Sarcoptes, Otodectes & Demodex Dr Lee Strapp BVetMed MRCVS Veterinary Scientific Liaison Bayer Animal Health
Overview • Sarcoptes, Otodectes, Demodex • Three different mites, all commonly encountered • Obligate parasites - entire life cycle on host • Skin disease termed mange: – sarcoptic, otodectic or demodectic
Sarcoptes
Introduction • Sarcoptes scabiei var. canis • Burrowing mite, found in the lower stratum corneum of the epidermis • Relatively common in dogs, foxes, other canidae • Very rare in cats (host specific Notoedres cati ) • Zoonotic; can infest humans • Often referred to as Sarcoptic mange / fox mange • Known as scabies in human medicine • Highly contagious – whole household
Life Cycle • Exclusively on host • 2 to 3 weeks • Mating on surface • Egg laying in burrows • Transmission; close contact 1 Egg 4 Tritonymph 2 Larva 5 Adult 3 Protonymph
Clinical Signs • Pruritus (often intense) • Alopecia • Erythema • Papules • Crust • Excoriations • Secondary pyoderma • Pinna-pedal reflex often present • Predisposed sites; ears, muzzle & elbows
Clinical Lesions
Clinical Signs (Chronic) • Ongoing pruritus • Extensive self trauma • Scale • Hyperpigmentation • Lichenification • Untreated can spread to whole body • Systemic signs may be seen – Lethargy / malaise / inappetance • Histopathology – Chronic inflamm. / hyperkeratosis / parakeratosis
Typical Distribution of Lesions • Head – Periocular – Pinnal margin • Ventral abdomen • Chest • Legs – esp. elbows
Pinna-Pedal Reflex • Rub pinnal margins – frantic scratching • Common – BUT not always seen
Sarcoptic Mange in a Puppy
Identification • Sarcoptes scabiei mites are rotund, ventrally flattened and dorsally convex, with short legs • The dorsum is covered in spines and there is a terminal anus
Diagnosis 1 • Presumptive diagnosis is often made on the basis of history & clinical signs – Dermatitis affecting dog & in contact dogs +/- humans – Nature and distribution of cutaneous lesions – Positive pinna-pedal reflex highly suggestive – Pruritus minimally responsive to steroids • Similarity with a number of differential diagnoses, aim for a laboratory diagnosis
Diagnosis 2 • Confirmatory diagnosis by skin scrapings • As many as possible; edges of lesions, not from open wounds or chronically inflamed excoriations • Preferred locations are those covered in visible raised yellowish crusts and papules • Sites of predeliction; edges of ears, elbows and limbs especially around tarsal joint • Mites, mite eggs, mite faeces • Low sensitivity ~25% confirmed by scrapes
Sarcoptes scabiei microscopy • 10% potassium hydroxide (KOH) solution can be added to the collected material and then gently warmed to help clear the debris to reveal the mites
Sarcoptes egg
Diagnosis 3 • Serological testing – commercial ELISA tests (demonstration of anti Sarcoptes scabiei var canis IgG) sensitivity up to 90% – False negatives, as seroconversion can take ~5 weeks – Positive results DO NOT indicate active infestation but do indicate prior exposure – Time taken to be seronegative - several months + – Do not use to declare failure of treatment • Histology – not usually conclusive, unless find mites themselves by chance
Treatment • Systemic acaricides – 10% imidacloprid / 2.5% moxidectin spot-on 0.1ml/kg, twice 4 weeks apart – Selamectin spot-on 6-12mg/kg, twice 30 days apart • Topical acaricides – Amitraz, weekly sponge on • Systemic isoxazolines – Sarolaner, twice at monthly intervals
Sarcoptic Mange – Response To Treatment Before treatment
Sarcoptic Mange – Response To Treatment 22 days after initial treatment
Sarcoptic Mange – Response To Treatment 50 days after initial treatment
Efficacy of Treatments • “Both products were highly effective against sarcoptic mange with a parasitological cure rate on Day 56 of 100%.” • “…dramatic reduction in the clinical signs associated with sarcoptic mange from the first application.” • Must treat in-contact animals! Australian Veterinary Journal – Vol. 84, February 2006’ Fourie et al.
