Psoroptes cuniculi (Ear Mange / Ear Canker)

Psoroptes cuniculi is a highly contagious, non-burrowing, obligate parasitic mite that primarily infests the external ear canal and surrounding skin of rabbits (Oryctolagus cuniculus). It is the most common cause of ear mange (ear canker) in domestic rabbits worldwide. The mite belongs to the family Psoroptidae, order Astigmata, and is characterized by its oval body, long pedicels with three-jointed pretarsi, and piercing mouthparts. Unlike Sarcoptes scabiei, P. cuniculi does not burrow into the skin but feeds on tissue fluids and lymph by piercing the epidermis, leading to intense pruritus, erythema, crusting, and secondary bacterial or fungal infections. The disease can also affect other lagomorphs and occasionally other species, but rabbits are the primary host. In severe cases, the infestation can extend to the head, neck, and body, causing systemic signs and significant welfare concerns. Early diagnosis and prompt treatment are essential to prevent chronic ear damage, secondary otitis media/interna, and neurological complications.

The sole causative agent is Psoroptes cuniculi, a non-burrowing mite of the family Psoroptidae. The mite is approximately 0.4-0.8 mm in length, with females slightly larger than males. It has a life cycle of about 21 days, consisting of egg, larva, protonymph, tritonymph, and adult stages. The entire life cycle occurs on the host, with eggs laid on the skin surface or in crusts. Transmission occurs primarily by direct contact with infested rabbits or contaminated fomites such as bedding, grooming tools, and cages. The mite can survive off the host for up to 21 days under favorable conditions (cool, humid environments), facilitating indirect transmission. The mite's mouthparts are adapted for piercing the stratum corneum and feeding on serous exudate and lymph, causing mechanical damage and an allergic inflammatory response. Secondary bacterial infections (e.g., Staphylococcus aureus, Pasteurella multocida) and fungal overgrowth (e.g., Malassezia) are common complications. Environmental factors such as overcrowding, poor hygiene, high humidity, and stress contribute to mite proliferation and disease severity.

Psoroptes cuniculi infestation is reported worldwide, with a higher prevalence in rabbitries, pet rabbit populations, and laboratory colonies. All breeds and ages of rabbits are susceptible, but young, geriatric, immunocompromised, or stressed individuals are more severely affected. The mite is highly contagious, and within a colony, up to 80-100% of rabbits may become infested if untreated. Direct contact is the primary mode of transmission, but indirect transmission via contaminated bedding, brushes, and handlers is also significant. The mite can survive off the host for up to 21 days, especially in cool, humid environments, facilitating spread. Wild rabbits (Sylvilagus spp.) may serve as reservoirs. In pet rabbits, the disease is often seen in multi-rabbit households or those with access to contaminated environments. Poor husbandry, inadequate ventilation, high stocking density, and lack of routine veterinary care increase the risk. The disease is more common in temperate climates with high humidity. There is no sex predilection, but intact males may have higher stress levels, increasing susceptibility. The zoonotic potential is negligible, but humans can develop transient dermatitis from mite exposure.

The pathophysiology of Psoroptes cuniculi infestation involves both mechanical damage and an allergic hypersensitivity reaction. The mites pierce the epidermis with their chelicerae, feeding on tissue fluids, lymph, and serous exudate. This mechanical injury disrupts the skin barrier, leading to erythema, edema, and pruritus. The mite's saliva and fecal material contain allergens that trigger a Type I (immediate) and Type IV (delayed) hypersensitivity response, characterized by mast cell degranulation, release of histamine and other inflammatory mediators, and infiltration of eosinophils, lymphocytes, and macrophages. This inflammatory cascade results in the formation of thick, brownish, crusty lesions (canker) in the ear canal and on the pinnae. The crusts are composed of dried serum, mite debris, and inflammatory cells. As the infestation progresses, the mites spread to adjacent skin, including the head, neck, and body, causing generalized dermatitis. Chronic infestation leads to hyperkeratosis, acanthosis, and fibrosis of the ear canal. Secondary bacterial infections (e.g., Staphylococcus aureus, Pasteurella multocida) and fungal overgrowth (e.g., Malassezia) exacerbate the inflammation and can lead to otitis externa, otitis media, and otitis interna. In severe cases, the infection can extend to the tympanic membrane, causing rupture and neurological signs such as head tilt, nystagmus, and ataxia. Systemic effects include anorexia, weight loss, and immunosuppression due to chronic stress and inflammation.

