Parasitology - Mites Flashcards
How big are mites?
They’re microscopic. Less than 0.3 mm.
Can you kill them with insecticides?
No, like ticks, they’re not insects. They in the class Arachnida.
What is the condition caused by mites?
Mange
How do their life cycles differ from ticks in terms of where they spend their time?
Ticks spend most of their time on the ground, even if they’re 1,2 & 3-host ticks.
Mites spend most of their time on the host.
How are mites classified?
By where they’re located on the host.
Burrowing mites & Surface mites.
Most species of veterinary importance are parasidic.
What are the three main genera of BURROWING MITES?
Sarcoptes
Knemidocoptes
Demodex
What conditions does Sarcoptes cause & in what species?
Sarcoptic mange in
PIGS: important condition (~35% harbour inapparent infections); ears commonest site of infection; transmission from sows to piglets during suckling & boars to gilts @ surface; adversely affects productivity
CATTLE: mostly in housed cattle, potentially most severe of cattle manges; notifiable in Canada & parts of US; lesions on neck & tail; adversely affects productivity
SHEEP: notifiable in UK (last case 30 yrs ago)
HORSES: notifiable in UK (2 cases since 1948); lesions spread from head, neck, shoulders to rest of body
DOGS: highly contagious, intense itching, edges of ears first affected, later muzzle, face & elbows (rest of body)
CATS: rare
How do you recognise an adult Sarcoptes mite?
- small, round - dorsal PEGS arranged in rows
& spines - terminal anus
How many legs do burrowing mites like Sarcoptes & Demodex have as adults and nymphs?
They have four pairs of legs as adults & nymphs and only three pairs as larvae.
What is the life cycle of the Sarcoptes scabiei?
~3 weeks:
Fertilised female creates tunnel in upper epidermis → lays eggs “in pocket” → feeds on liquid oozing from damaged tissues → eggs hatch in <1 week → larvae crawl to surface then burrow back into epidermis to form “moulting pockets” → moult to become nymphs → moult 2x to become adults
How is Sarcoptes diagnosed?
-
Skin scraping to expose
capillary blood -
add KOH & warm over
Bunsen burner - place coverslip on top
- ID X-section of mites on
epidermis
What are the clinical signs of sarcoptic mange?
- erythema w/ papulae
- scale, crust formation, alopecia
- intense pruritus (1 week), self-inflicted
trauma & scabs - wrinkling & thickening of skin
NB pigs & humans can have hypersensitivity reax w/i hours
Another burrowing-mite genus is Knemidocoptes. What species does this mite attack?
Poultry/wild birds
How is Knemidocoptes mite identified?
Usually you can figure out its a Knemitodcoptes mite if there’s mange on a bird.
You can also look under a microscope for a U-shaped chitinous bar behind its head, and a terminal anus.
What are the different species of knemidocoptes? What are the common names of the conditions they cause?
K. mutans
K. gallinae
(“depluming itch” - poultry)
K. pilae - (“scaly beak/face”- cage birds)
NB: Knemidocoptes is the only burrowing mite that affects birds.
(“scaly leg” - poultry)
What is the pathogenesis of Knemidocoptes mutans?
K. mutans causes scaly leg in poultry.
- mites burrow beneath leg scales causing them to loosen & rise giving a ragged appearance to legs & feet.
- Affected birds may have distorted feet &
claws & show signs of lameness.
What is the pathogenesis of Knemidocoptes gallinae, the cause of “depluming itch” in poultry?
- mites burrow into feather shafts which results in intense pain & irritation causing birds to pull out body feathers
- very painful
What is the pathogenesis of Knemidocoptes pilae, which causes scaly beak or scaly face in caged birds?
- mites attack bare or lightly feathered parts of beak, cere, face & body
- first see scaliness @ base of beak → spreads across face & sometimes body
- little priuritus
Demodex is another important burrowing mite. What is special about the way it looks under the microscope that helps you to ID it?
Demodex is cigar-shaped with four stumpy legs at anterior end.
What is the name of the condition caused by Demodex burrowing mites?
Demodecosis
There are two types of demodecosis caused by the burrowing mite, Demodex. What are they and how do they differ?
a) Squamous demodecosis - less serious, dry reax with alopecia, desquamation & skin thickening; absent/mod. pruritus
b) Pustular (or follicular) demodecosis - more serious, resulting from invasion by Staphylococci. Skin becomes wrinkled & thickened & contains numerous pustules that ooze serum, blood or pus; animals might be severely disfigured; severe pruritus associated with secondary infection.
