Several types of mite are associated with ear problems, such as otitis externa, in animals (Scott et al, 2001). Approximately half of all otitis in cats, and 10% in dogs, are thought to be caused by ear mites (Sotiraki et al, 2001; (Mueller, 2008).
The most common mite is, undoubtedly, Otodectes cynotis, but other mites can also be found in the ear canal, including Demodex canis, Demodex cati, Sarcoptes scabiei and Notoedres cati (Cordero del Campillo et al, 1999; Blot et al, 2003; (Engler, 2007). Taxonomically all of these mites belong to the order Acarina and represent three different families, Psoroptidae, Demodecidae and Sarcoptidae (Table 1 ). Although there are some differences, their life cycle is very similar and entirely spent on the host. It lasts approximately 3 weeks and consists of four different stages: egg; larva; nymph; and adult (Quiróz-Romero, 1988; (Soulsby, 1988; Cordero del Campillo et al, 1999) (Figure 1).
| Phylum | Class | Order | Family | Genus | Species |
|---|---|---|---|---|---|
| Arthropoda | Arachnida | Acarina | Psoroptidae | Otodectes | Otodectes cynotis |
| Demodex canis | |||||
| Demodex injai | |||||
| Demodecidae | Demodex | Demodex cornei | |||
| Demodex cati | |||||
| Demodex gatoi | |||||
| Sarcoptidae | Sarcoptes | Sarcoptes scabiei | |||
| Notoedres | Notoedres cati |
Ear mites frequently result in otitis externa; their presence inside the ear canal triggers increased activity of the ceruminal glands, leading to a moist environment favourable to secondary infection by bacteria or fungi. These secondary infections and the animal's individual response may induce the progression of the initial disease (Angus, 2004; Engler, 2007; (Rosychuck, 2008). Moreover, some animals develop a hypersensitivity reaction to mites and their products. The number of mites necessary to promote disease can be very low (approximately two to three), triggering an Arthus-type and/or an immediate-type hypersensitivity reaction Scott et al, 2001; Sotiraki et al, 2001; (Angus, 2004). Young animals tend to be more susceptible to ear mites than adult ones, probably due to some immaturity in their immune system (Scott et al, 2001);(Lefkaditis et al, 2009).
This article looks at different types of mites responsible for ear problems in dogs and cats, focusing on their characteristics, diagnosis and management.
O. cynotis
O. cynotis is a non-burrowing mite with worldwide distribution and a broad host range, including cats, dogs, foxes, ferrets, racoons and, occasionally, humans (Six et al, 2000; Mullen and O'Connor, 2002; (Otranto et al, 2004). O. cynotis mites are large (650–800 μm), globosely shaped, white, very active and highly contagious parasites that live in the ear canal (Figure 2). They can also be found in the head, feet and tip of the tail (Simpson and Busby, 1999; Taylor et al, 2002; Fisher and Walsh, 2003; Curtis, 2004; Otranto et al, 2004; Farkas et al, 2007; (Mueller, 2008).
The entire life cycle of O. cynotis lasts about 3 weeks. The egg is laid by the female mite along with a secretion that keeps the egg stuck in place. After 4 days of incubation, the egg hatches to form a larva. The larva feeds for 3-10 days and turns into a protonymph, a deutonymph and, later, an adult (Figure 1) (Soulsby, 1988); (Bowman et al, 2002). Adult mites can live approximately 60 days and lay more than 90 eggs.
Adult mites generally feed on debris and tissue fluid from the outer layer of the skin but, occasionally, they pierce the skin to feed on blood, serum or lymph (Bowman et al, 2002); Mullen and O'Connor, 2002; (Otranto et al, 2004).
Demodex spp.
Demodex spp. are cigar-shaped mites (Figure 3) that can cause demodicosis, also known as red mange, in several animal species. Very common in dogs, demodicosis is rare in cats (Ortunez et al, 2009).
