Session #1004

Abstract

Dermatological conditions are common in exotic companion mammals. There are a large number of underlying causes including infectious (bacterial, viral, fungal, and parasitic), endocrine disease, conditions related to anatomy, conditions related to poor husbandry, and behavioral diseases. The resultant clinical signs of disease will vary with the underlying cause and can range from asymptomatic to severe pruritus with ulceration and erythema common with ectoparasites to severe alopecia in the absence of dermatitis, as is commonly seen in endocrine disorders. The diagnostic work-up will vary depending on the species, age, and clinical signs. Treatment is always aimed at the underlying cause in addition to any secondary consequences of the disease.

Introduction

Exotic companion mammals commonly present with dermatologic concerns to the exotic animal practitioner. The ideal approach to these cases involves a systemic diagnostic approach to allow the clinician to reach an accurate diagnosis and formulate a well thought out treatment plan. In all exotic species, husbandry plays an integral part in the pathogenesis of dermatological disease, which means that a detailed evaluation of husbandry is critical for successful management of the disease. In addition to husbandry issues, a variety of underlying causes of disease including infectious agents (bacterial, fungal, viral, parasitic), neoplasia, endocrine problems, behavioral problems, and underlying unique anatomy will also influence the occurrence of disease.

Normal Anatomy

Skin Structure and Function

The basic structure and function of the skin resemble that of the dog and cat. The skin is divided into a four-layered avascular epidermis, the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale. Underlying these layers is a structurally supportive, collagenous, and vascular dermis, followed by a subcutis consisting of connective tissue and fat (underneath the dermis). Rodents also have prominent brown fat stores that are located between the scapulae, in the ventral neck, in the axillary, and inguinal regions.¹

Hair Structure and Function

There are many types of hairs in exotic companion mammals. These include the primary (guard hairs) that are associated with sebaceous glands, apocrine sweat glands, and the arrector pili muscle. Rodents and ferrets lack apocrine sweat glands. There are also secondary (undercoat) hairs which are typically only accompanied by sebaceous glands. Tactile hairs are also present in many species.¹ Hedgehogs have modified hairs that are enlarged and stiffened to form spines that taper to a pointed tip. The spines have a thick outer layer of keratin, which is the same fibrous protein that makes up mammalian hair.

Footpad Structure and Function

The footpad is an area of specialized, thickened epidermis that has underlying shock-absorbing fat deposits. Atrichial (eccrine) sweat glands are only located in the foot pad.¹

Glands

Many small mammals have sebaceous scent glands which play an important role in scent marking and communication. Table 1 describes the location and appearance of the sebaceous scent glands in many common exotic companion mammals.¹

Table 1. Description of the location and appearance of the sebaceous scent glands in many common exotic companion mammals¹

Dermatologic Examination and Diagnostic Testing

A thorough husbandry history is essential to help determine either the underlying cause of the dermatological disease or factors that may be contributing to the disease. This will also aid in targets for diagnostics and treatment of the disease. Husbandry evaluation should include the type of housing, indoor or outdoor, substrate or bedding used, and a detailed diet review. Questioning the owner if the animal is pruritic, in addition to knowing if other animals or people in the house are affected, is also an important component of the history.

During the physical examination of the exotic companion mammal, a thorough and systematic evaluation should be performed. Depending on the species, temperament, and size, this may require sedation or anesthesia to obtain samples of diagnostic quality.

Below is a list of the commonly used diagnostic tests:

1.  Impression smears:

• Direct slide impressions provide the most utility in moist, exudative, or crusted lesions that will exfoliate or be picked up directly by the slide.
• Acetate tape impressions may be useful for lesions that are dry or for the detection of surface-dwelling ectoparasites.

2.  Skin scrapings:

• Skin scrapings are very useful for the diagnosis of ectoparasites. Depending on the type of parasite that is suspected, superficial or deep scrapings may be performed.
• Many exotic companion mammals have thin skin that can be easily damaged or torn with a scalpel blade, and often a skin spatula is used instead.

3.  Bacterial culture and sensitivity:

• Bacterial culture and sensitivity are useful when infection is suspected or an abscess is present. However, it should always be considered where the lesion is and what is being cultured to ensure that normal skin contaminants do not obscure the sample.
• Advanced testing for bacterial and fungal identification through the use of molecular-based DNA sequencing is also becoming more readily available.

4.  Fungal culture or identification. KOH preps still are useful for initial impression.

5.  Wood’s lamp:

• The Wood’s lamp has limited usefulness in exotic companion mammals, except for in ferrets, where Microsporum canis is most common. Rabbits and rodents are most commonly affected by Trichophyton mentagrophytes. Trichophyton mentagrophytes does not fluoresce under a Wood’s lamp.