Intrinsic factors include species-specific anatomy: rabbits have a relatively narrow and convoluted ear canal, which predisposes to mite colonization and secondary infections. Age is a factor; young rabbits have a less developed immune system, while geriatric rabbits may have immunosenescence. Sex: intact males may have higher stress and aggression, increasing exposure. Breed: long-eared breeds (e.g., Lop rabbits) may have reduced ventilation of the ear canal, creating a favorable microclimate. Extrinsic factors include poor husbandry: overcrowding, inadequate sanitation, and high humidity facilitate mite survival and transmission. Stress from transport, weaning, or concurrent disease suppresses the immune response, increasing susceptibility. Nutritional deficiencies (e.g., vitamin A, zinc) can impair skin integrity and immune function. Lack of routine veterinary care and quarantine protocols for new rabbits allows introduction and spread of mites. Environmental factors such as temperature and humidity: mites thrive in cool, humid conditions (20-30°C, >50% humidity). Inappropriate use of topical insecticides (e.g., fipronil) can cause toxicity and worsen clinical signs. Concurrent diseases (e.g., pasteurellosis, dental disease) may predispose to infestation.

Clinical signs typically begin with intense pruritus of the ears, leading to head shaking, scratching, and rubbing of the ears against objects. The ear canal and pinnae become erythematous and edematous, with the formation of thick, brownish, crusty exudate (canker) that may fill the ear canal and extend to the surrounding skin. The crusts are often dry and adherent, and removal may reveal a raw, bleeding, and ulcerated surface. As the infestation progresses, the mites spread to the head, neck, and body, causing generalized dermatitis with alopecia, scaling, and crusting. Secondary bacterial infections can produce purulent discharge and a foul odor. In chronic or severe cases, otitis media/interna may develop, leading to neurological signs such as head tilt, nystagmus, ataxia, and circling. Systemic signs include anorexia, weight loss, depression, and pyrexia. In advanced cases, rabbits may become moribund due to pain, secondary infections, and sepsis. The disease is often bilateral, but one ear may be more severely affected. In some rabbits, the infestation may be subclinical, with mites present but minimal clinical signs, especially in early stages or in immunocompetent individuals.

Differential diagnoses for Psoroptes cuniculi infestation include: 1) Sarcoptes scabiei (sarcoptic mange): burrowing mite that causes intense pruritus, alopecia, and crusting, but typically affects the face, ears, and extremities; skin scrapings reveal burrowing mites. 2) Cheyletiella parasitovorax (walking dandruff): causes scaling and pruritus, but mites are larger and visible on the skin surface; skin scrapings or acetate tape preparations reveal mites. 3) Notoedres cati (notoedric mange): rare in rabbits, but can cause similar ear lesions; skin scrapings reveal mites. 4) Otodectes cynotis (ear mite): more common in cats and dogs, but can infest rabbits; causes otitis externa with dark, crumbly discharge; mites are visible on otoscopic examination. 5) Bacterial otitis externa (e.g., Staphylococcus aureus, Pasteurella multocida): causes purulent discharge, erythema, and pain; cytology and culture identify bacteria. 6) Fungal otitis externa (e.g., Malassezia, Aspergillus): causes waxy, yellowish discharge; cytology and culture identify yeast/fungi. 7) Allergic dermatitis (e.g., atopy, food allergy): causes pruritus, erythema, and self-trauma, but no mites on skin scraping; response to allergen avoidance or antihistamines. 8) Dermatophytosis (ringworm): causes circular areas of alopecia and scaling, but pruritus is variable; fungal culture or PCR confirms. 9) Trauma or foreign body in the ear canal: causes head shaking and scratching; otoscopic examination reveals foreign material. 10) Neoplasia (e.g., squamous cell carcinoma): causes mass lesions in the ear; biopsy confirms. Definitive diagnosis is based on identification of Psoroptes cuniculi mites, eggs, or feces in skin scrapings, ear swabs, or crusts.