Sarcoptic Mange in a Human • Severe clinical cases in humans are frequently associated with host adapted S. scabiei var. hominis
Otodectes
Introduction • Otodectes cynotis is the most common mange mite of cats and dogs in the world • Over 50% of otitis externa cases in dogs and 85% in cats involve infestations with Otodectes • The mites do not burrow; they live on the surface of the skin of the outer ear canal • They feed, causing irritation and the canal becomes full of cerumen, blood & mite faeces
Life Cycle & Transmission • Entire life cycle on host; complete in ~3 weeks • Eggs hatch into larval ear mites in ~4 days • One larval & two nymphal stages then adult • Transmission usually by direct contact: – especially from infested dams to their young – also from dogs to cats and vice versa • Transmission through cerumen expelled from ear during scratching & head shaking is rare • Large proportion of cats & dogs harbour a small population of mites
Clinical Signs • Brown waxy discharge in external ear canal • Ear mites may be seen • Pinnae & ear canal erythema • Mild to severe pruritus – physical presence of mites & mite saliva is an irritant • +/- Ulceration • Signs of secondary trauma – Excoriation & wet eczema • Head shaking +/- Aural haematoma – Tympanic membrane may be perforated » Torticollis / Circling / incoordination
Discharge from Otodectes
Diagnosis • Dark brown to black crumbly crusts or waxy deposits + pruritus highly suggestive • Visualisation of mites on direct otoscopic examination (BUT avoid light!) • To confirm diagnosis, ceruminous debris removed from ear canal and examined microscopically for mites +/- eggs
Otodectes on Microscopy
Treatment • Ear cleaning products remove ceruminous debris • Ear drops applied directly into the ear canal usually twice daily for several days – repeat course 7-10 days later is required • Topical spot-ons incorporating systemic active ingredients, such as moxidectin or selamectin • In some clinical cases, anti-inflammatory medications are used to ease secondary signs
Advocate Treatment • ‘Do not apply directly to the ear canal’ • ‘Examination 30 days after treatment is recommended as some animals may require a second treatment’ • Efficacy 98-99% • Treat in-contacts
Demodex
Introduction • Demodex canis is a common mite of dogs • Low numbers - normal part of cutaneous fauna • Other Demodex species are very rare: – longer body mite Demodex injai (greasy skin, Terriers) – shorter body mite Demodex sp. (cornei) • Demodex cati & Demodex gatoi of cats are extremely rare (often associated with FeLV/FIV) – NB: D. gatoi is unlike all the other Demodex species, being transmissable and causing a sarcoptes like intense pruritus
Transmission • Demodicosis is not considered a contagious disease; no horizontal transmission (except D. gatoi ) • Mites are only transmitted from the bitch to nursing puppies – Stillborn pups from infected dams free of mites – Puppies delivered by Caesarean do not have mites if not allowed contact with the dam • Tendency to develop clinical disease, demodicosis, influenced by: – genetic T-cell defect (hereditary) – Immunosuppression due to debilitating disease – Immunosuppressive medications (e.g. steroids)
Demodicosis Predisposing Factors • As well as immunosuppression from disease or medications, other predisposing factors: – Short hair – Poor nutrition – Stress – Oestrus – Endoparasites – Pyoderma
Life Cycle • Exclusively on host • Fusiform eggs (lemon shaped) • 6 legged larvae (2 stages) • 8 legged nymphs (2 stages) • Adults • 18-24 days
Clinical Signs 1 • Erythema • Papules • Comedones • Alopecia • Scaling • Hyperpigmentation • Pruritus not usually a feature unless secondary factors
Clinical Signs 2 • Secondary pustule formation • Severe disease; follicles rupture = furunculosis with deep lesions & crusting • Lesions anywhere on body; face & feet most commonly affected • Generalised cases may also show depression, lethargy, lymphadenopathy
Human Demodicosis Canine Demodicosis
Diagnosis • Deep skin scrapings +/- trichograms • A small area of skin (1-2 cm 2 ) scraped in direction of hair growth until capillary bleeding – A blade covered with liquid paraffin is used • Follicular papules or pustules are good sites for scraping • Squeezing skin helps push mites out of follicles
Demodex canis on microscopy
Deomodex in Skin Scrapings • Demodex mites are a normal part of cutaneous fauna so occasional mites can be found normally – extremely rare to see more than one Demodex canis mite in a dog not affected by demodicosis • Note the site of scraping & relative numbers of adults, larvae, nymphs & eggs per field • Assessment of response to therapy relies on comparison of such numbers • Scrapings ideally repeated at the same sites monthly
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