6.  Trichogram:

• The trichogram is useful to evaluate the structure of the hair. When assessing a trichogram, the presence of broken or fractured hair ends can lead to the suspicion that the hair loss is traumatic. Additionally, trichograms may provide evidence of ectoparasites or the presence of fungal disease, such as dermatophytosis, by visualization of the fungal hyphae or ectothrix spores.
• Appropriate collection of hair samples is key to diagnosis. Forceps should be placed 1–2 cm from the scalp and hair (at the area of affected skin) and plucked firmly in the direction of natural hair growth. If the hairs are not plucked out firmly, they can appear as pseudo-dystrophic hairs and complicate the appropriate diagnosis.
• The hairs should be placed on a slide with a drop of mineral oil, in parallel, a cover slip placed, and evaluated with a microscope. Affected hairs will be covered in spores and penetrated by hyphae.

7.  Skin biopsies for histopathology.

8.  Clinical pathology testing (CBC, biochemistry):

• Routine bloodwork is useful for the assessment of the overall health of the patient, as well as to evaluate for any underlying systemic cause of the disease.

9.  Testing for adrenal disease in ferrets (ultrasonography, ±hormonal blood panel).

10.  Diagnostic imaging:

• Diagnostic imaging can be useful to help rule in or out an underlying systemic cause of disease.

Ferrets: Dermatologic Diseases

Anatomy, Physiology, and Husbandry Considerations

Ferret skin contains numerous sebaceous glands that are responsible for the slightly greasy hair coat, and the characteristic musky odor of ferrets.² The glands are larger when ferrets are intact because the production is under androgenic control. It is not recommended to routinely bathe ferrets in an attempt to remove the musky odor because it results in removal of their essential oils leading to pruritus and keratinopathies. Ferrets also have paired musk producing glands lateral to the anus, which are typically removed during early spay-neuter procedures in North America.² Most of a ferret’s odor comes from the dermal sebaceous glands, and therefore, it is important to note that removal of the musk glands does not remove the majority of their scent.³ Neutering can be beneficial to decrease the musky odor because it decreases androgenic stimulation.³

Hair Coat

Ferrets have a compound hair follicle arrangement consisting of one primary hair follicle and a collection of secondary hairs. The hair coat color of ferrets is defined by their coarse guard hairs. They also have a thick cream-colored undercoat which remains the same color throughout their life. The guard hair color can change, as can the facial mask. Typically, ferret hair coats become lighter as they age. Ferrets molt twice yearly (spring and fall) as a result of hormone-responsive changes in photoperiod. The hair coat thins with increasing daylight and temperatures, which corresponds with the normal ferret breeding season. Typically during a molt, ferrets develop bilaterally symmetrical alopecia of the tail, perineum, and inguinal area, or lose their guard hairs and will appear fluffy in appearance. The other molt occurs in the fall time but is less pronounced. The hair coat appears lighter in the fall and winter. Shaving ferrets at a time of seasonal hair loss can result in hair that takes weeks to months to regrow. As hair erupts in the ferret, a bluish appearance of the skin will result.³

Common Problems in Ferrets—General

Poor nutrition in ferrets can result in a dry, dull hair coat. Pruritus and flaky skin may be seen when the environment is dry. In the wild, ferrets counteract a dry environment by spending a considerable amount of time in underground dens that have high humidity.³

Infectious Diseases

Ectoparasites

Ferrets are susceptible to most of the ectoparasites that affect dogs and cats. Fleas and ear mites are the most common.

Fleas: Ctenocephalides species are usually involved (same as dogs and cats) in flea infestations of ferrets. Transmission occurs either with direct contact with another animal, or a flea-infested environment. Clinical signs of an infection with fleas may range from a ferret that is asymptomatic to a ferret with mild to intense pruritus, erythemic papules, and alopecia, particularly in the dorsal cervical, and interscapular area. Flea-bite hypersensitivity is not common, but when it occurs results in a pruritic papulocrustous dermatitis over the tail base, ventral abdomen, and caudomedial thighs. Diagnosis involves identification of fleas and flea excrement on the ferret. Advantage Multi® (Imidacloprid 10%, moxidectin 1%) is the only FDA approved treatment for ferrets. Other products, such as Revolution® (selamectin), are effective but are used off label. As with any species, flea treatment requires not only treatment of the animal affected, but treatment of the other animals in the house, as well as the environment.³

