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Veterinary Forum April 2009 (Vol 26, No 4)

Parasite 101— Canine and Feline Otoacariasis: Ear Mites Revisited

by Byron Blagburn, MS, PhD

    The ear mite, Otodectes cynotis, is a common and highly contagious cause of otitis externa, also called otoacariasis and ear canker, in cats and dogs.1-3 Ear mites most often infest cats, particularly kittens, but also can infest dogs. Some reports suggest that ear mite infestation has a seasonal predilection and occurs more often during the summer,4,5 whereas others specify no seasonal predilection.6 Symptomatic otoacariasis appears to occur more often in young dogs and dogs with pendulous ears.5,6

    Although the common name for O. cynotis implies that the organism is restricted to the ears, these mites may colonize the hair coat, particularly on the side of the pet's face, the pinna, the rump, and the tail. Adult pets, especially cats, can harbor mites but remain asymptomatic carriers.

    Ear mites are particularly hardy and can survive off the host for at least 12 days.7 O. cynotis can infest humans and is, therefore, a potentially zoonotic ectoparasite.8-10

    Characteristics of ear mites

    O. cynotisis a psoroptiform mite related to Chorioptes organisms, Psoroptes ovis, and P. cuniculi.11 P. cuniculi is the cause of otitis externa, or ear canker, in rabbits and other mammals.

    Unlike the scabies mites Sarcoptes scabiei and Notoedres cati, ear mites are nonburrowing and feed on surface cells, debris, and inflammatory exudates. Adult ear mites are oval, measure 0.3 to 0.5 mm long, and have four pairs of legs. All legs of male ear mites extend beyond the outer margin of the body; the fourth pair of legs of female mites is rudimentary (Figure 1). All legs of male mites and the first two pairs of legs of female mites contain cup-shaped suckers on short, unsegmented pedicles (Figure 1).

    The entire life cycle takes place in the ears and/or hair coat of dogs and cats. Mites do not develop in the environment, although they are known to survive off the host for several days to weeks.7 Stages in the life cycle include eggs, six-legged larvae, eight-legged proto­nymphs and deutonymphs, and eight-legged adults. Complete development from egg to adult takes about 3 weeks. Only the adult mites are sexually distinguishable. Transmission from host to host is by direct contact, particularly from dams or queens to puppies or kittens, respectively. Transmission by way of ear wax or on the claws of infested pets can occur but seems to be rare. The lifespan of mites is approximately 2 months.12

    Clinical disease

    Ear mites cause a local inflammatory reaction in the external ear canal consisting of cerumen, blood, mite feces, and tissue debris. The dark brown to black, crusty exudate resembles "coffee grounds" with a waxy consistency. Pruritus is often marked and can lead to self-inflicted pyotraumatic dermatitis (hot spots) on the head, the pinna, the side of the face or neck, or the external ear canal. Inflammation and subsequent lesions can result from just two or three mites,13 probably because of hypersensitivity. The exudate can become purulent if secondary bacterial otitis develops. Aural hematomas may result from constant head-shaking, especially in dogs with pendulous ears.5 Ectopic infestations of the head, neck, rump, and tail can occur, particularly in cats, and may result in papular dermatitis with crusted eruptions.2

    A recent report described self-mutilation of the head and neck, interdigital erythema, and erythematous nail beds in a cat infested with O. cynotis.14 Mites were not present in ear swabs but were recovered in skin scrapings from the head and nail beds. It is believed that severe inflammation in the ears may create an environment that is not conducive to mite survival.13 Inflammation may cause the mites to abandon the ear for other somatic locations and result in negative ear examinations, as described in this report. Older dogs or cats are more likely to be infested with ear mites and remain asymptomatic.13

    Pruritus induced by ear mites may be caused by hypersensitivity to antigenic components of mite saliva.3,13 Antibodies produced against ear mites also are known to cross-react with antigens produced by the house dust mites Dermatophagoides farinae and D. pteronyssinus. Therefore, on intradermal skin tests, ear mite-infested dogs and cats may react positively to antigens from house dust mites, resulting in an incorrect diagnosis of atopic dermatitis or asthma.14-16

    Diagnosis and treatment

    A diagnosis of otoacariasis is based on history, clinical signs, and recovery of mites. Mites may be observed on ear swabs or in exudates from swabs examined in liquid paraffin or potassium hydroxide. Mites also may be observed using either an optical or video otoscope. Ectopic infestations can be confirmed by superficial skin scrapings or by sampling the hair coat or lesions using acetate tape. A positive pinnal-pedal reflex is often present in cats but not in dogs.1,17

    Numerous labeled products are available for the treatment of otoacariasis in dogs and cats (Table 1).

