2 May 2011
Hany Elsheikha, Paul Sands discuss the methodologies used to cure the case of a patient that presented with head shaking and ear rubbing of two weeks’ duration
THE ear mange mite Psoroptes cuniculi, a relatively common parasite in rabbits, causes damage to the rabbit’s external ear canal (Cutler, 1998).
The adult mite is a large, obligate, non-burrowing parasite that irritates the ear canal and may cause erythema and intense pruritus. Untreated infestations may cause serious economic losses due to weight loss, decreases in feed consumption, lower favourable feed conversion rates and the development of meningitis (Ulutas et al, 2005).
As many as 10,000 mites may inhabit a single pinna, creating a grey-brown mass of crusts and scabs that consists of live and dead mites, their wastes and inflammatory exudates (Harkness, 1987). The crusts and scabs can completely fill the external ear canal and the internal surface of the pinna.
Removing the crusts and treating topically may be painful, and cross-resistance to topically applied parasiticides is not uncommon (Pap et al, 1997).
Given the potential adverse effect of the parasitic infections on the health and welfare of rabbits, as well as the economic loss, a range of chemotherapeutic remedies has been used to treat P cuniculi infestation in rabbits. These include amitraz, pyrethroids and macrocyclic lactones. Psoroptes mites in rabbits are generally sensitive to the macrocyclic lactones, perhaps due to their longer persistent action compared to the other traditional preparations (benzyl benzoate, pyrethroids and organophosphates).
Auricular mange in rabbits can be difficult to treat. For example, a product like injectable ivermectin must be used as a dose of 0.4mg/kg SC, which is twice the recommended dose for ruminants (Jenkins, 2001). Additionally, multiple administrations or a larger dosage are typically needed.
Multiple treatments of ivermectin (Bowman et al, 1992; Kurade et al, 1996), doramectin (Narayanan et al, 2004; Kanbur et al, 2008), selamectin (Kurtdede et al, 2007; Farmaki et al, 2009) and moxidectin (Wagner and Wendlberger, 2000) have been reported to be effective against P cuniculi in rabbits. In addition, a spot-on formulation containing imidacloprid and moxidectin applied three times at four-week intervals resulted in complete elimination of psoroptic mites (Hansen et al, 2005). A single dose of 2mg/kg-1 of eprinomectin following topical administration (Wen et al, 2010), or a single dose of 200µg/kg or 300µg/kg bodyweight following SC administration (Pan et al, 2006) was sufficient to completely eliminate natural P cuniculi i nfestations in rabbits.
A two-year-old, female lopeared rabbit was presented with a history of head shaking and ear rubbing over two weeks.
Six weeks before referral to the authors, the rabbit was presented to the referring veterinarian with a fractured foreleg, which had been repaired by casting for four weeks.
The animal shared an outside hutch and enclosure with four other females. One male rabbit was kept in an adjacent enclosure.
On physical examination, the vertical ear canals were occluded with crusts and a dry brown exudate (Figure 1). Differential diagnoses included causes of otitis externa, such as auricular mange due to P cuniculi.
The severity of the lesion scored three (skin lesions involving one third to half of the auricle), based on the scoring given by Ulutas et al (2005). Attempts to remove a sample of the exudate caused great distress to the patient. No other abnormalities were detected. No ear or skin problems were noticed in the other rabbits. Clinical signs included three-quarters pruritus, pain, erythema and/or exudates (three-quarters), which were consistent with severe bilateral otitis externa.
To enable painless ear canal cleaning, the rabbit was sedated with fentanyl/fluanisone (0.5ml/ kg IM). The thickly layered crusted debris was removed as several large aggregates. Otoscopic examination revealed a smooth, moist, erythematous integument. Using a hand lens, parasites could be seen moving over the exudate.
Microscopical examination of the ear canal debris scrapings revealed the presence of large numbers of P cuniculi mites, including eggs and immature stages. Based on the collective diagnostic test results, the rabbit was diagnosed with otitis externa due to P cuniculi infestation.
The rabbit was treated with injectable ivermectin (400µg/ kg SC) on three occasions at 14-day intervals. Adjunct treatment included instillation of acaricidal ear drops containing diethanolamine fusidate, framycetin sulphate, nystatin and prednisolone into each ear daily for one week. Prior to the application of the ear drops, the ear canal and the surrounding area were gently cleaned and irrigated with saline to remove any excess exudate or debris that might prevent the product spreading over the entire external ear canal. Signs of aural discomfort ceased after one week of therapy.
Otoscopic examination after two and four weeks revealed normal ear canals without any inflammation or crusts.