Ear mites: Ferrets are affected by the same ear mites as dogs and cats (Otodectes cynotis). These are transmitted directly from other infested animals. Clinical signs may range from asymptomatic ferrets to ferrets with severe scratching and head-shaking behaviors. In extremely severe cases, secondary otitis media or interna with neurologic deficits may occur, and a head tilt may be noted by the owner. Rarely, the mites will colonize other areas, especially the perineum. It is important to note that normal ferrets have dark brown, waxy debris in their ears, so this cannot be used as a clinical indicator of disease. Microscopic examination of the aural debris will provide a diagnosis. Treatment involves treating all animal in the house and requires gentle cleaning of the ears prior to treatment. Similar to fleas, Advantage Multi® and Revolution® are commonly used, with many other effective treatments described.³

Viral Disease

Canine distemper virus is a rare but very serious cause of dermatopathy in ferrets. The most common dermatologic areas affected include the chin and footpads. The disease causes a characteristic skin rash that is erythematous and pruritic, progressing to swollen and crusty skin that then spreads to the inguinal or perianal region. Hyperkeratosis of the foot pads is also a classic lesion. Additionally, the disease can cause a generalized dermatitis with orange-tinged skin that predisposes the ferret to secondary pyoderma. Neurologic and respiratory signs are also common and the disease is typically fatal in ferrets.³

Fungal Disease

Dermatophytosis is uncommon in ferrets, but the most commonly reported species is Microsporum canis. The disease is zoonotic and is more commonly seen in kits and young ferrets, or ferrets that are immunosuppressed for some other reason; however, in immune-competent ferrets, the disease can be seasonal and self-limiting. Typical lesions appear as small papules that spread peripherally resulting in large, circumscribed areas of alopecia and inflammation. Eventually, thickened, erythematous, and hyperkeratotic skin may result. Dermatophytosis is typically non-pruritic. Mycotic culture and/or histopathologic of a biopsy with PAS stain is diagnostic, but a Wood’s lamp can also be useful, as Microsporum canis will fluoresce. Various treatments have been described depending on the severity and range from topical treatments to systemic treatments. Complete treatment success is determined after two negative fungal cultures.³ Of important note, this disease is most commonly detected in ferrets that are housed around puppies or kittens, or in ferrets that are primarily coming from canine and feline shelter situations. This is an especially important consideration due to the zoonotic nature of the disease.

Bacterial Disease

Primary bacterial skin infections are uncommon in ferrets.

Cutaneous Neoplasia

A retrospective study that examined 574 cases of ferret neoplasia documented a 14% incidence of neoplasia of the integumentary system (the third common system affected). Benign lesions predominate these cases and include mast cell tumors, basal cell tumors, and sebaceous cell tumors.⁴

Mast Cell Tumors

Mast cell tumors (MCTs) in ferrets generally involve the skin and are benign, with visceral involvement and malignancy being very rare. MCTs in ferrets typically do not spread locally or metastasize. They are composed of well-differentiated mast cells and are often located on the head, shoulders, neck, and trunk. MCTs will appear as single to multiple raised, well-circumscribed hairless nodules that may appear hyperemic or may be ulcerated and covered with a black, crusty exudate. These lesions can be variably pruritic and erythematous. The tumors often wax and wane and change in appearance. Definitive diagnosis involves surgical biopsy and surgical resection is generally curative. New MCTs may develop in the same ferret over time.⁵

Basal Cell Tumors

Basal cell tumors, a type of epithelial tumor (epithelioma) arise from the pluripotential basal cells of the epidermis, are typically benign, and can develop anywhere on the body. They are the most common skin tumor of ferrets and appear as sharply defined, firm, white to pink lesions that are pedunculated to plaque-like and may also ulcerate. Definitive diagnosis and treatment require complete surgical removal. Metastasis with this tumor type has not been reported.⁵

Preputial Gland Tumors

Preputial gland tumors are malignant tumors arising from the apocrine glands of the prepuce, with carcinomas, adenocarcinomas, and cystadenocarcinomas reported. These neoplasms will start as very small skin or subcutaneous nodules near the preputial orifice, but very quickly grow and behave aggressively. These tumors can metastasize, commonly to the local tissues and lymph nodes. Treatment of these tumors requires early, wide, deep surgical excision, but may require penile amputation and urethrostomy to obtain clean margins.⁵

Endocrine Disease

Adrenal Gland Disease

Adrenal gland disease is a common cause of dermatopathy in ferrets and causes a progressive and persistent alopecia, often with pruritus. Adrenal gland disease can result in ferrets that have a strong odor due to androgenic stimulation of sebaceous glands in the skin. Definitive diagnosis requires measurement of adrenal androgen concentrations, though ultrasound may be useful to evaluate the appearance of the adrenal glands. Medical and surgical treatment options exist.⁶

