Pruritus

Parasites

Psoroptes cuniculi (rabbit ear mite): This parasite causes otitis externa and rarely otitis media which can result in neurologic signs.^2,3 Rabbits will present with head shaking, pruritus of ears and head and/or ear dropping (this may be the initial sign). Pinna and canals will be erythematous and will have a thick crust which is often red-brown in color. Other parts of the body may be affected. Do not attempt removal of crusts as this is quite painful! Use systemic anti-parasiticides.

Trixacarus caviae: T. caviae infestation should be considered as the first differential for any pruritic guinea pig.^6,7 Convulsions resembling seizures can be seen in infested guinea pigs due to the intense pruritus and debilitation experienced by some affected animals.

Notoedres muris: Notoedric acariasis in hamsters affects mainly the ears, face, genitalia and tail. The diagnosis can be made by distribution and characterization of the clinical signs and by performing skin scrapings. Rats affected by notoedric acariasis resemble hamsters clinically, except that they sometimes present with nasal 'horns.'⁸ Frequently the mite can be visualized when performing a skin scrape of this nasal hyperkeratotic lesion.

Lice are usually seen in small numbers in rabbits and rodents. Large numbers may indicate an infestation with another skin parasite, or an underlying systemic disease (hypovitaminosis C in Guinea pigs, for example). Polyplax serrata (mice) and Polyplax spinulosa (rats) may serve as vectors for Mycoplasma (Haemobartonella) muris, Encephalitozoon cuniculi, and Eperythrozoon coccoides.

Diagnoses of these parasitic disorders can be confirmed by finding the parasites on multiple skin scrapings. Medical grade spatulas are safe and easy-to-use instruments to perform the scrapings. Example: Fisherbrand^TM Microspatula with Flat-Ended Blade, catalogue number 21-401-20, Fisher Scientific; http://www.fisherscientific.com.

Treatment

Ivermectin: 0.2 to 0.4 mg/kg q 2 weeks for 2 to 3 treatments PO or SQ. Ivermectin should not be administered orally to guinea pigs due to difficulties with GI absorption.⁹ For Notoedres muris in hamsters and rats: ivermectin 0.5 mg/kg administered q 1–2 weeks PO, SQ or in the form of a pour-on solution for at least 8 weeks is recommended.^8,10 In rabbits, ivermectin has been used to treat Cheyletiella infestations in doses ranging from 0.2–2.1 mg/kg SQ q 11 days x 3 or 0.6–2.7 mg/kg PO q 10 days x 3.¹¹

Selamectin (Revolutionâ, Strongholdâ, Zoetis): in rabbits for the treatment of ear mites 6 or 18 mg/kg twice, 28 days apart.¹² For Cheyletiella at 6.2–20.0 mg/kg q 2–4 weeks x 1–3¹¹ or one dose of 12 mg/kg¹³. Guinea pigs: 12 mg/kg.

Imidacloprid/moxidectin (Advocate®, Advantage Multi®; Bayer): for ear mites, applied 3 times, 30 days apart.¹⁴ Imidacloprid (Advantageâ, Bayer) should be effective against lice (but not mite) infestation.

Do not use fipronil (Frontlineâ/Frontlineâ Plus, Merial) in rabbits (or hedgehogs) as its use has been associated with fatalities;² there may be adverse effects from the spray form in hedgehogs, due to their predisposition for respiratory problems and tendency to roll into a ball (with nares close to the sprayed skin).

Topical lime sulfur (sulfurated lime, Dechra, Overland Park, KS 66211 USA): for lice at 1:32 dilution with water.

Fleas: Domestic rabbits are often exposed to fleas Ctenocephalides sp. when they share the household with a dog or cat.^2,3 In pet rabbits housed outside or exposed to wild rabbits, various flea species may be found including the rabbit flea Spilopsyllus cuniculi (common in rabbit colonies). S. cuniculi is an important myxomatosis vector. S. cuniculi often bites on the pinnae and face, and may bite cats and dogs. Pruritus is variable in rabbits. Imidacloprid (Advantage®, Bayer), has been shown to be effective in flea control in rabbits, and is licensed for this in the UK.³

Alopecia Without Pruritus

Dermatophytes

The usual dermatophyte species affecting rabbits and rodents are Trichophyton mentagrophytes, Microsporum canis, and M. gypseum. T. mentagrophytes is common in laboratory colonies, pet shops, etc., but M. canis more common in house pets. Clinical signs may also include scales, crusts and erythema.

Diagnosis: fungal culture (most accurate), direct examination of hair (trichogram) or scales mounted in 10% KOH or mineral oil (often non-diagnostic), Wood's lamp (only positive in 50% [?] of M. canis infections).

Treatment of dermatophytosis:^2,3,6,8

 Itraconazole 5–10 mg/kg daily, for 1 month, although the drug is probably safe for up to 3 months.

 Terbinafine 10 mg/kg for 2 to 6 weeks, a suspension in water or syrup.

 Griseofulvin 15 to 25 mg/kg for 4 weeks. Avoid in pregnant animals (teratogenic).

 Lime sulfur topical 1:32 dilution with water 2–3 times weekly - sole treatment or adjunctive.

 Enilconazole (Imaveralâ, Janssen - not available in USA) 2 times weekly is effective; however, rabbits and rodents are frequent groomers and may ingest too much of the medication.

Clipping is not recommended due to difficulties and stress. The environment should be disinfected (discard bedding, wash cages in lime sulfur, etc.).

Demodicosis

This is most common in Syrian hamsters (Mesocricetus auratus) which have two species: Demodex aurati - in hair follicle and Demodex criceti - on/in stratum corneum. Clinical signs are non-pruritic alopecia and scales along the dorsum, hindquarters and abdomen. The disease is more common in older animals and associated with stress, underlying illness or immunosuppression. Infestations with D. criceti may be more pruritic. Diagnosis is via skin scrapings: D. criceti may be difficult to find.