The diagnostic approach for suspected Psoroptes cuniculi infestation follows a systematic algorithm: 1) Clinical triage: Obtain a thorough history, including onset, progression, contact with other rabbits, and husbandry practices. 2) Physical examination: Perform a complete physical exam, with special attention to the ears, head, and skin. Observe for head shaking, scratching, and crusty lesions. 3) Species-safe restraint: For rabbits, use a towel wrap or have an assistant gently restrain the rabbit to avoid injury. 4) Otoscopic examination: Examine the ear canals with an otoscope to visualize mites, crusts, and discharge. Mites may be seen as small, white, moving dots. 5) Skin scraping: Collect deep skin scrapings from the edge of crusts or affected skin using a scalpel blade. Place the material on a slide with mineral oil and examine under low-power microscopy for mites, eggs, and fecal pellets. 6) Ear swab: Collect a swab from the ear canal and roll onto a slide for cytology (Diff-Quik or Gram stain) to identify mites, bacteria, and yeast. 7) Acetate tape preparation: Press a clear acetate tape onto the skin surface and examine under the microscope for mites or eggs. 8) Fecal flotation: Not typically necessary, but mites may be found in feces if ingested during grooming. 9) Blood work: If systemic signs are present, perform a CBC and serum biochemistry to assess for secondary infections, dehydration, and organ dysfunction. 10) Imaging: If otitis media/interna is suspected, perform radiography (skull views) or CT to evaluate the tympanic bullae. 11) Response to treatment: A therapeutic trial with an acaricide (e.g., ivermectin) can be both diagnostic and therapeutic. If clinical signs resolve, the diagnosis is confirmed. 12) Rule out differentials: If mites are not found, consider other causes of ear disease and perform appropriate tests (e.g., bacterial culture, fungal culture, allergy testing).

In uncomplicated Psoroptes cuniculi infestation, laboratory findings are often unremarkable. However, in chronic or severe cases, a complete blood count (CBC) may reveal eosinophilia, which is common in parasitic infestations, and leukocytosis with a left shift if secondary bacterial infection is present. Serum biochemistry may show elevated globulins due to chronic inflammation, and decreased albumin due to protein loss through exudative skin lesions. Dehydration may be reflected in elevated total protein, packed cell volume (PCV), and blood urea nitrogen (BUN). If the rabbit is anorexic, there may be hypoglycemia, electrolyte imbalances (e.g., hypokalemia), and elevated liver enzymes (AST, ALT) due to hepatic lipidosis. Fecal analysis is not typically diagnostic, but mites may be found in feces if the rabbit ingests them during grooming. PCR testing for Psoroptes cuniculi is available but not routinely used; it can be performed on skin scrapings or ear swabs for definitive species identification. Serology is not commonly used. Urinalysis may show ketonuria if the rabbit is in negative energy balance. In cases with secondary otitis media/interna, cerebrospinal fluid analysis may show increased protein and nucleated cell count, but this is rarely performed. Overall, laboratory findings are supportive but not diagnostic; the definitive diagnosis is based on mite identification.

Imaging is not routinely required for the diagnosis of Psoroptes cuniculi infestation, but it is valuable in cases with suspected otitis media/interna or when the infestation is severe and chronic. Radiography of the skull (lateral, dorsoventral, and oblique views) can reveal thickening of the tympanic bulla, increased opacity within the bulla, or lysis of the surrounding bone, indicating otitis media. However, radiography has low sensitivity for early changes. Computed tomography (CT) is the imaging modality of choice for evaluating the ear canals and tympanic bullae in rabbits. CT can detect soft tissue changes, fluid accumulation, and bone remodeling with high detail. Magnetic resonance imaging (MRI) provides superior soft tissue contrast and is useful for assessing the brain and inner ear in cases of otitis interna. Ultrasonography of the ear canal may be performed but is limited by the small size and bony structures. In cases of generalized dermatitis, imaging is not necessary. For rabbits with neurological signs, advanced imaging (CT or MRI) is recommended to rule out other causes such as encephalitozoonosis, vestibular disease, or neoplasia. Imaging findings in Psoroptes cuniculi infestation include thickening of the ear canal wall, presence of soft tissue density material in the canal, and, in chronic cases, mineralization of the tympanic membrane or bulla. These findings, combined with clinical signs and mite identification, support the diagnosis.

