Cathy’s Critter Corner: Small mammal dermatology, Part 2 — Rabbits
Associate IndeVet Dr. Cathy Emery has a wealth of knowledge about exotics. Cathy’s Critter Corner is a column where she takes an in-depth look at common exotics issues. Last time, her focus was on ferrets. This time, she explores rabbit dermatology.
The scabbed, the bald, and the itchy: Rabbit dermatology
Dermatological complaints are common reasons for small mammals to present for veterinary care. We previously discussed the presenting signs, historical clues, and diagnostic tests that are important in the workup of skin disease in small mammals, along with dermatological diseases of ferrets. Now we’ll use that information and apply it to skin and coat conditions in rabbits, another common small mammal companion pet.
Unique Rabbit Features
Rabbits, like ferrets, have hair present on their pinnae and four sets of mammary glands. Their only apocrine sweat glands are located on their lips and provide a very inefficient means of cooling. All rabbits lack footpads, relying on fur to protect their feet. The Rex breed has no secondary haircoat (guard hairs), which contributes to its especially soft texture and makes it even more susceptible to pododermatitis.
Rabbits shed twice yearly; molting typically starts cranially and progresses caudally, sometimes with a very discrete line of demarcation along the shed zone. An important fact to keep in mind when treating rabbits for ectoparasites is that they are uniquely sensitive to fipronil and should not be treated with it in any form, as it can be fatal.
Husbandry plays a large role in many rabbit skin conditions. External trauma has the potential to cause abscess formation; rabbit abscesses are notoriously difficult to drain due to the thick consistency of their pus and are often managed more effectively by excision or marsupialization (in conjunction with antibiotics).
Use caution when applying any topical antibiotics, as rabbits are likely to ingest them and could suffer dysbiosis as a result (in particular avoid polymyxin, neomycin, mupirocin; silver sulfadiazine is the topical of choice).
An important rule out for subcutaneous nodules resembling abscesses in outdoor rabbits is the Cuterebra warble, typically encountered in the summer and fall when botfly larvae are emerging. The swellings will have a central pore with a creamy-gray second or third instar larva visible within.
Similar to treatment in other species, the breathing pore should be enlarged and the larva gently extracted, taking care not to rupture it due to risk of infection, inflammation, and anaphylaxis. The site is then flushed, debrided if necessary, and left to heal by second intention with topical silvadene applied as needed. Consideration should be given to imaging affected individuals with radiographs or ultrasound, as Cuterebra larvae can migrate internally.
Outdoor rabbits are at risk for fly strike in the summer, particularly those kept in dirty enclosures and suffering from other ailments (reduced mobility, urine scald, etc). Treatment is similar to myiasis in other species: clip and clean the affected area(s), apply Capstar to the maggots and give systemic ivermectin, supportive care with fluids, systemic antibiotics (TMS, fluoroquinolones), and pain medication (meloxicam +/- gabapentin, opioid). Euthanasia may be warranted in severe cases, especially those with underlying conditions.
Urine scald may be seen in individuals that are overweight, have reduced mobility, and/or are suffering from urinary tract disease (cystitis, uroliths, sludge). In addition to working up (radiographs, urinalysis) and treating (pain medication, antibiotics, diet change, surgery) the underlying cause, the affected area should be gently clipped, cleaned, and dried. Silver sulfadiazine can be applied to ulcerated areas; once open lesions have healed, corn starch may be applied judiciously to help keep the skin dry, and bedding should be cleaned frequently.
Similar to urine scald, chin scald—aka Slobbers—can be seen with dental disease or on its own when the dewlap area remains persistently moist. Dermatitis may progress to severe cellulitis of the ventral neck with swelling, ulceration, pain, and fever developing. Staphylococcus aureus and Pasteurella multocida are common colonizers in this area, but Pseudomonas occasionally occurs and can turn the fur blue.
Aggressive cleaning and debridement should be performed and the affected individual placed on systemic antibiotics, ideally based on culture and sensitivity, and pain medication. Topical silver sulfadiazine is a useful adjunctive therapy or may be used as sole therapy in mild cases. Underlying factors that contribute to dermatitis development must be addressed for successful resolution and prevention: weight loss in obese individuals, dental remediation in those with dental disease, and improved husbandry to maintain a clean, dry environment.