A complete parasitological recovery was based on the disappearance of clinical signs of auricular mange, an absence of ear lesions and the absence of psoroptic mites.
Psoroptes species are common ectoparasites of rabbits, goats, horses and sheep.
P cuniculi in rabbits typically inhabits the external auricular meatus, where it is thought to feed mainly on serous exudate, skin secretions and blood, causing ceruminous otitis externa. However, other body areas may be affected.
P cuniculi is frequently demonstrated in apparently normal rabbits and stress may lead to an explosion in mite numbers, resulting in clinical disease (Bowman, 1992). Rabbits in poor condition appear to be most susceptible for the disease and several other factors – such as stress, overcrowding, poor nutrition, cold weather and/or immunosuppressants – predispose the animal to the disease. It is possible that earlier stresses of trauma, hospitalisation and fracture repair had contributed to the development of auricular mange in this particular rabbit.
Diagnosis of P cuniculi is generally based on an otoscopic examination of the external ear canal, a microscopical examination of scrapings for the presence of ear mites and clinical signs of pruritus, pain, erythema and/ or exudate. In the case presented here, otoscopic examination was a useful adjunct to evaluate the ear canal, and allowed us to obtain parasitological information.
Although microscopic examination is necessary to identify Psoroptes species, the large mites (up to 0.75• diameter) may be visible without magnification.
This mite is treated by cleaning the external ear canal, removing any debris or discharge, followed by instillation of an otic preparation with activity against this ear mite.
Systemic treatment has been reported to be effective, but no veterinary-licensed products exist in the UK for the treatment of P cuniculi infestation. Injectable ivermectin at a dose of 400µg/kg bodyweight weekly or biweekly has been recommended as the treat ment of choice. In the present case, adjunctive topical therapy was used to achieve rapid anti-inflammatory and acaricidal benefits, similar to the treatment of otodectic mange in dogs and cats (Mignon and Losson, 1996).
A formulation made up of diethanolamine fusidate, framycetin sulphate, nystatin and prednisolone is used for treating the micro-organisms commonly associated with otitis externa, including the ear mite, Otodectes cynotis, and is specifically formulated for treating otitis externa in the dog and cat.
Therapy and control of P cuniculi i nfestation are mainly based on the use of drugs and chemicals. However, the use of drugs to control these parasitic arthropods presents several challenges, including drug-resistance (Synge et al, 1995) and environmental damage (Halley et al, 1993).
Concern over toxicity (O’Brien, 1999) of many acaricides limits their use and reduces the number of safe, effective products available. These problems have led to research efforts to discover new alternatives for treating psoroptic mange in rabbits.
Some evidence exists that ear mite infestation in rabbits can be treated effectively with botanical products that do not contain chemical acaricides; for example, the acaricidal effects of the essential oil of Cinnamomum zeylanicum leaves (Fichi et al, 2007b) or of Eugenia caryophyllata cloves (Fichi et al, 2007a) were evaluated on P cuniculi, and were found to be safe and effective for the treatment of infested rabbits. In addition, a phyto-aromatic gel composed of volatile oils was found to have a strong and quick acaricidal activity against P cuniculi mites in experimentally infested rabbits (Mignon and Losson, 1996).
The identification of novel active, plant-derived natural compounds could increase the number of available chemotherapeutic agents, thereby reducing the frequency of resistance phenomena of arthropods and providing alternative drugs with greater acceptance, especially in terms of environmental safety.
Although it has been demonstrated that mites can survive up to 21 days off the host, it was decided not to attempt environmental control in this case, as the rabbits had a very large outdoor area available. It is important to treat not only the affected animal, but all those in contact because this mite is highly contagious. However, the owner declined to administer prophylactic acaricidal therapy to the in-contact rabbits.
Otitis externa due to P cuniculi infestation was diagnosed and evaluated in a rabbit with the aid of otoscopy.
Based on the results of this report, combined treatment with injectable ivermectin and acaricidal ear drops appear to be a viable treatment for otitis externa associated with P cuniculi infestation in rabbits.
A two-year-old, female lop-eared rabbit was presented for evaluation of head shaking and ear rubbing of two weeks’ duration. Physical examination revealed occlusion of the vertical ear canals with a dry, brown exudate. Based on clinical features, physical and otoscopic examination, a diagnosis of otitis externa due to Psoroptes cuniculi infestation was reached and a good prognosis was given. Combined treatment with injectable ivermectin and acaricidal ear drops proved curative.
Key words: rabbits, Psoroptes, ears.
Hany Elsheikha
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Paul Sands
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