22. Ectoparasitoses (scabies, fleas, lice) & other ectoparasites of dogs & cats

What are examples of mites affecting dogs and cats?

1. Sarcoptes scabiei var. canis

2. Notoedres cati

3. Demodex spp.

4. Otodectes cynotis

5. Cheyletiella spp.

6. Neotrombicula autumnalis

What is the causative agent of sarcoptic mange in dogs?

Sarcoptes scabiei var. canis

Where does Sarcoptes scabiei var. canis locate on the host?

Burrowing mite. Stratum corneum of epidermis, of head, neck, ears, ventral abdomen, elbow, hocks.

How is Sarcoptes scabiei var. canis transmitted?

Direct contact.

What is the life cycle of Sarcoptes?

Entirely on dog, complete LC takes 2-3 weeks. Female burrows into epidermis, lays eggs. Adult mite lives for 4-5 weeks on host, but can survive in cold/humid environment for 3 weeks re-infection.

What is the pathogenesis of Sarcoptes?

Skin changes triggered by allergic reactions to mite antigens. Changes starts on ears & head, spreading to chest, abdomen & legs

What are the clinical signs of sarcoptic mange?

1. Itching, intense pruritus, erythematous papules, crusted papules, skin damage from scratching & rubbing, alopecia & secondary infections (bacteria, yeast).

2. Classic form: incubation period: 3 weeks. intense pruritus w/ + pinnal pedal scratch. Urticarial lesions. secondary lesions, erosions, crusts, lichenification & hyperpigmentation.

3. Localised form: erythematous, papular, crusting lesions, sometimes excoriations - restricted to pinna margins or lateral elbows

4. Juvenile form: mild form seen in young dogs, mild pruritus, truncal scaling, sometimes pyotraumatic dermatitis

5. Systemic signs: anorexia, pyrexia, weight loss, polyuria-polydipsia (associated w/ immune-mediated glomerulonephritis)

   

How is sarcoptic mange diagnosed?

History, clinical signs, mite detection in deep skin scrapings, pinnal pedal reflex.

What are differential diagnoses of Sarcoptes infestation?

Allergy (atopy, food, fleas), Cheyletiellosis, Otodectes cyanotis, pediculosis, autoimmune skin disease

What is the treatment for sarcoptic mange?

1. Clip hair, wash w/ antiseborrheic shampoo to remove dirt & crusts. Only after this can one start w/ topical treatments.

2. Topical: Selamectin & moxidectin: spot on. Monthly intervals for 2-3 months. Appears to be safe even for ivermectin-sensitive collies.

3. Systemic: Ivermectin (S.C injection) – NOT IN COLLIES!.

4. Systemic corticosteroids first week for pruritus.

What is the causative agent of notoedric mange in cats?

Notoedres cati

Where does Notoedres cati locate on the host?

Burrowing mite. Stratum corneum of epidermis, of face, neck, especially ears.

What are the clinical signs of notoedric mange?

Severe itching, lesions on tip of ear, thickening of the skin with formation of wrinkles and crusts.

How is notoedric mange diagnosed?

Clinical signs, skin scrapings.

What is the treatment for notoedric mange?

Lime-sulfur dips, selamectin, ivermectin. (NOT AMITRAZ)

What are the causative agents of demodicosis?

Dogs: Demodex canis, injai, cornei

Cats: Demodex cati, gatoi

Where does Demodex spp. locate on the host?

Burrowing mite. Hair follicles and sebaceous glands.

How is demodicosis transmitted?

From mother to offspring during nursing. Not contagious; part of normal microfauna. Immunosuppression → overgrowth → demodicosis

What are the clinical signs of demodicosis?

1. Localised: erythema, alopecia, scaling, NO PRURITUS

2. Generalised: severe disease with secondary bacterial infection, pododermatitis, lymphadenopathy, lethargy, fever, deep pyoderma

3. Otodemodicosis: erythematous, ceruminous otitis.

How is demodicosis diagnosed?