Which species do Demodex burrowing mites attack?
Found on all domestic animals & humans, each having its own species.
We are concerned with dog infestation.
May cause severe skin disease.
How do dogs “catch” Demodex infestation aka demodecosis?
- transmitted by bitch → puppies during suckling; lesions seen first on muzzle, face & forelimbs
What are predisposing factors in dogs becoming infected by Demodex burrowing mites?
- family susceptibility - weak puppies
- immunosuppression - Demodex thought to cause cell-mediated immunodeficiency by suppressing normal T-cell response;
- immunosuppressants - corticosteroids
What is the Demodex life cycle?
3 weeks:
adult → egg → larvae → nymph → adult
Normally live as commensals in skin of most animals, spending their entire life cycle in hair follicles & sebaceous glands.
Mites can act as intermediate hosts for other types of parasites. Give two examples of parasites that use the Oribatid mites, which themselves are NOT parasitic.
Oribatid mites, though not parasitic themselves and are more like ticks that spend their time OFF hosts, are intermediate hosts for several nematode species that can become tapeworms in final mammalian hosts.
Anoplocephala - equid tapeworm
Moniezia - ruminant tapeworm
How do non-burrowing mites differ from burrowing mites in terms of behaviour and location on the host?
Non-burrowing, aka “surface” mites, live on the surface of the skin, some feeding on skin scales or tissue (a bit like chewing lice vs. blood-sucking lice), although some such blood too.
How do surface/non-burrowing mites differ in appearance to burrowing mites?
They are more oval in shape with long legs (pedicels) that are either segmented (Psoroptes) or non-segmented (Chorioptes). The pedicels have funnel-shaped or cup-shaped SUCKERS mounted on the ends.
See photo of Psoroptes.
What are the main species or genera of non-burrowing mites?
Psoroptes
Chorioptes
Otodectes
Cheyletiella
What is psoroptic mange and what is the pathogenesis? Which animals are affected?
Psoroptic mange is also known as “sheep scab”, but it also affects cattle, horses and rabbits.
Psoroptes ovis - sheep & cows
Ps. equi - horses
Ps. cuniculi - rabbits & horses
Pathogenesis:
- though NOT BURROWING, it is very active in keratin layer of skin & has mouthparts that abrade skin
- antigenic material in faeces → hypersensitivity reax → inflammation, serous exudation, dry yellow crust & scale formation → self-inflicted trauma (intense pruritus, rubbing off fleece)
- impaired productivity (poor live-weight gain)
How is Psoroptes transmitted in domestic animals?
- mites found mainly under
scabs or skin folds -
spread by direct transfer of
mites between sheepeg at
markets -
indirect spread possible eg.
contaminated troughs,
inanimate objects/fomites - different strains, non-
pathogenic found in ear
What is the life cycle of a Psoroptes mite?
Very short - only about 10 days
egg → larvae → nymph → adult
- female lays up to 100 eggs during her life of one month; spend all of time on host
- confined to surface of skin, the mites feed by siphoning up serous exudate
How can you tell the difference between Chorioptes and Psoroptes non-burrowing mites by morphology?
They are both oval with long legs/pedicels, but Psoroptes have segmented pedicels with suckers at the end, and Chorioptes have unsegmented pedicels. See pedicels photo.
Psoroptes mites are found on ruminants, horses and rabbits. Where are Chorioptes found?
They are a surface mite found on ruminants and horses.
They are all different strains of the same species,
Chorioptes bovis
What is the difference in pathogenicity between Psoroptes and Chorioptes surface mites?
Chorioptes are much less pathogenic than Psoroptes as mouthparts NOT adapted for piercing/abrading skin but for feeding on surface skin scales & other debris
What are the clinical signs of chorioptic mange on horses, especially shire horses, which tend to get it more?
Chorioptic mites induce crusty lesions & thickened skin below the knees & hocks.
Where would you find a species of Otodectes surface mite?
In the ears of cats or dogs.
Otododectes cynotis is the commonest mange mite of cats & dogs in the world.
Inhabitants of external ear.
Also found in fox & ferrett.
How does the life cycle of this surface mite differ from that of Psoroptes?