D. canis, in dogs, and D. cati, in cats, can be found in most healthy animals, as part of their normal cutaneous flora, in any hair follicle on the body including those present throughout the external ear canal, or within sebaceous glands Scott et al, 2001; (Angus, 2004). Demodicosis is more common in young animals and appears when the number of mites increase, for example when the animal is immunosuppressed.
Although D. canis (168 μm in length) is the most common mange mite in dogs, it is also possible to find Demodex injai and Demodex cornei. D. injai is approximately twice the size of D.canis and D. cornei is approximately half the size. Unlike D. canis and D. injai, D. cornei is located in the stratum corneum of the skin (Gortel, 2006).
Cats can be infested with D. cati and Demodex gatoi. D. cati is microscopically similar to D. canis and also lives in the hair follicles or sebaceous glands. D. gatoi, like D. cornei, resides in the stratum corneum of the skin, rather than within hair follicles. This demodectic mite has a stubby appearance and, unlike D. cati, is contagious (Saari et al, 2009).
S. scabiei and N. cati
S. scabiei and N. cati are burrowing mites that cause sarcoptic mange. Traditionally, S. scabiei is associ-ated with dogs and N. cati with cats, but the reverse can also occur. Adult mites cause mechanical irritation by excavating galleries into the skin. They are generally located in areas where hair is sparse, like the pinnae, elbows, hocks and ventral abdomen (Malik et al, 2006). It is rare to find evidence of these mites on routine ear cytology (Figure 4) (Angus, 2004).
Symptoms of ear mite infestation
Signs of ear mite infestation can be very variable, ranging from none to intense pruritus and skin lesions.
O. cynotis
When clinical signs are present, and as a result of intense pruritus, animals show excessive scratching of the ear, head shaking and dark brown crumbly wax, resembling coffee grounds (Figure 5). Usually, both ears are affected. They can be sensitive, painful and even swollen.
With advanced infestations, it is possible to have some bleeding of the ear canal, self-induced trauma, spasms and convulsions, especially in cats where it is associated with external otitis in the middle and inner ear. When the inner ear is affected, animals can also hold their head to one side and turn in circles (Quiróz-Romero, 1988; Simpson and Busby, 1999; Mullen and O'Connor, 2002). When the ear canal is massaged, the animal typically responds with pleasurable grunting sounds and by thumping its hind leg on the corresponding side (Mullen and O'Connor, 2002). Clinical signs associated with extra-ear locations are rare.
Demodex spp.
Clinical signs of canine demodicosis include erythema, alopecia, papules and pustules. If caused by D. canis, these signs are usually found on the head, with a periocular and perioral location, and also on the feet. D. injai is more frequently found on the dorsal trunk of adult dogs. Piodermas can occur, usually associated with secondary bacterial infection. A ceruminous ear infection, sometimes chronic, may also be present. Pruritis is not present in demodicosis unless secondary infections are present or when the etiological agent is D. cornei (Gortel, 2006; Tater and Patterson, 2008).
In cats, generalized infestations may be combined with mites inside the ear canal, along with a mild ceruminous otitis externa (Cordero del Campillo et al, 1999; Sotiraki et al, 2001; Akucewich et al, 2002; Blot et al, 2003; Rosychuck, 2008).
S. scabiei and N. cati
Sarcoptic mange is very pruritic. Dermatological signs of sarcoptic mange occur typically at elbows, hocks, face, ventral chest and pinnae, in the dog, and the face, ears and neck, in the cat, where it is also called face mange. Papules, scales and crusts are frequently seen at affected sites. Alopecia may also occur (Akucewich et al, 2002; Ghubash, 2006; Mueller, 2008). These mites more commonly affect the host's pinnae than the external ear canal. However, inflammation, glandular hyperplasia and increased cerumen production of the external canal can be present. Another important, although not pathognomonic, clinical sign that can be present, is the pinnal-pedal reflex (Gubash, 2006).