History, clinical signs, deep skin scrapings from comedones/predilection site (KOH).

What is the treatment for demodicosis?

Juvenile: no treatment. Recovers spontaneously in 1 year

Localised: spontaneous recovery. Benzoyl peroxide shampoo.

Generalised: amitraz bath, ivermectin, moxidectin, fluralaner, antibiotics. Treat underlying problem

What is the causative agent of ear mites?

Otodectes cynotis

Which species are affected by Otodectes cynotis?

Dog and cats (50:50). Not species specific

Where does Otodectes cynotis locate on the host?

Non-burrowing mite. Ear canal, outer ear.

How is Otodectes cynotis transmitted?

Direct contact. Highly contagious

What is the pathogenesis of Otodectes cynotis?

Local allergic reaction. Purulent inflammation & discharge of external ear, may perforate tympanic membrane

What are the clinical signs of Otodectes cynotis infestation?

Otitis externa: ceruminous discharge from ear canal - coffee ground. Discharge can become purulent if 2nd infection, pruritus variable. Othaematoma can occur as a result of head shaking.

Ectopic infestation: usually seen in cats, tend to occur in neck, rump & tail, can be asymptomatic or pruritic. Lesions present as papular crusted eruptions.

How is Otodectes cynotis diagnosed?

Detection with otoscope, ear-smear, skin scrapings, tape impressions.

What is the treatment for Otodectes cynotis?

Selamectin, moxidectin, amitraz, thiabendazole/acaricide ear drops.

Must treat for 3-4 weeks to cover the life cycle (treatment does not affect eggs)

How is Otodectes cynotis infestation prevented?

Cleaning ears: salicylic alcohol, borax, oil etc

What are the causative agents of Cheyletiellosis?

Cheyletiella yasguri (dogs), Cheyletiella blakei (cats). Zoonotic

How is Cheyletiellosis transmitted?

Direct and indirect contact. Highly contagious

Where is Cheyletiella found?

Non-burrowing mite. On the surface of epidermis. Walks very quickly, has hooks on palps to hold onto the surface of skin, piercing & chewing mouth

What is the life cycle of Cheyletiella?

Entire LC on host (3w). Eggs are contained in a cocoon-like structure that is attached to hair.

What is the pathogenesis of Cheyletiella?

Cheyletiella is the most common cause of chronic eczema in dogs & cats. Hair loss, papules

What are the clinical signs of Cheyletiellosis?

Pruritus, mild to severe dandruff, scaling, dorsal crusting. Walking dandruff.

How is Cheyletiellosis diagnosed?

Adhesive tape (transparent), superficial skin scraping, flea combing.

What is the treatment for Cheyletiellosis?

Weekly baths to remove crusts → Lime sulphur baths, fipronil, ivermectin, amitraz.

Treat environment → adult mites can survive days-weeks off the host

What is the causative agent of Chiggers?

Neotrombicula autumnalis

Where is Neotrombicula found?

Non-burrowing mite. Area between toes, inguinal area, bridge of nose, ears, eye ring

When are Neotrombicula infestations more common?

August-September

What is the pathogenesis of Neotrombicula infestations?

Release cytolytic enzymes which when come in contact with muscles it causes the destruction of intersegmental muscles

What are the clinical signs of Chiggers infestation?

Skin reactions, irritation, persistent itching, erythema, hives, blisters, crusts, secondary alopecia, convulsions, epileptic seizures.

What bacteria is Neotrombicula autumnalis a vector for?

1. Rickettsia tsutsugamushi

2. Borrelia genospecies

3. Anaplasma phagocytopillium

4. Ehrlichia phagocytophila

What is the diagnosis for Neotrombicula?

Not easy, anamnesis, CS, microscopy (red larvae)

What is the treatment for Chiggers?

Cats: fipronil, selamectin

Dogs: permethrin-pyriproxyfen combination.

How is Neotrombicula infestation prevented?

Avoid areas and season

What are the most frequent external parasites of companion animals worldwide?

Fleas.