It’s the same except instead of 10 days, it’s three weeks.
egg → larvae → nymph → adult
- female legs up to 100 eggs during her life of one month.
- confined to surface of skin, the mites feed by siphoning up serous exudate.
What is the proper name of the condition in which the outer ear & ear canal are inflamed, and which is commonly caused in dogs by the surface mite of the Otodectes genus, Otodectes cynotis?
Otitis externa
How is otitis externa diagnosed in a dog?
Clinical signs of head-shaking & scratching, foetid waxy masses in ear canal & occasionally aural haematoma.
Can visualise mites with auroscope or swab.
How can you treat otitis externa in a dog or cat?
- ear drops w/ combo
acaricide, fungicide,
antibiotics, steroids, etc. - Selamectin is active against Otodectes (spot-on)
-
repeat in 10-14 days to kill
newly hatched - treat all in-contact animals
How does the appearance of the Cheyletiella surface mite differ from Psoroptes?
- waisted body
- claw-like palps at head end
- combs at end of each leg
See photo
Why are Cheyletiella surface mites important?
ZOONOTIC!
Mainly on cats & dogs but also found on rabbits & humans.
Highly contagious
What are the main species of the genus Cheyletiella and what animals do they affect?
- Cheyletiella yasguri* - dog
- C. blackei* - cat, and most often found in humans
- C. parasitivorax* - rabbits
How does the life cycle of Cheyletiella mites differ from that of Psoroptes?
It’s two weeks instead of 10 days.
egg → larvae → nymph → adult
- female legs up to 100 eggs during her life of one month
- Live in hair & fur, only visiting skin to feed on skin scales & other debris.
How is infection by Cheyletiella mites diagnosed?
Clinical signs eg excessive scurf
Brush scurf onto paper - when they present in large numbers, mites move among debris to present “walking dandruff”
What are the clnical signs of Cheyletiella mites and how does it spread?
Highly contagious though mild condition in animals
- very scaly dermatitis
- mites easily transferred to humans & can readily penetrate clothing causing more-severe condition ie., intense pruritus, vesicular/ pustular eruptions
What is the history of sheep-scab control in the UK?
Sheep scab is another name of Psoroptic mange caused by the non-burrowing Psoroptes mite, Ps. ovis.
Legislation to make sheep scab notifiable in UK was introduced due to high population turnover & mite pathogenicity.
1952 - eradicated.
1973 - reappeared.
1992 - deregulated due to large ↑ in cases and lack of compliance with compulsory dipping by sheep industry.
2010 - Defra re- introduced dipping in Scotland, where it’s now a notifiable disease.
Remains notifiable in Aus. & NZ where it has been long eradicated.
What is the common name for the Dermanyssus mite D. gallinae, that feasts on the blood of poultry?
Red mite - turns bright red after blood meal
How does the appearance of the non-burrowing red mite, Dermanyssus gallinae, differ from Psoroptes?
It’s spider-like, with long legs, it’s white or grey when it’s not had a blood meal (then it turns bright red), and it has hooks on its legs.
See photo.
What is different about the red mite’s life cycle from Psoroptes in terms of length & where the eggs are laid, and where they spend most of their lives?
The red mite is Dermanyssus gallinae, which affects chickens.
The cycle is only one week compared with 10 days in Psoroptes.
The eggs are not laid on host but in crevices in the chicken house.
They spend most of their life OFF the hosts, and visit only at night to feed.
They can survive MONTHS without feeding.
How is the feeding behaviour of red mites different from Psoroptes and Chorioptes?
Dermanyssus gallinae is a blood sucker, more like a tick than a mite. Mites like Psoroptes, which has abrasive mouth parts, still feed off exudate and tissue debris. Choroptes don’t have rasping mouth parts so only feed on scales and skin debris.
D. gallinae actually feed on blood and become engorged, more like ticks. And they feed at night, visiting the hosts (chickens) only to feed. They spend most of their lives off the host.
Why is the Neotrombicula surface mite important?
It has a parasitic larval stage that can attack humans, causing hypersensitivty reaction - nymph and adult only live in soil.
Unlike all other mites, Neotrombicula can be found on every species.
What are the distinguishing features of Neotrombicula morphology?
Bright orange & hairy with only six legs.
See photo.
Which mites – burrowing and non-burrowing – can be found on humans?
Sarcoptes
Demodex
Cheyletiella
Dermanyssus (this is the chicken one - rarely)
Neotrombicula