Ear mite transmission
O. cynotis
Transmission of O.cynotis can occur by direct contact between animals and also via fomites, i.e. via inanimate objects, like bedding material and grooming tools that are capabble of transmitting these mites (Simpson and Busby, 1999; Shanks et al, 2000). A common mode of transmission is from mother to offspring, eventually affecting the entire litter. Experimental studies, developed to determine off-host survival of O. cynotis mites, suggest that they could maintain infectivity for a period of 3–4 days (Otranto et al, 2004) and that they could survive for up to 8–12 weeks in the environment (Mueller, 2005; Mueller, 2007). These are very important findings with respect to control and prevention of auricular mites.
Animals that share cages for transport or grooming equipment are more susceptible to infestation, as such materials, as well as the environment, can be infested and require cleaning, disinfection and to be kept vacant for at least 12 days, to be sure that are free of ear mites (Otranto et al, 2004). In addition, fleas are thought to play an important role in ear mite transmission, carrying mites and eggs that adhere to them (Mueller, 2008).
Demodex spp.
Demodectic mites are generally non-contagious, since they belong to the normal cutaneous flora of animals. Demodicosis generally occurs when an animal's immune defences are fragile, allowing a mite overgrowth. Transmission frequently occurs between infested mothers and offspring during the first days of nursing, when the immune system of young animals is not yet fully established. Nevertheless, D. gatoi in cats and D. cornei in dogs can be transmitted by direct contact.
S. scabiei and N. cati
Sarcoptic mange is highly contagious between dogs and cats, and also has a great zoonotic potential (Cordero del Campillo et al, 1999; Taylor et al, 2002).
Sarcoptic mites can survive off the host for 24–36 hours at room conditions. In experimental conditions of 10 °C and 97% relative humidity, survival time was approximately 19 days (Arlian et al, 1984). These findings show that beyond direct contact, environmental contamination is also an important source of sarcoptic mange for animals and humans (Arlian et al, 1989).
Ear mite diagnosis
O. cynotis
Examination of the ear canal by otoscopy, or otic exudates by microscopy, will confirm the presence or absence of O. cynotis. However, diagnosis can be difficult if a low number of mites are present. O. cynotis usually leaves the ear canal and moves to other parts of the body and, as a consequence of the inflammatory process or secondary infections, mites can also be destroyed, reducing their number within the ear canal (Sotiraki et al, 2001).
Demodex spp.
The diagnosis of demodicosis is based on mites' identification in skin scrapings, hair plucks or ear swabs. Other techniques, like microscopic observation of exudate samples and acetate tape preparations, are also recommended (Gortel, 2006; Tater and Patterson, 2008).
S. scabiei and N. cati
Sarcoptic mange is diagnosed by direct microscopic identification of the mite, obtained by superficial skin scrapings. Dermatohistopathology and faecal flotation are techniques also available for sarcoptic mange diagnosis (Curtis, 2004). Table 2 describes several important and easily executable diagnostic techniques for identifying ear mites that do not require special skills or equipment. It is important to note that sample collection should always be performed before any treatment or therapy starts otherwise treatment may not be effective.
| Technique | Material | How to | To diagnose |
|---|---|---|---|
| Otoscopy | Magnified operating head otoscope | Direct visualization | Otodectes cynotis |
| Fibre optic video-assisted otoscopic endoscope | |||
| Microscopy | Cotton swab | With a cotton swab collect otic exudate from the ear canal | Otodectes cynotis |
| Mineral oil | Demodex spp. | ||
| Glass slide | Transfer exudate to the mineral oil, on the glass slide (KOH can also be used as a clearing agent) | Sarcoptes sabiei | |
| Notoedres cati | |||
| Observe under microscope (x4 or x10 objective) | |||
| Skin scraping | Microscope | Skin is squeezed during the scraping and a small amount of mineral oil is dropped on the skin or on the scraping instrument to trap the material for examination | Demodex spp. |
| Glass slide | Sarcoptes sabiei | ||
| Mineral oil | Notoedres cati | ||
| Scraping instrument (number 10 scalpel blades) | |||
| Scrape the skin until a capillary bleeding arises | |||
| Collect scraped material to a glass slide and proceed to microscopic observation | |||
| Place a coverslip over the scraped material | |||
| Observe under a microscope (lowering the condenser, increases contrast and facilitate observation) | |||
| Hair pluck | Forceps | Pluck hair from affected skin | Demodex spp. |
| Mineral oil | Place it under mineral oil and a coverslip | ||
| Glass slide | Observe in microscope (mites can often be seen within the follicular keratin) | ||
| Coverslip |
KOH, potassium hydroxide
Ear mite treatment
Treatment of ear mites will depend on the species present. Overall, it includes mechanical cleaning of the ear canal followed by topical or systemic drug administration, aiming to eradicate every mite.
