
- anterior and terminal
- mouthparts - hypostome is unarmed
- 4 pairs of legs as adults
- Larvae look like adults but have 3 pairs of legs
- Nymphs look like adults with 4 pairs of legs but are not sexually mature
Mites; General Life Cycle
- all have simple metamorphosis
- life cycle completed on one host, host specific
- all follow the general plan of egg to larva to nymph to adult
- feed on hair, fur, skin, secretions, etc.
- diverse morphological variations depending on host and location on host
Life Cycle - Mites
Egg > Larva (3 pairs) > Nymph (4 pairs) > Adults (4 pairs)
Sarcoptes scabiei diseases
scabies/sarcoptic mange mite, itch mite
Sarcoptes scabiei; general hosts, site of infection
- wide variety of hosts - specific strains for each
- Sarcoptes sp. burrow into stratum corneum
Sarcoptes scabiei; Adult morphology
- oval, short-legged mite with posterior two pairs not extending beyond edge of body
- body has many spines, particularly on dorsum
- pedicels of pretarsi are long and unsegmented
Sarcoptes scabiei; Life Cycle, transmission
- all stages on one host, short survival off host
- females tunnel into epidermis and lay eggs
- larvae, nymphs and newly emerged adults found in skin pockets
- transmission by direct contact
Sarcoptes scabiei; Pathogenesis
- burrowing mites - secretions and excretions may lead to hypersensitivity
- self inflicted damage may cause alopecia and bleeding leading to scabbing
- secondary infections common and may progress to pyoderma
- emaciation and death may result
Sarcoptes scabiei; Lesions/Clinical Signs, predilection sites
- initial papule ruptures and exudes serum, pruritus evident
- progresses to thickened, dry, flaky, skin (hyperkeratosis
and exfoliation) with scabbing and alopecia - chronic disease may continue for months with continuing pruritus - initial lesions usually in less haired areas
- predilection sites:
-dogs - head, ears, elbows, hocks, ventral body
-ruminants - head and neck
-pigs - head around ears, nose and eyes, inner thighs
Sarcoptes scabiei; Diagnosis
- skin scrapings with a glycerine covered scapel performed at the edge of a lesion - examine microscopically
- detritus from a scraping may be digested using 5% potassium hydroxide (near boil)
- mites may be mounted in Berlese solution
Sarcoptes scabiei; Treatment
- hair should be clipped and all crusty material removed from affected areas prior to treatment
- selamectin has label claim for dogs - up to 2 doses required
- moxidectin in Advantage-Multi highly effective
- large animals – various endectocides have activity
and label claim against sarcoptic mange mites - older treatment - amitraz provides good control after a single dermal application – note toxicity to humans
Demodex spp.
(follicle mite or demodectic mange mite)
Demodex spp.; general; where do they infect, what do they cause, hosts
- infect hair follicles, sebaceous and apocrine glands
- cause demodectic mange or demodicosis
- many species infected with their own particular species of follicle mite
Demodex spp.; Morphology
- adults elongate, wormlike with stubby legs
Demodex spp.; Life Cycle
- mites are found on normal skin
- all stages on host within or at the mouth of hair follicles
- transmission by direct contact
Demodex spp.; Pathogenesis – Cattle/Goats
- Uncommon to rare
- Pinhead to egg-sized nodules
- Nodules filled with pus and mites – no need to deep scrape for diagnosis
Demodex canis
(canine follicle mite or demodectic mange mite)
Demodex canis; Pathogenesis - Dogs
mites are found on normal skin, therefore the pathogenesis is not fully understood
two general forms of the disease:
1) localized demodicosis, related to stress and possibly hereditary predisposition
2) generalized demodicosis
a) juvenile onset
b) adult onset
Demodex canis; Lesions and Clinical Signs - Dogs
- localized demodicosis - few small lesions with some hair loss and scaling (heal spontaneously)
- generalized demodicosis - generalized scaling, alopecia and erythema (“red mange”)
- follicle rupture leads to major secondary disease that may give rise to systemic clinical signs
- pododermatitis - severe lesions restricted to feet
Demodex canis; Diagnosis
- In dogs - deep skin scrapings with scapel performed at the edge of a lesion - examine microscopically – the root of plucked hairs from the edge of a lesion can also be examined for mites
- detritus from a scraping may be digested using 5% potassium hydroxide (near boil)
- In cattle/goats – express and examine contents of nodules
- mites may be mounted in Berlese solution
Demodex canis; Treatments - Dogs
- localized demodicosis - generally heal spontaneously, may use rotenone topically
- generalized demodicosis
- amitraz (Mitaban) is effective BUT treatments can be long and frustrating
- moxidectin in Advantage-Multi highly effective - ivermectin (off-label)
Otodectes cynotis
(ear mite)
Otodectes cynotis; general; where are they found, movement, host
- found in ear canal and adjacent skin
- actively move
- entire life history on single host
Otodectes cynotis; Morphology
- white oval mite with long legs extending past the body
- short, unsegmented pretarsi with a large sucker
Otodectes cynotis; Life Cycle, transmission
- egg to adult - 2 or 3 weeks
- transmission by direct contact
Otodectes cynotis; Pathogenesis/Lesions/Clinical Signs
- dermatitis and pruritis result from reactions to mechanical damage and secretions
- scratching and shaking of head
- dark exudate from ear
- mites can move out of ear and be found elsewhere
Otodectes cynotis; Treatment
- clean out debris from ears, particularly dried exudate, thoroughly
- instill topical acaracide into ear canal (rotenone, methyl phthalate, thiabendazole, milbemycin)
- selamectin has label claim for treatment and control of ear mites of cats and dogs
- moxidectin in Advantage-Multi has label claim and is highly effective
Cheyletiella spp.
(fur mite)
Cheyletiella spp.; Morphology
- larger, more robust mite (“walking dandruff”)
- legs long and extend beyond body margin
- large palps (“fifth pair of legs” – see arrows)
- comb-like structures on the ends of each leg
Cheyletiella spp.; Life Cycle
- mites tunnel into keratin layer of skin and feed on epidermal debris
- transmission by direct contact
Cheyletiella spp.; Pathogenesis/Lesions/Clinical Signs
- dorsal seborrhea, generally non-pruritic
- usually seen in younger dogs; these animals will usually have many mites
Chorioptes spp.
(mange mite of ruminants and horses)
Chorioptes spp.; Morphology
- Oval and up to 0.5 mm
- Long legs
- Short unsegmented pedicels with large suckers
Chorioptes spp.; Pathogenesis/Lesions/Clinical Signs
- mites feed at surface
- small early lesions that may coalesce
- cattle - most frequent with animals that are housed
- more common in the winter and often spontaneously disappears in the summer
– may be pruritic – animal may damage hide - sheep, legs or scrotal area - lesions not common
- horses, lesions more extensive with pruritus - animals may stomp and rub.
Psoroptes spp.
(scab mites)
Psoroptes spp.; Morphology
*Oval and up to 0.6 mm
* Long legs
* Long segmented pedicels with small suckers
Psoroptes spp.; Pathogenesis/Lesions/Clinical Signs
- mites by piercing the skin
- Inflammation and hypersensitivity
- red papules at sites of bites followed by skin thickening
- intense puritis produces self-inflicted alopecia
- serious but easily treated (no longer reportable)