    Some products also may be used off-label.1,18 For example, ivermectin (1% injectable) can be administered at 0.3 mg/kg PO q7days for three to four treatments or at 0.3 mg/kg SC q10-14days for three treatments. This same formulation can be diluted one part ivermectin to nine parts propylene glycol. Two to four drops of this solution can be applied to each ear q24h for 3 to 4 weeks. Another off-label use is 10% fipronil solution (Frontline, Frontline Plus; Merial), which has been used on dogs and cats at the rate of two drops per ear, once or twice, 2 to 4 weeks apart. Likewise, additional off-label use of Otomax (Intervet/Schering-Plough Animal Health) and of Tresaderm (Merial) may eliminate ear mites, and ingredients contained in both products can reduce inflammation and are effective against secondary bacterial and yeast infections.

    Some sources advocate cleaning the patient's ears with a ceruminolytic product before administering intra-aural drops.2 The author favors topical monthly broad-spectrum products that are applied to the skin surface because they have the advantage of eliminating auricular and ectopic ear mite infestations and other ectoparasites, such as fleas or scabies mites (Sarcoptes spp). In addition, continued monthly use of broad-spectrum products can help prevent recurrence of otoacariasis.

    For more information:

    Readers can view ear mites in a short-streaming digital video prepared by Dr. Louis Gotthelf using a MedRx video otoscope at mms://cvm-vid.vetmed.auburn.edu/blagburn/earmites.wmv.

    Dr. Blagburn reported no potential conflict of interest relevant to this article. The CAPC receives financial support from pharmaceutical companies.

    1. Medleau L, Hnilica KA. Small Animal Dermatology, ed 2. St. Louis, Mo.: Saunders/Elsevier; 2006.

    2. Paterson S. Parasitic skin diseases. In: Manual of Skin Diseases of the Dog and Cat. West Sussex, United Kingdom: Blackwell Publishing; 2008:100-102.

    3. Harvey RG, Harari J, Delauche AJ. Ear Diseases of the Dog and Cat. Ames, Iowa: Iowa State University Press; 2001.

    4. Scott DW. Feline dermatology: 1900-1978. JAAHA 1980;16:331-459.

    5. Frost CR. Canine otoacariasis. J Small Anim Pract 1961;2:253-256.

    6. Park GS, Park JS, Cho BK, et al. Mite infestation rate of pet dogs with ear dermatoses. Korean J Parasitol 1996;34:143-150.

    7. Otranto D, Milillo P, Mesto P, et al. Otodectes cynotis (Acari: Psoroptidae): examination of survival off-the-host under natural and laboratory conditions. Exp Appl Acarol 2004;32(3):171-179.

    8. Scott DW, Horn RT. Zoonotic dermatoses of dogs and cats. Vet Clin North Am 1987;17:117-144.

    9. Herwick RP. Lesions caused by canine ear mites. Arch Dermatol 1978; 114:130-131.

    10. Hewitt M, Walton GS, Waterhouse M. Pet animal infestations and skin lesions. Br J Dermatol 1971;85:215-255.

    11. Lohse J, Rinder H, Gothe R, et al. Validity of species status of the parasitic mite Otodectes cynotis. Med Vet Entomol 2002;16(2):133-138.

    12. Pfister K. Tick and mite infestations. In: T. Schneider (ed). Veterinary Parasitology, ed 6 (special excerpt edition). Stuttgart, Germany: Parey; 2006:21-22.

    13. Sotiraki ST, Koutinas AF, Leontides LS, et al. Factors affecting the frequency of ear canal and face infestation by Otodectes cynotis in the cat. Vet Parasitol 2001;96:309-315.

    14. Moriello K. Clinical snapshot. Compend Contin Educ Pract Vet 2007;1:177-178.

    15. Larkin AD, Gaillard GE. Mites in cats' ears: a source of cross antigenicity with house dust mites. Ann Allergy 1981;46:301-304.

    16. Saridomichelakis MN, Koutinas AF, Gioulekas D. Sensitization to house dust mites in cats with Otodectes cynotis infestation. Vet Derm 1999;10(2):89-94.

    17. De Souza C. Validity and reproducibility of otoscopy and pinnal-pedal reflex on the diagnosis of Otodectes cynotis infestation in dogs. Rev Bras Parasitol Vet 2004;13:111-114.

    18. Ghubash R. Parasite miticidal therapy. Clin Tech Small Anim Pract 2006;21(3):135-144.

    19. Van de Heyning J, Theinpont D. Otitis externa in man caused by the mite Otodectes cynotis. Laryngoscope 1977;87(11):1938-1941.

    References »

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