As alluded to earlier, pododermatitis can be a frustrating problem in rabbits due to their lack of footpads. Overweight and sedentary animals, Rex rabbits, and those housed on hard or wire surfaces are most susceptible.
Lesions are typically seen on the ventral hocks and start as a circular area of hair loss and reddened skin. If left untreated, they can progress from superficial to deep ulcerations with secondary infection and even lead to osteomyelitis of the underlying tarsal +/- metatarsal bones. Occasionally, similar lesions may be seen on the metacarpal/phalangeal region of the front limbs.
Once lesions have progressed beyond superficial ulceration, they are very difficult to treat, and bony involvement warrants a guarded prognosis. Culture of deep lesions and bone is strongly recommended to guide long-term antibiotic therapy. Affected areas (including bone) should be debrided, with silver sulfadiazine or another suitable topical applied (hydrogel, Manuka honey); therapeutic laser has shown promise in helping to manage this condition.
Any means of reducing pressure on the affected area(s) should be attempted, although rabbits in general do not tolerate bandages very well. Special attention should be paid to managing pain and inflammation, and any concurrent contributing factors must be addressed (weight loss, environmental cleanliness, bedding substrate).
All areas where the rabbit resides should be thoroughly padded, ideally with foam mats covered with baby fleece material. Frequent rechecks with repeat debridement are often necessary; a successful outcome requires a dedicated owner, as resolution may take several months.
Ectoparasites: Fleas, Ticks, and Lice
Pet rabbits can acquire fleas from other household pets (Ctenocephalides felis) or wild rabbits (Spilopsyllus cuniculi, which is host-specific). Symptoms range from minimal to severe pruritus with secondary infection, anemia, and death.
Diagnosis is straightforward via identification of fleas or flea dirt; topical Revolution or Advantage/Advantage Multi is the treatment of choice (not fipronil!), although recently oral fluralaner (Bravecto) at 20-25 mg/kg has been shown to be safe and effective for treating fleas in rabbits. Again, all household animals should be treated.
In cases where the rabbit flea is involved the risk of myxomatosis exists. New World wild rabbits act as the relatively resistant reservoir for this viral disease, which is transmitted by insect vectors (fleas, mosquitoes, flies, possibly ticks) and direct contact to extremely susceptible Old World/European pet rabbits.
Incubation ranges from 8-21 days; clinical signs include edema of the head, ears, eyelids, and genitalia with oculonasal discharge; firm erythematous skin nodules; lethargy; fever; and anorexia. Disease may be diagnosed through viral isolation and histopathology. There is no successful treatment; infection is usually fatal, making vector control and parasite prevention vital for preventing this devastating disease, which, in the U.S., is more prevalent on the West Coast.
Other arthropod (fleas, mosquitoes, ticks) vectored viral diseases include Rabbit (Shope) fibroma virus and papillomavirus. Both are endemic in the Eastern cottontail population and are occasionally transmitted to domestic rabbits.
The fibroma virus, a poxvirus, causes the development of large, flat subcutaneous nodules of the feet, limbs, face, and perineum. Affected areas may necrose and slough or lesions may regress over several months; supportive care and antibiotics as needed for secondary infections should be provided in the interim.
The papillomavirus leads to the development of raised, wart-like, sometimes pigmented lesions on the eyelids, ears, trunk, and thighs of affected individuals. These lesions may undergo spontaneous remission over the course of several months or they could undergo malignant transformation to squamous cell carcinoma.
Histopathology and viral isolation can be used to diagnose both viral diseases, although in domestic rabbits papillomavirus particles are rarely found in tissue samples. Isolated lesions may be cured by excision and vector control.
Less common ectoparasites include ticks and lice. Multiple tick species can parasitize outdoor rabbits; thankfully, tickborne diseases—other than the viral ones mentioned above—seem uncommon in this species. Identification and removal are straightforward; ticks may be prevented with the routine application of Revolution/Advantage Multi or fluralaner given orally.
The rabbit louse, Haemodipsus ventricosus, is more common in dwarf species of rabbit, although it is still a rare occurrence. Affected individuals are typically quite pruritic. Diagnosis is by visual inspection and/or skin scrapings/hair plucks. Advantage multi or Revolution may be applied every 21-28 days as treatment/prevention.
