Diagnostic update - Demodicosis
Diagnosis and treatment of demodicosis in dogs and cats;
Clinical consensus guidelines of the World Association for Veterinary Dermatology
Mueller et.al (2020) generated the following consensus statements for canine and feline demodicosis:1
Consensus Statement 1: In young dogs with generalised demodicosis a temporary immune alteration most likely plays an important role in the pathogenesis. In older dogs, the disease may be associated with an immunosuppressive condition or treatment. However, other hitherto unknown factors also may play a role. In cats, demodicosis is usually associated with other diseases, with the exception of the contagious Demodex gatoi that can also affect otherwise healthy cats.
Consensus Statement 2: In young dogs, demodicosis has a genetic basis and most likely multiple genes are involved.
Consensus Statement 3: In dogs, two Demodex species occur, the shorter D. canis and the longer D. injai. In cats, the shorter D. gatoi has a more regional occurrence and different clinical signs than the classical D. cati.
Consensus Statement 4: Demodicosis in dogs is characterised by alopecia and comedones, follicular casts, papules and pustules. In more severely affected dogs crusting with secondary bacterial infections and systemic signs may develop. Dogs with demodicosis due to D. canis also can exhibit pruritus, especially when secondary infection is present. Demodex injai occurs more often in terrier breeds and additionally causes excessive greasiness. In cats, D. cati shows similar clinical signs, whereas by contrast infestations with the contagious D. gatoi often lead to truncal pruritus.
Consensus Statement 5 : Deep skin scrapings (currently the diagnostic method of choice), trichograms, tape strips and examinations of exudate may be useful in identifying Demodex mites. More than one mite on any given test is an indication of clinically relevant demodicosis.
Consensus Statement 6: Dogs with generalised demodicosis and their parents should not be bred.
Consensus Statement 7: Treatment for generalised demodicosis should be monitored clinically and microscopically every month until the second negative skin scraping. Miticidal therapy should be continued four weeks beyond the second set of negative monthly scrapings to decrease the risk of a disease recurrence.
It is generally recommended to continue miticidal therapy all year round, even after the resolution of demodicosis for routine flea and tick prophylaxis.
Consensus Statement 8: In dogs with demodicosis, systemic antibiotics will typically not be needed and topical antibacterial therapy combined with good miticidal agents will be sufficient unless severe bacterial infection is present.
Consensus statement 9 has been intentionally omitted as weekly Amitraz rinses are not licensed for use in Australia.
Consensus Statement 10: Oral ivermectin at 0.3–0.6 mg/kg daily, moxidectin at 0.3–0.5 mg/kg daily, milbemycin oxime at 1.0–2.0 mg/kg daily and doramectin injected subcutaneously every week at 0.6 mg/kg are effective therapies for canine demodicosis, but an initial gradual dose increase is recommended for systemic moxidectin and ivermectin to identify dogs sensitive to toxicosis induced by those macrocyclic lactones. Topical moxidectin/imidacloprid (Advocate) should be considered for mild-moderate cases of canine demodicosis.
Ivermectin is not recommended in GP clinics anymore since the launch of isoxazolines which are much safer and more effective treatment options for demodicosis.
Consensus Statement 11: A number of studies have evaluated the efficacy of isoxazolines for canine demodicosis in pet dogs. The published data are very encouraging and make this drug class an excellent treatment option for dogs with demodicosis.
Consensus statement 12 has been omitted as lime sulphur dips are not licensed for use in Australia.
Isoxazolines available in Australia:
Nexgard ® (afoxolaner) – beef flavour chew q 30 days
Simparica ® (sarolaner) – liver flavour chew q 30 days
Bravecto ® (fluralaner) – hydrolysed pork flavour chew (3 month duration) or topical fluralaner (6 month duration for dogs, 3 months for cats)
A note about food trials; it is important to consider the flavouring in these products for those dogs who are undertaking elimination diets or sequential dietary rechallenges. These proteins may not be novel and thus can affect the results/outcome of the diet trial. An alternative to oral chews is topical fluralaner, this can also be used for those dogs and cats with adverse cutaneous food reactions to certain proteins such as beef or pork.
Consensus guidelines are available on the World Association for Veterinary Dermatology website. These are a fantastic source of free, relevant information that is constantly reviewed and updated by specialist dermatologists. Other consensus statements can be found here;
https://wavd.org/continuing-education/consensus-guidelines/
References
Mueller, R. S., Rosenkrantz, W., Bensignor, E., Karaś‐Tęcza, J., Paterson, T., & Shipstone, M. A. (2020). Diagnosis and treatment of demodicosis in dogs and cats: Clinical consensus guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology, 31(1), 5-27. picin is a potent inducer of cytochrome P450.
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