What are examples of zoonotic diseases carried by fleas?

Dipylidium caninum, Yersinia pestis, etc.

What is the pathogenesis of fleas?

Reactions of host to flea bites are due to salivary components of fleas: histamine, enzymes, etc. Repeated flea bites can cause flea allergy dermatitis (FAD). They also transmit pathogens.

What are examples of species of fleas and their host species?

1. Ctenocephalides canis → dog, human

2. Ctenocephalides felis → cat, human

3. Pulex irritans → humans, domestic mammals

What is the general life cycle of fleas?

Eggs laid on host ⤍ fall off ⤍ larva ⤍ pupate ⤍ adult can live months without bloodmeal, but aggressively wants & looks for food

What are the clinical signs of flea infestation?

Skin reactions (pruritus, erythema, papules), flea allergy dermatitis (FAD), miliary dermatitis (cats).

What are clinical signs of flea allergy dermatitis (FAD)?

Acute phase: itching, erythema & papules

Chronic phase: crusty, purulent dermatitis, bacterial folliculitis, 2nd seborrhoea & alopecia.

How are fleas diagnosed?

CS, detection of adult fleas or flea faeces on the animal & combing. 
Flea faeces are reddish brown particles that when wetted give off a red brown discoloration

What is the treatment for fleas?

Selamectin, imidacloprid, fipronil, fluralaner, deworming. Treat animal and environment.

What are the causative agents of lice infestation?

Mallophage (chewing lice): Trichodectes canis, Felicola subrostrata

Anoplura (sucking lice): Linognathus setosus (cats are not affected by sucking lice)

How are lice transmitted?

Direct or indirect contact. Eggs of lice are found glued to hair or feathers, & whole life cycle takes 2-3 weeks to complete

What are the clinical signs of lice infestation?

Self-trauma causing hair loss and abrasions, itching, scratching, matted fur, anaemia (sucking lice).

How is lice infestation diagnosed?

Visualisation of lice.

What is the treatment for lice infestation?

Lime sulphur shampoo (repeat 2x at 2 week interval), fipronil, ivermectin, organophosphates, permethrin (NOT IN CATS).

What are some examples of hard ticks?

Ixodes ricinus, Haemaphysalis, Rhipicephalus sanguineus, Amblyomma, Dermacentor reticulatus.

What are some examples of soft ticks?

Otobius megnini.

Where does the life cycle of the tick occur?

Partly on host & environment. Must feed on blood to moult.

What is the pathogenesis caused by ticks?

1. Cause skin disease (dermatitis, inflammation, swelling, ulceration, itching), allergy, annoying, anaemia.

2. Vector of pathogens! Babesia, Hepatozoon, lyme/Borrelia, Anaplasmosis, Cytauxzoon

What are the clinical signs of tick infestation?

Skin disease (dermatitis, inflammation, swelling, ulceration, itching), allergy, anaemia

How are ticks prevented?

Acaricides (spot-on, oral tablet): Imidacloprid, organophosphates, Fluralaner

What are the clinical signs of fly infestation (myiasis)?

Ulcers with tissue necrosis, acetone smell, lesions around nose, eyes, mouth, anus, genitalia, neglected wounds.

What is an example of a species causing myiasis?

Chryosoma bezziana (Old world screwworm)

What is the pathogenesis of myiasis?

Maggots from dipterous flies ingesting tissue

Vector of pathogens → Thelazia (eye-worm)

What are clinical signs of myiasis?

Ulcers with tissue necrosis, acetone smell.

​​Lesions affect skin around nose, eyes, mouth, anus & genitalia, as well as neglected wounds.

Typical appearance is of punched out ulcers with tissue necrosis containing larvae.

Maggots will orientate vertically w/i wounds to maximise use of space

What is the treatment for fly infestation (myiasis)?

Antibacterial wash, surgical debridement, insecticidal wash or spray, systemic larvicidal drugs, antibiotics.

Which antiparasitics should not be used in cats?

Amitraz, permethrin