Rabbits: Dermatologic Diseases

Bacterial Infections

Subcutaneous abscesses occur commonly in rabbits as a result of traumatic wounds, bacteremia secondary to apical infections of the teeth, oral foreign bodies, upper respiratory infections, and urinary tract infections. Abscesses in rabbits should be addressed by determining the underlying cause, in conjunction with treatment guided by bacterial culture and sensitivity. Anaerobic species of bacteria are often involved. Due to the caseous nature of rabbit purulent debris, en bloc removal is recommended, but not always feasible. Abscesses in rabbits do not typically drain well. Many treatment options have been described for rabbit abscesses including various packing and marsupialization techniques.

Moist Dermatitis

Moist dermatitis most commonly occurs on the chin, dewlap, and ventral neck (commonly referred to as “slobbers”), or perianally as a result of urine scald (commonly referred to as “hutch burn”). “Slobbers” often occurs as a result of excessive salivation secondary to dental disease or from water bowls or bottles that result in a constantly wet dewlap. “Hutch burn” typically occurs as a result of urinary disorders (bladder sludge, cystitis, urinary tract infection, urolithiasis), mobility disorders, reproductive disorders, and improper housing. Both scenarios require a complete diagnostic work-up to determine the underlying cause of the dermatitis. Similarly, treatment requires addressing the underlying cause as well as the dermatitis. Severe cases may require antibiotics and analgesia for the dermatitis.⁷

Ulcerative Pododermatitis (“Sore Hocks”)

Rabbits lack footpads and have thin skin. They only have coarse fur on their distal limbs.¹ During locomotion on proper substrate, the claws bear most of the weight, whereas during rest, the weight is distributed between the hind claws and the plantar aspect of the metatarsus. When rabbits are housed on improper substrate or are over conditioned, abnormal weight-bearing physiology occurs. The eventual result is a chronic, ulcerative, granulomatous dermatitis of the plantar metatarsal and volar metacarpal and phalangeal surfaces of the feet. The disease can progress to osteomyelitis and synovitis, and eventual superficial tendon displacement. Staphylococcus aureus and Pasteurella multocida are the most common bacteria identified in these lesions. Radiographs are important to determine if there is underlying bone involvement. Treatment involves correction of the underlying cause, relief of pressure on the affected areas, antibiotics dictated by culture and sensitivity, and analgesia to target pain and inflammation (opioids, NSAIDs, gabapentin). Body condition should also be addressed if the rabbit is overweight.⁸

Rabbit Syphilis

Rabbit syphilis is a contagious venereal disease caused by the spirochete Treponema paraluiscuniculi, and is transmitted between rabbits. The disease causes nonpruritic papules that tend to be erythematous and edematous and crusty ulcers at the mucocutaneous junctions of the lips, eyelids, nostrils, philtrum, vulva, prepuce, and perineum. Recovered bucks may have star-shaped scrotal scars and can remain carriers. Diagnosis can be achieved by identification of the corkscrew-shaped causative organism with dark-field microscopic examination of wet-mounted skin scrapings. Treatment is documented successfully with penicillin.⁹

Fungal Infections

Dermatophytosis (Ringworm)

Ringworm is a zoonotic disease that is most common in young rabbits. Trichophyton mentagrophytes is the most common species. Affected rabbits will demonstrate alopecic areas of the head, legs, and feet, with dry, crusty, and erythematous lesions. Similar to ferrets, culture and histopathology will aid in diagnosis. Trichophyton mentagrophytes does not fluoresce with a Wood’s lamp. Similar to other species, topical or systemic treatment is warranted depending on the severity of the disease.¹⁰

Parasitic Infections

Ear Mites

Ear mites in rabbits are a result of infection with Psoroptes cuniculi (rabbit ear mite), which is a large, obligate, non-burrowing parasite with a three-week life cycle. It is transmitted directly or by fomite involvement. Affected rabbits will have reddish-brown, bran-like crusting of one or both external ear canals, head shaking, ear drooping, and pruritus. Severe cases may spread down the ear canal and result in otitis media and otitis interna with associated neurologic signs. The mite can be identified with microscopic examination. Off-label treatment includes ivermectin and selamectin, among others. It is important to remember that fipronil is toxic and fatal to rabbits and should never be used.¹⁰

Fur Mites

Cheyletiella parasitovorax (rabbit fur mite) is a nonburrowing mite that lives on the keratin layer of the epidermis and is often referred to as “walking dandruff.” It is zoonotic to humans, as well as transmissible to other animals in the household. In an older rabbit that acutely develops disease, a primary problem causing immune suppression is likely present. Clinical signs can range from subclinical to a scaly, dry, and sometimes pruritic dermatitis with patchy alopecia and broken hairs. In severe infestations, the mites are visible to the human eye. The mite can also be identified with microscopic examination. Off-label treatment includes ivermectin and selamectin, among others. All rabbits in the house should be treated. If an older rabbit is affected with acute disease, investigation should be done before successful treatment can be accomplished.¹⁰

Fleas

Fleas most commonly affect rabbits housed with dogs and cats. Rabbits will present similar clinical signs and treatment as other species.