Cytological examination of ear swabs, skin scrapings, or crusts is essential for diagnosis. Direct smears stained with Diff-Quik or Gram stain may reveal mites, eggs, fecal pellets, inflammatory cells (eosinophils, neutrophils, macrophages), bacteria, and yeast. Mites are large (0.4-0.8 mm) and have a characteristic oval body with long legs; eggs are oval and translucent. Fecal pellets are small, brown, and granular. Cytology can also identify secondary bacterial (cocci or rods) and fungal (yeast) infections. Histopathology of skin biopsies is not typically performed for diagnosis but may be useful in chronic cases or when the diagnosis is uncertain. Histological findings include hyperkeratosis, acanthosis, spongiosis, and infiltration of the dermis with eosinophils, lymphocytes, and mast cells. The stratum corneum may contain mites, eggs, and fecal material. In chronic cases, there is fibrosis and sebaceous gland hyperplasia. If a biopsy is taken from the ear canal, it may show ulceration and granulation tissue. Histopathology can also rule out neoplasia or other dermatopathies. In cases with otitis media, histopathology of the tympanic bulla may reveal inflammatory exudate and fibrosis. Overall, cytology is the most practical and cost-effective diagnostic tool, while histopathology is reserved for atypical cases.

Treatment of Psoroptes cuniculi infestation involves a multimodal approach: 1) Isolation: Infested rabbits should be isolated from other rabbits to prevent spread. 2) Environmental decontamination: Thoroughly clean and disinfect the rabbit's environment, including cages, bedding, and grooming tools. Discard bedding and treat the environment with an acaricide (e.g., permethrin spray) after removing the rabbit. 3) Manual removal of crusts: Gently soften and remove crusts from the ear canal and surrounding skin using a warm saline solution or a ceruminolytic agent. This should be done carefully to avoid pain and bleeding. 4) Topical therapy: Apply a topical acaricide (e.g., ivermectin or selamectin) directly to the affected areas. However, topical application may be less effective than systemic therapy. 5) Systemic therapy: The drug of choice is ivermectin (0.2-0.4 mg/kg SC or PO, repeated every 10-14 days for 2-3 treatments) or selamectin (6-18 mg/kg topically, repeated every 30 days). Moxidectin (0.2-0.5 mg/kg PO or SC) is also effective. 6) Analgesia: Provide pain relief with non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam (0.3-0.6 mg/kg PO or SC q24h) or opioids (e.g., buprenorphine 0.01-0.05 mg/kg SC or IV q8-12h) if severe pain. 7) Antibiotics: If secondary bacterial infection is present, administer appropriate antibiotics based on culture and sensitivity. Common choices include enrofloxacin (5-15 mg/kg PO or SC q12-24h) or trimethoprim-sulfamethoxazole (30 mg/kg PO q12h). 8) Antifungals: If fungal overgrowth is present, use topical or systemic antifungals such as clotrimazole or itraconazole (5-10 mg/kg PO q24h). 9) Supportive care: Ensure adequate hydration and nutrition. If the rabbit is anorexic, provide syringe feeding with a critical care formula (e.g., Oxbow Critical Care) and fluid therapy (e.g., lactated Ringer's solution 50-100 ml/kg SC or IV q24h). 10) Husbandry corrections: Improve hygiene, reduce stress, and ensure proper nutrition. 11) Follow-up: Re-examine the rabbit after 2-3 weeks to assess response and repeat treatment if necessary. 12) Treat all in-contact rabbits, even if asymptomatic, to prevent reinfestation.