Multiple types of mites can affect rabbits, each with varying degrees of pruritus. The saliva of the rabbit ear mite, Psoroptes cuniculi, causes intense inflammation and subsequent otitis externa; severe cases can progress to otitis media with neurologic signs (torticollis, nystagmus, head tilt). Spread is via direct transmission.
Most commonly a droopy ear, head shaking, and ear scratching are seen. Thick yellow-brown adherent crusts are visible in the ear canals; occasionally infestation can spread to other areas of the body, resulting in focal areas of alopecia. An ear smear under mineral oil evaluated microscopically should provide a ready diagnosis.
As tempting as it may be to thoroughly clean the ears of affected individuals, this is not recommended due to the extreme pain and discomfort it causes. Instead, systemic anti-parasiticides like ivermectin (SQ or PO every 2 weeks for 2-3 treatments), Revolution (every 2 weeks for 2-3 treatments), Advantage multi (every 30 days for 3 treatments) or oral fluralaner (one dose) should be administered to affected and in-contact rabbits. It’s a good idea to recheck these rabbits around 30 days into treatment, as occasionally secondary bacterial otitis may occur and necessitate follow up treatment with a topical antibacterial agent like Baytril Otic.
Cheyletiella parasitovorax, the rabbit fur mite, is a non-burrowing mite that causes “walking dandruff,” named such due to the scaly dermatosis it causes. Flakiness and pruritus can range from mild to severe, with the flaky buildup +/- alopecia most typically seen on the dorsal shoulders and topline. Tape preps or skin scrapings may be used to diagnose the mite by direct visualization and/or the presence of eggs adhered to hair shafts.
This is a zoonotic organism and can affect multiple mammalian species, thus consideration should be given to treating all household pets. Ivermectin (every 2 weeks), Revolution (monthly), Advantage multi (monthly), and fluralaner (once) are all effective. Lime sulfur dips, while effective, are stressful and messy; given the prevalence of easier, safer therapies it is no longer a favored treatment.
Other less common mites that may affect rabbits include Notoedres cati and Leporacarus gibbus. Notoedres may cause cutaneous areas of hair loss, erythema, and crusting, while Leporacarus can lead to scaly areas of alopecia with self-mutilation due to a hypersensitivity reaction. Sarcoptes scabiei and Demodex cuniculi are seen even less frequently. Treatment is similar to that for Cheyletiella, above.
Ringworm in rabbits is most commonly caused by Trichophyton mentagrophytes, although cases of Microsporum canis are seen from time to time. Many affected rabbits are asymptomatic carriers, but young or immunosuppressed individuals may show signs of disease including hair loss with dry, crusty, inflamed skin, typically of the face, legs, feet, and nail beds. Pruritus is variable. Fungal culture/DTM or occasionally a trichogram may be used to obtain a diagnosis with follow-up cultures/DTMs performed to assess treatment efficacy.
Recommended therapies include oral azoles or griseofulvin (not in pregnant animals) for a month or more, terbinafine for up to 6 weeks, or, less ideally, the application of lime sulfur dips at a 1:32 dilution 1-2 times a week for a month. Clipping is not recommended due to the stress it causes. All in-contact individuals should be treated due to the possibility of asymptomatic carriers, and the environment should be repeatedly disinfected.
Another contagious organism responsible for dermatological lesions in rabbits is Treponema paraluiscuniculi, the causative agent of rabbit syphilis, or venereal spirochetosis. This is a species-specific organism and does not have zoonotic potential. The spirochete is transmitted through venereal or direct contact; most pet rabbits are infected at birth or while nursing. Wild rabbits can also be a source of infection.
The incubation period ranges from 3-16 weeks with some individuals remaining asymptomatic for years. Lesions include crusting and erythema of the face (nose, lips, eyelids) and perineum; more severe cases may develop edema, vesicles, ulcers, and/or proliferative lesions in those areas. Lesions are more painful than pruritic. Pregnant does may abort or have litters that die shortly after birth.