Myiasis

Cuterebra maggots: Cuterebra infect rabbits that are housed outdoors in warm weather. These parasites lay their eggs near the rabbit run and the larvae crawl through a natural orifice where they migrate to the subcutaneous site to pupate and create multiple swellings of the dorsum, axillary, inguinal, and ventral cervical regions. Each swelling encapsulates a single larva and has a breathing hole visible at the skin surface. Some rabbits will be unaffected, while others will become weak, anorexic, dehydrated, and lame from the pain, which can eventually lead to shock. Aberrant migration can occur to the nasal passages, eyes, sinuses, and ear canals through the central nervous system resulting in neurologic signs. Treatment involves the removal of the larvae. If the larvae rupture, anaphylaxis can occur. Antibiotics and analgesia should also be administered.¹¹

Noncuterebrid maggots: Maggots are attracted to moist areas, especially those with wounds. Common locations include matted hair around the perineum, face, and rump, especially in warm summer months of outdoor rabbits. Preexisting wounds are not necessary for maggot infection. Predisposing factors include perineal dermatitis (adherence of cecotrophs), urine scald, skin-fold dermatitis secondary to obesity, and inability to groom properly due to dental disease or arthritis. Rabbits often present with lethargy and anorexia, and eventually, skin necrosis and sepsis occur leading to shock. Treatment involves aggressive supportive care including wound management, analgesia, and antibiotics.¹¹

Viral Infections

Myxomatosis

Myxomatosis is caused by a myxoma virus in the family Poxviridae. The virus sticks to the mouthparts of biting arthropods when they probe through virus-infected epidermis (usually around the face and ears). It is then passively inoculated intradermally into a new host at a subsequent feed. The virus does not undergo replication within the vector. The natural host of this virus is the wild jungle rabbit, tapeti (Sylvilagus brasiliensis) in South America, with a similar, closely related virus, Californian myxoma virus, in wild brush rabbits (Sylvilagus bachmani) in California. In host rabbits, the disease results in mild, self-limiting cutaneous fibromas and no systemic disease. In domestic rabbits, myxomatosis results most commonly in the acute form of the disease, causing subcutaneous masses, swelling and edema of the eyelids and genitals, milky or purulent ocular discharge, pyrexia, lethargy, depression, and anorexia. Swelling of the head is a key lesion noted in this disease. Highly virulent strains can also result in deaths in the peracute form of the disease. Subacute myxomatosis has also been described. Overall, the disease has a high mortality rate in domestic rabbits, likely as a result of virus-induced immunosuppression and secondary septicemia. Outbreaks of disease are reportable. Vaccines are developed but are not commercially available in the US and require repeated boosters. Vaccination in the face of an outbreak is beneficial in limiting morbidity and mortality.¹²

Rabbit (Shope) Fibroma Virus

Shope fibroma virus is caused by a leporipoxvirus and infects many European wild rabbits and cottontails (Sylvilagus species). The virus is genetically and antigenically closely related to myxoma virus. The natural hosts, Eastern cottontail (Sylvilagus floridanus), Sylvilagus species (Sylvilagus bachmani, Sylvilagus nuttalli, and Sylvilagus audoboni), are refractory to infection. The virus is transmitted via biting arthropods. The virus results in large, flat, wart-like subcutaneous tumors of the face, feet, legs, and perineum in European rabbits (Oryctolagus cuniculus). The epidermis may become necrotic and slough or lesions may regress over several months. Supportive care can be provided to affected rabbits. Typically, rabbits do not have any systemic signs of disease. Vaccination with the myxomatosis vaccine provides some cross-immunity. Overall, the prognosis is excellent, except for suckling rabbits or immunosuppressed rabbits.