The prognosis for uncomplicated Psoroptes cuniculi infestation is excellent with prompt and appropriate treatment. Most rabbits respond well to systemic acaricides, and clinical signs resolve within 2-4 weeks. However, the prognosis is guarded in cases with secondary bacterial or fungal infections, chronic otitis media/interna, or systemic involvement. If the infestation is left untreated, it can lead to severe ear damage, hearing loss, neurological deficits, and even death due to secondary sepsis or starvation. Negative prognostic indicators include: duration of infestation > 6 weeks, presence of neurological signs (head tilt, ataxia), severe secondary infections, concurrent diseases (e.g., pasteurellosis, immunosuppression), and poor husbandry conditions. With appropriate treatment, the recovery rate is high, but recurrence is possible if environmental decontamination is incomplete or if in-contact animals are not treated. Long-term management may be required for chronic cases, including regular ear cleaning and monitoring. Overall, the prognosis is good to excellent for most rabbits, but early intervention is key.

Follow-up care is essential to ensure complete resolution and prevent recurrence. Schedule a re-examination 2-3 weeks after initiation of treatment to assess clinical response. At this visit, perform a physical exam, otoscopic examination, and skin scrapings to confirm the absence of mites. If mites are still present, repeat the acaricide treatment. For rabbits with secondary infections, re-check cytology and adjust antibiotics/antifungals as needed. For rabbits with otitis media/interna, repeat imaging (CT or radiography) after 4-6 weeks to evaluate the tympanic bullae. Monitor weight and body condition weekly during treatment. Provide the owner with detailed instructions on environmental decontamination, including washing bedding in hot water, vacuuming, and applying acaricide sprays. Advise quarantine of new rabbits for at least 2 weeks before introduction. Long-term follow-up every 3-6 months is recommended for chronic cases to monitor for recurrence. Educate the owner on proper husbandry, including regular ear cleaning, stress reduction, and balanced nutrition. If neurological signs persist, consider referral to a veterinary neurologist. Document all treatments and responses in the medical record.

Pearls: 1) Always perform a thorough otoscopic examination in rabbits with head shaking or ear scratching; Psoroptes cuniculi is the most common cause. 2) Use a warm saline solution to soften crusts before removal to minimize pain and bleeding. 3) Systemic ivermectin is highly effective and easier to administer than topical treatments. 4) Treat all in-contact rabbits, even if asymptomatic, to prevent reinfestation. 5) Provide analgesia (e.g., meloxicam) to reduce pain and inflammation. 6) Educate owners on the importance of environmental decontamination to prevent recurrence. 7) In chronic cases, consider secondary bacterial/fungal infections and treat accordingly. 8) Use a sterile mineral oil preparation for skin scrapings to improve mite visualization. 9) In severe cases, consider sedation or anesthesia for ear cleaning to avoid stress and injury. 10) Always rule out other causes of ear disease (e.g., bacterial otitis, foreign bodies) if mites are not found. Pitfalls: 1) Do not use fipronil (Frontline) in rabbits; it is highly toxic and can cause severe neurological signs and death. 2) Avoid using topical corticosteroids without concurrent acaricidal therapy, as they can suppress the immune response and worsen the infestation. 3) Do not use ivermectin at doses >0.4 mg/kg in rabbits, as it can cause neurological toxicity. 4) Do not neglect environmental decontamination; otherwise, reinfestation is likely. 5) Do not assume that the absence of mites on a single skin scraping rules out infestation; multiple scrapings may be needed. 6) Do not use over-the-counter flea treatments for dogs or cats on rabbits, as they may contain toxic ingredients. 7) Do not ignore secondary infections; they can lead to systemic illness. 8) Do not delay treatment in severe cases, as neurological complications can become irreversible. 9) Do not forget to treat the rabbit's environment and in-contact animals. 10) Do not use ear drops containing alcohol or other irritants, as they can cause pain and further inflammation.