Diagnosis requires biopsy of affected tissue with silver staining or serology; more commonly, diagnosis is made via the exclusion of other causes, distinctive lesions, and response to treatment. Penicillin G given at 40,000-80,000 IU/kg SQ weekly for three treatments is the treatment of choice (do not give Penicillin orally; while dysbiosis is not as common with the subcutaneous route, it is still possible—treated rabbits should be monitored closely and consideration given to providing a probiotic for the duration of therapy). Chloramphenicol at 55mg/kg q12h for 4 weeks has also been used with some success. All in-contact individuals should be treated.
Self-mutilation and barbering can occur in rabbits, but they are not common causes of hair loss. Occasionally a dominant rabbit will barber a cagemate, creating patchy areas of broken hairs on the neck and back. Sometimes does going through estrus or individuals on a low-fiber diet will self-barber.
Self-mutilation has also been reported after IM injection of ketamine and xylazine; therapy with meloxicam and gabapentin may help alleviate symptoms and the drugs should be administered in separate locations, if at all, in the future. Other causes of pruritus and/or pain should be ruled out before a diagnosis of barbering is made.
Sudden development of non-pruritic regional complete alopecia, especially in the lumbosacral area or flanks should raise suspicion for telogen defluxion, which may occur 2-3 months after a stressful event (illness, surgery, pregnancy/lactation). Hair should regrow normally with time.
Sebaceous adenitis is an immune-mediated cause of skin disease in multiple breeds of rabbits. The exact etiology is unknown, but often it develops secondary to another underlying health condition (eg: thymoma). Affected individuals have a non-pruritic flaky, scaly dermatitis with alopecia that originates around the head and neck and progresses caudally.
Diagnosis is by skin biopsy. Multiple treatment protocols have been tried, including prednisone, cyclosporine, isotretinoin/high dose vitamin A, fatty acid supplementation, phytosphingosine sprays/shampoos, and topical propylene glycol, but none have been uniformly successful. Many rabbits succumb to the condition or are euthanized due to the severity of signs.
The most common nodular skin tumors seen in rabbits are basal cell tumors, spindle cell sarcomas, collagenous hamartomas, papillomas, and mammary gland adenocarcinomas. Excisional biopsy is usually curative for the majority of these, although sarcomas may be locally invasive and mammary carcinomas have the potential to metastasize. More diffuse skin involvement is seen with cutaneous lymphoma, which manifests as thickened patches of skin, sometimes with alopecia, scaling, and crusting; pruritus is variable.
Diagnosis is via biopsy; localized cases may respond to radiation, but commonly the disease is multicentric and consideration should be given to chemotherapy, particularly patients with more aggressive or systemic signs. A diffuse exfoliative paraneoplastic dermatitis can occur secondary to thymic masses (thymomas) and occasionally other systemic diseases (hepatitis); presentation is very similar to sebaceous adenitis and some overlap is seen in the conditions histopathologically. Signs may improve with treatment of the underlying primary condition, where feasible.
Rabbits are one of the more commonly seen small exotic mammal species in general practice, thus a basic knowledge of the dermatological conditions that affect them is helpful. Stocking a few basic medications (Revolution, Advantage Multi, ivermectin, PPG, antifungals) will allow for the treatment of a variety of the more common skin conditions.
It is important to remember individual species’ drug sensitivities and the zoonotic potential of many infectious agents. Below are tables summarizing the most common skin conditions grouped by etiology with characteristic signs, treatment options, and drug doses.
Stay tuned to learn about dermatological diseases in rodents, including guinea pigs, hamsters, gerbils, rats, and mice!
Cathy Emery, DVM, is an Associate IndeVet practicing in Maryland and Virginia.
Topical Drug Details:
- Selamectin = Revolution (and comparable generics): ≤5lb puppy/kitten dose = 15mg = 0.25mL; 5.1-15lb cat dose = 45mg = 0.75mL; 15.1-22lb cat dose = 60mg = 1mL
- Revolution Plus is not currently recommended for use in small mammal species, as the safety of sarolaner is uncertain (despite fluralaner showing promise in rabbits and a few other exotics)
- Imidacloprid + moxidectin = Advantage Multi Feline, Barrier for Cats: 2-5lb dose = 23mg imidacloprid/2.3mg moxidectin = 0.23mL; 5.1-9lb dose = 40mg imidacloprid/4mg moxidectin = 0.4mL; 9.1-18lb = 80mg imidacloprid/8mg moxidectin = 0.8mL
- None of these are approved for use in rabbits, but are commonly used off label