Rabbit (Shope) Papillomavirus

Rabbit (Shope) papillomavirus (cottontail rabbit papillomavirus) occurs in wild California brush rabbits (Sylvilagus bachmani) and cottontail rabbits (Sylvilagus floridanus). It is transmitted by biting arthropods. The virus results in rough, red, wart-like, keratinized, pigmented lesions of the ears, eyelids, neck, shoulders, abdomen, and thighs (areas of non-haired or thinly-haired skin). The normal process of keratinization is altered resulting in hyperkeratosis, parakeratosis, and fragmentation of the horny layer, giving a variable appearance to the lesions. The lesions may undergo immune-mediated resolution and disappear after months or progress to squamous cell carcinoma that metastasizes, commonly to the axillary lymph nodes. Domestic rabbits are more likely to progress to carcinoma lesions than wild rabbits.¹²

Cutaneous Neoplasia

Skin tumors unassociated with viral infection are uncommon in rabbits. Nonviral skin tumors that have been reported include squamous cell carcinoma, basal cell tumor, trichoepithelioma, trichoblastoma, sebaceous cell carcinoma, nonviral squamous papilloma, apocrine carcinoma, meibomian adenoma, sebaceous carcinoma, lipoma, liposarcoma, myxosarcoma, nerve sheath tumor, fibrosarcoma, leiomyosarcoma, leiomyoma, rhabdomyosarcoma, anaplastic sarcoma, and malignant melanoma.¹⁰

Skin Disease of Unknown Cause

Sebaceous Adenitis

Sebaceous adenitis causes a nonpruritic, scaly, and flaky dermatitis beginning around the neck and face, and progressing to diffuse skin disease. An infectious cause of the disease has not been identified, but an autoimmune T-cell mediated disease, lipid metabolism defects, and a concurrent link to thymoma have all been postulated. Histopathology can aid in diagnosis. Treatment has had limited success in rabbits, and frequently rabbits are euthanized because of the severity of the skin condition; however, successful therapy with cyclosporin and Miglyol has been more recently reported.¹⁰

Ehlers-Danlos-Like Syndrome or Cutaneous Asthenia

Ehlers-Danlos-like syndrome has been documented in rabbits and is suspected to occur as a result of mutations in collagen-forming genes or collagen-synthesizing enzymes leading to joint laxity, skin fragility, and skin hyperextensibility. The end result is rabbits with extremely fragile skin and slow-healing wounds. An effective treatment of the disease has not been described.¹⁰

Guinea Pigs: Dermatologic Diseases

Normal Anatomy

Guinea pigs have minimal or no hair between the nose and lips, around the lips, on the outer pinnae, and behind the ears.

Fungal Infection

Dermatophytosis

Young and immunosuppressed guinea pigs are most susceptible to dermatophytosis. Certain breeds of guinea pigs have been reported to be more sensitive to disease including purebred Teddy and Teddy Satins. The lesions appear as scaly, patchy lesions on the face, feet, and dorsum, circular areas of alopecia with inflamed and crusty edges, and occasionally pruritus. Trichophyton mentagrophytes is frequently involved, with Arthroderma benhamiae a growing concern in guinea pigs across North America, causing an aggressive and extremely transmissible form of the disease. Diagnostic work-up and treatment are similar to other species.¹³

Ectoparasites

Mites

Trixacarus caviae is a sarcoptic burrowing mite that results in a severe ectoparasitic dermatitis causing severe pruritus. This disease is zoonotic. The hallmark clinical sign is severe pruritus that may cause the guinea pig to appear to be seizing. Self-trauma and secondary fungal and bacterial infections are common. Diagnosis involves microscopic identification of the mite which requires deep skin scrapings due to the burrowing capacity of the mite. Ivermectin, selamectin, and other off-label treatments have all reported success. All guinea pigs in the house should be treated. If it is an older guinea pig with an acute mite infestation, a primary disease should be investigated before successful treatment can be accomplished.¹³

Chirodiscoides caviae (guinea pig fur mite) is the most common ectoparasite of guinea pigs and is often found clinging to the hair shaft in immunosuppressed or poor-condition animals. Guinea pigs affected by this mite will present with a rough hair coat, erythema, alopecia, scratching-induced dermatitis, and concurrent infestation with lice (Gyropus ovalis, Gliricola porcelli).¹³

Pododermatitis

Guinea pigs lack hair on their feet and metatarsal region. As in rabbits, their skin is relatively thin and adhered to the underlying tissues, so they are susceptible to local injury, ischemia, and pressure necrosis on the plantar and palmar surfaces of the feet. Improper husbandry, including wire bottom cages and abrasive and soiled bedding, often contribute to the lesions. Secondary bacterial infection with Staphylococcus aureus is common. The disease is most commonly seen in obese, adult guinea pigs. Guinea pigs with inadequate vitamin C in their diet are predisposed to disease. The diagnostics and treatments are similar to rabbits, with the addition of vitamin C supplementation.¹³