Veterinary nurses should teach owners how to perform correct mechanical cleaning of the ear. The ear anatomy of dogs and cats is very different to that of humans, and owners must be aware of the differences and of the proper technique to execute effective cleaning (Nutall and Cole, 2004).
Ear cleaning is very important prior to treatment. It helps remove all debris, crusts and cerumen, allowing a better visualization of the tympanic membrane. Cleaning agents, such as warm water, saline solution or commercial ones like Otoclean® or Epioptic®, also facilitate the direct action of miticidal agents due to reduced organic matter within the ear canal (Scott et al, 2001; Blot et al, 2003; Curtis, 2004). The most effective miticidal agents usually contain ceruminolytic compounds, allowing a dual action: cleaning the ear canal and destroying mites. When aural preparations are used, the base of the ear should be gently massaged to disperse the oily preparation (Taylor et al, 2007).
Because some ear mites may survive outside the ear canal, they can be harboured on the body and re-infest ears, therefore topical and systemic treatment is highly recommended (Shanks et al, 2000; Six et al, 2000).
Several drugs have been used for ear mites:
In addition, cleaning of bedding, transport cages, grooming equipment and all other material that could have come into contact with mites is a very important measure to eliminate infestation and accomplish successful treatment.
Lans et al (2008) suggest a holistic approach to treating ear mites. Based on medicinal plants, they propose that the application of castor oil on a cotton ball in the external ear canal, once a day, for a week in combination with a mixture of several medicinal plants (Verbascum thapsus; Berberis aquifolium; Achillea millifolium; Glycyrrhiza glabra; Allium sativum) applied in the ear canal twice daily for 2–4 weeks, should be effective for O. cynotis treatment.
Ear mites: a persistent problem
When a dog or a cat is suspected of having ear mites, the first step is to confirm their presence by otos-copy, microscopy, skin scraping or hair pluck, and to identify the species present. All mites described have distinct morphological characteristics that must be present when trying to establish diagnosis. The tendency to immediately associate ear mites with O. cynotis is an erroneous practice and should be avoided. Another common error is to rely on the physical characteristics and odour of ear discharge. Although important, they cannot substitute a methodical examination and the realization of diagnostic techniques.
When the mite present is O. cynotis, D. cornei, S. scabiei or N. cati, it is necessary to treat all in-contact animals and replace or thoroughly disinfect bedding (Taylor et al, 2002; Ghubash, 2006). When Demodex spp. is found in the microscopic avaluation of otic exudates, a complete dermatological examination and skin scrapings should be realized.
For the treatment of ear mites, and specifically O. cynotis, there are some medications that must be applied in the ear canal once or twice daily, for approximately 3 weeks. Animals may strongly resent this procedure, since ear cleaning and the manipulation of the ear base can be very painful in affected animals, resulting in loss of compliance with the treatment regimen on the part of the owner (Six et al, 2000). Pet owners should be made aware of the importance of these actions, otherwise the treatment will be ineffective and the problems will persist.
It is important to remember, however, that there are many causes of ear disease beyond ear mites, such as foreign bodies, bacteria and fungi, which can promote similar clinical signs. Veterinary assistance is fundamental to establish a correct diagnosis and therapeutic plan.
Conclusion
Ear mites are common in pets and can cause a great deal of discomfort. Veterinary assistance is fundamental to establish a correct diagnosis and therapeutic plan. Veterinary nurses are well placed to provide advice on ear cleaning, and should advise pet owners to ensure that everything that has been in contact with a pet with mites has been thoroughly cleaned.