Based on Carpenter's Exotic Animal Formulary (6th edition) and current literature, the following drug protocols are recommended for Psoroptes cuniculi infestation in rabbits: 1) Ivermectin: 0.2-0.4 mg/kg SC or PO, repeated every 10-14 days for 2-3 treatments. This is the most commonly used and highly effective treatment. 2) Selamectin (Revolution): 6-18 mg/kg topically, applied to the back of the neck, repeated every 30 days for 2-3 treatments. It is safe and effective, with a broader spectrum against other parasites. 3) Moxidectin: 0.2-0.5 mg/kg PO or SC, repeated every 14 days for 2-3 treatments. It is also effective but may have a narrower safety margin. 4) Doramectin: 0.2-0.3 mg/kg SC, repeated every 10-14 days. 5) Eprinomectin: 0.5 mg/kg topically, applied once, but safety data in rabbits is limited. 6) For secondary bacterial infections: Enrofloxacin (Baytril) 5-15 mg/kg PO or SC q12-24h; Trimethoprim-sulfamethoxazole 30 mg/kg PO q12h; or Chloramphenicol 50 mg/kg PO q8h (but use with caution due to human health risks). 7) For pain and inflammation: Meloxicam 0.3-0.6 mg/kg PO or SC q24h; Carprofen 2-4 mg/kg PO or SC q12-24h; or Buprenorphine 0.01-0.05 mg/kg SC or IV q8-12h. 8) For fungal overgrowth: Itraconazole 5-10 mg/kg PO q24h; or topical clotrimazole 1% solution applied to affected areas q12h. 9) Fluid therapy: Lactated Ringer's solution or Normosol-R at 50-100 ml/kg SC or IV q24h, adjusted based on hydration status. 10) Nutritional support: Oxbow Critical Care or similar formula, 10-20 ml/kg PO q6-8h, if anorexic. 11) Environmental decontamination: Permethrin spray (0.05-0.1%) applied to the environment after removing the rabbit; ensure it is dry before reintroducing the rabbit. 12) Ear cleaning: Use a ceruminolytic agent (e.g., Epi-Otic) diluted 1:1 with warm water, instilled into the ear canal, followed by gentle massage and wiping. Always consult the latest formulary for updated dosages and safety information.

Evidence-based literature on Psoroptes cuniculi infestation in rabbits is extensive. Key studies include: 1) A study by Curtis et al. (1990) demonstrated the efficacy of ivermectin at 0.4 mg/kg SC given twice, 14 days apart, achieving a 100% cure rate in naturally infested rabbits. 2) A comparative study by McKellar et al. (1992) showed that selamectin at 6 mg/kg topically was as effective as ivermectin, with no adverse effects. 3) A study by Vercruysse et al. (1993) evaluated moxidectin at 0.2 mg/kg SC and found it effective, but with a slightly lower cure rate than ivermectin. 4) A review by Meredith (2015) in the BSAVA Manual of Rabbit Medicine highlighted the importance of environmental decontamination and treating all in-contact animals. 5) A study by Fisher et al. (2001) reported that fipronil is toxic to rabbits, causing neurological signs and death, and should be avoided. 6) A consensus statement by the Association of Exotic Mammal Veterinarians (AEMV) recommends ivermectin or selamectin as first-line treatments, with a follow-up examination at 2-3 weeks. 7) A study by Harkness and Wagner (1995) described the life cycle and pathogenesis of Psoroptes cuniculi, emphasizing the allergic component. 8) A recent study by Di Girolamo et al. (2019) evaluated the use of oral fluralaner (Bravecto) at 25 mg/kg, which showed promising results with a single dose, but further research is needed. 9) A study by Mancinelli et al. (2016) reported on the use of CT to diagnose otitis media in rabbits with chronic ear disease, highlighting the value of advanced imaging. 10) A review by Varga (2014) in the Textbook of Rabbit Medicine discussed the clinical signs and treatment protocols, emphasizing the need for analgesia and supportive care. Overall, the evidence supports the use of systemic macrocyclic lactones (ivermectin, selamectin, moxidectin) as the cornerstone of therapy, with a high success rate and minimal adverse effects when used at appropriate dosages. Environmental control and treatment of all in-contact animals are essential to prevent reinfestation.