Hormonal Alopecia

Hormonal alopecia occurs in female guinea pigs with ovarian follicular cysts. Ovarian cysts are common in sows between three months and five years of age, with guinea pigs aged 2–4 most commonly affected. The cysts typically increase in size with age. The most common clinical signs include progressive hair loss over the flank and abdomen without pruritus or an abnormal appearance to the skin. Crusting of the skin around the nipples, a pear-shaped body conformation, mounting, aggression, and other sexual behaviors are also reported. The cysts create a space-occupying lesion that can result in hyporexia to anorexia, lethargy, and vocalization when handled. Some guinea pigs never demonstrate signs of disease. At this time, ovariohysterectomy is the treatment of choice. Various medical therapies have been attempted with varied success. Hormonal alopecia has also been reported in late pregnancy and lactating sows.¹⁴

Cutaneous Neoplasia

Most of the reported cutaneous tumors in guinea pigs are benign.¹³

Trichofolliculomas

Trichofolliculomas are the most common tumor of guinea pigs and are a benign skin tumor of the hair follicle. Most commonly, these tumors are noted on the dorsal rump and caudal hip area, incorporating the scent glands. Trichofolliculomas can become large, malodorous, exudative, and ulcerated, and may even rupture with a white or gray, thick sebaceous discharge. Complete excision is usually curative.¹³

Other Tumors

Other skin tumors commonly described in guinea pigs include lipomas and trichoepitheliomas.¹³

Chinchillas: Dermatologic Diseases

Dermatophytosis

Similar to other rodents, Trichophyton mentagrophytes is the most common cause of dermatophytosis in chinchillas. Chinchillas commonly present with patchy alopecia on the nose, behind the ears, and on the forefeet. Diagnosis and treatment are similar to other species.¹⁵

Fur Chewing

Fur chewing is a common problem of chinchillas, especially in breeding facilities, or pet chinchillas suffering from dental disease. It is suspected to be a maladapted displacement behavior as a result of stress. Chewed fur may be noted most commonly on the dorsum from the lumbar area to the tail, and laterally on the flanks. Diagnostics should be performed to rule out painful conditions. Treatment involves the management of any painful conditions and reducing stress in the household.¹³

Pododermatitis

Pododermatitis predominantly affects the hind feet of chinchillas. Similar to other species, lesions can range from mild to severe with osteomyelitis.¹⁵

Fur Slip

Though not inherently a disease process, fur slip is a defense mechanism in chinchillas, where they will automatically release large patches of fur when they are mishandled or grabbed only by their fur. In the wild, chinchillas use this mechanism to escape predators when they are captured.

Mice: Dermatologic Diseases

Nearly all problems seen in pet mice are associated with the skin. There are four groups of skin problems in mice:

1.  Behavioral disorders

2.  Husbandry-related problems

3.  Microbiologic and parasitic infections

4.  Idiopathic conditions

Behavioral, husbandry, and infectious causes of skin disease provide a straightforward diagnosis and treatment, but many skin diseases in mice are characterized as idiopathic resulting in chronic, ulcerated skin, often with secondary bacterial infections. Idiopathic skin diseases tend to be poorly responsive to treatment, and frequently these animals are euthanized as a quality-of-life concern.¹⁶

Behavioral Disorders

Barbering, Fur/Whisker Trimming/The Dalila Effect

Social dominance in mice is demonstrated as barbering and fighting. The dominant mouse chews off the whiskers and hair surrounding the muzzle and eyes of its cage mates. The mouse responsible for barbering will remain fully furred. If the dominant mouse is removed to prevent barbering, reshuffling of the hierarchy occurs, and another mouse will take on the dominant role. Some theories propose that the behavior may not be due to dominance and other factors, such as genetics, are thought to play a role. The skin itself will appear normal. Environmental enrichment has been shown to delay the onset and reduce the overall prevalence of barbering.¹⁶

Husbandry-Related Problems

Alopecia

Mice will self-traumatize their facial region with mechanical abrasion on the cage bars, metal feeders, or metal watering devices. This will result in small patches of alopecia on the lateral surface of the muzzle.¹⁶

Microbiologic and Parasitic Infections

Alopecia and dermatitis due to infectious causes in mice are most commonly associated with fur mites. Ectoparasites are common in mice purchased from pet stores and result in thin hair, especially in the difficult to groom areas. Clinical signs include a greasy coat, pruritus, and self-inflicted dermal ulcerations.¹⁶

Idiopathic Conditions

Certain laboratory strains have demonstrated increased occurrence of these diseases, suggesting there may be a genetic component.