Treatment

Ivermectin at 0.3 mg/kg SQ q 7 to 10 days or PO q 24 hours has been reported effective.⁷ Treat until resolved and look for underlying diseases. Topical lime sulfur (1:32 dilution with water, twice weekly for 6 treatments) may be effective against D. criceti.

Endocrine

Hyperadrenocorticism

Most common in hamsters, both pituitary dependent and adrenal tumor forms noted. Skin hyperpigmentation, polyuria, polydipsia and polyphagia can be seen. Consistently effective treatment has not been described.⁷ Recently a Guinea pig was treated successfully with trilostane at 2–4 mg q 24 h.²¹

Cystic Ovaries

Most common in guinea pigs and associated with hyperestrogenism. Alopecia affects the flanks symmetrically and bilaterally. Enlarged abdomen is common. Age: 1.5–5 years. Ovariohysterectomy is preferred treatment.⁶

Scaling and Crusting

Cheyletiella sp (non-burrowing mites)

Cheyletiellosis in rabbits is a common cause of scaly dermatosis. It is zoonotic and contagious to other animal species such as dogs and cats.

Diagnosis is by finding mites on skin scrapings or acetate tape preparations.

Treatment: Selamectin same as for Psoroptes cuniculi.

Treponema paraluiscuniculi causes venereal spirochetosis (rabbit syphilis). Clinical signs include crusts, erythema, edema, papules, vesicles, ulcers and proliferative lesions localized to the face and perineum. Sneezing was observed in 33% of cases with nasal lesions.²² In cases of maternally acquired infection, lesions could be initially found mainly on the face. Lesions are painful but not pruritic. The disease may be associated with metritis, abortion and neonatal death. Rabbit syphilis is not zoonotic.

Diagnosis is by microscopic visualization of T. cuniculi from skin scrapes on dark field microscopy, or special silver stains to demonstrate the organisms on biopsy. Serologic tests to diagnose human syphilis can be used.

Treatment

Penicillin G at 40,000 to 80,000 IU/kg SC, weekly for 3 treatments. It is very important to monitor for signs of associated antibiotic enterotoxemia. Treat all in-contact rabbits.^2,3,23 Alternatives: chloramphenicol 55 mg/kg q 12 h for 4 weeks²³ or azithromycin 30 mg/kg/day given orally 1–2x q 24 h for 15 days²⁴.

Sebaceous adenitis has been reported in domestic rabbits as a cause of alopecia and non-pruritic scaly dermatosis.²⁵ Diagnosis is by biopsy. Successfully therapy has included cyclosporine and a medium-chain triglyceride supplement^27a with or without a shampoo, spray and spot-on containing the pro-ceramide phyosphingosine.^27b

Cutaneous lymphoma has been reported in hamsters, rabbits, mice and gerbils.^28-30

Myxomatosis is caused by a myxoma (pox) virus transmitted by arthropod vectors, or through physical transport. New World rabbits are resistant to this disease, but Old World rabbits are extremely susceptible (pet rabbits are Old World rabbits).^2,3 There are various strains of this virus.³⁶ Clinical signs in peracute and acute cases are edema of the head, ears, eyelids and genitalia and milky oculonasal discharge. Firm non-pruritic and erythematous nodules (myxomas) are usually associated with less virulent strains and develop at the site of infection. Lethargy, fever and anorexia can be present. Morbidity and mortality are high in pet rabbits, approaching 100%. The incubation period is from 8–21 days. The diagnosis is by clinical signs, microscopic lesions and virus isolation. Supportive treatment, vector control, and a preventative vaccine (not available in USA) may be offered/discussed with the owner; the prognosis is grave.^2,3

Nodular Dermatoses

Trichofolliculoma seem to be the most common neoplasia, and in hamsters, is associated with a polyoma virus.³⁴

Pododermatitis ("Sore Hocks")

Rabbits

Ulcerative pododermatitis is a chronic ulcerative granulomatous dermatitis of the metatarsal area seen in mainly in overweight inactive rabbits kept on wet bedding, grid floors, rough cages and/or unsanitary conditions. Hereditary factors may be involved; Rex rabbits are particularly affected as they lack guard hairs. The most common secondary bacteria is Staphylococcus aureus. Lesions are bilateral, plantar aspect of metatarsal area with progression of erythema, hyperkeratosis, crusts, pus, necrosis, osteomyelitis and septicemia. Treatment is difficult, based on correction of predisposing conditions, surgical drainage, topical antimicrobials, surgical dressings, and systemic antibiotics (based on culture and sensitivity). Enrofloxacin (5–15 mg/kg subcutaneously q 24 h) may prove helpful in early. Antibiotic-impregnated methylmethacrylate beads are reported as helpful. The earlier this disease is addressed, the better the chances of successful treatment.^2,3 Pain management is important; meloxicam (0.1–0.5 mg/kg PO q 12–24 h) or tramadol (10 mg/kg PO q 24 h) may be used.³⁵

Guinea Pigs

Ulcerative pododermatitis is relatively common in guinea pigs. S. aureus is generally isolated, although Corynebacterium pyogenes may be found. Predisposing factors: obesity, poor hygiene, hypovitaminosis C, and wire flooring. Lesions are bilateral, on the plantar aspects of the metacarpal and metatarsal areas with progression as in rabbits. Treatment: topical antiseptics (silver sulfadiazine or mupirocin), systemic antibiotic therapy (enrofloxacin) and bandaging, plus addressing the underlying cause. Treatment is often unsuccessful, and systemic amyloidosis often occurs with chronic infection.^6,7

References

References are available by request.