Idiopathic Ulcerative Dermatitis

Idiopathic ulcerative dermatitis is a severe inflammatory skin disorder of unknown cause. Certain strains of inbred mice have been documented to be affected more commonly. Mice demonstrate severe pruritus characterized by self-mutilation, dermal ulceration, necrosis, and fibrosis. As the disease progresses, the lesions develop from superficial excoriations to deep, necrotic ulcerations with serocellular crusts. The lesions are also associated with a marked inflammatory response. Most commonly, the dorsal scapular region is affected, but the torso, shoulder, head, and face can also be affected. Many factors have been proposed for the management and treatment of the disease, but no single treatment has documented successful resolution. The goal is to reduce the severity of the lesions. Toenail trimming has been reported to have high success in reducing the clinical signs associated with the lesions.¹⁶ Both gabapentin and maropitant citrate have also shown promise as potential treatments for this disease.^17,18

Progressive Necrosing Dermatitis of the Pinna

Similar to idiopathic ulcerative dermatitis, progressive necrosing dermatitis of the pinna is also reported in mice. This disease occurs in outbred mice and no strain background association has been documented. The initial lesion on the dorsum of the pinna resembles an engorged blood vessel or slight erythema which progresses to oozing serum, necrosis, and eventual loss of part of the pinnae.¹⁹

Cutaneous Neoplasia

Mammary Neoplasia

Mammary adenocarcinomas are extremely common in mice, but their incidence does vary according to mouse strain and the presence or absence of mouse mammary tumor viruses. These tumors in mice are typically malignant and carry a poor prognosis.¹⁶

Rats: Dermatologic Diseases

Ectoparasites

Ectoparasites are more common in rats than mice. A variety of mites, including Radfordia enisfera (fur mite), and Ornithonyssus bacoti (tropical rat mite), and lice (Polyplax serrata, Polyplax spinulosa), have all been reported.¹⁶

Neoplasia

The most common subcutaneous tumor in the rat is fibroadenoma of the mammary glands. In rats, the distribution of mammary tissue is extensive and can occur anywhere from the neck to the inguinal region. Tumors can be large and occur in both males and females. Adenocarcinomas are less common tumors of rat mammary tissues. Frequency is lower in ovariectomized and neutered rats when performed at a young age. Surgical removal is palliative, as often new tumors occur (unrelated to the initial tumor), necessitating multiple surgeries for the space-occupying masses.¹⁶

Hamsters: Dermatologic Diseases

Flank Organs

Syrian hamsters possess paired flank organs in the costovertebral area. These flank organs are androgen-dependent and consist of sebaceous glands, pigmented cells, and terminal hairs. The glands are larger and heavily pigmented in males and are used for territorial marking. Melanoma of the flank organs has been reported in Syrian hamsters commonly, with males 10 times more likely to be affected than females.²⁰

Demodex

Demodex caused by Demodex criceti and Demodex aurati have commonly been reported in hamsters, especially secondary to immunosuppression and underlying disease. Diagnosis of Demodex in a hamster should immediately trigger investigation for an underlying disease process.²⁰

Gerbils: Dermatologic Diseases

Facial Eczema, Sore Nose, Nasal Dermatitis

Nasal dermatitis is a common lesion of gerbils that presents with erythematous nares. The disease progresses to a localized alopecia and eventual extensive moist dermatitis. The disease is suspected to be a result of increases in the secretion of porphyrins by the Harderian gland which behaves as a skin irritant and is exacerbated by bacterial infection. The disease is commonly seen in situations of overcrowding and high humidity. Treatment requires alterations to humidity, antibiotics for secondary infection, analgesia, and provision of sand baths once healing progresses.²⁰

Tail Slip

Gerbils experience tail slip when they are picked up by their tail. The exposed tail is raw and becomes necrotic and sheds off. When this occurs, surgical amputation of the tail is required proximal to the location of the slip.²⁰

Abdominal Marking Glands

Gerbils have large ventral abdominal marking glands that can be mistaken for tumors; however, infection and neoplasia, often malignant adenocarcinoma, of this gland can also occur.²⁰

Sugar Gliders: Dermatologic Diseases

Stress-Related Disorders

Sugar gliders are highly prone to stress in captivity and this can manifest in dermatologic presentations including self-mutilation, coprophagy, hyperphagia, polydipsia, and pacing. Proper nutrition, hygiene, housing, and social groupings are required to try to mitigate stress in sugar gliders in captivity.²¹

Self-Mutilation

Self-mutilation of the tail, limbs, scrotum, and penis is a common presentation of sugar gliders that is suspected to occur as a result of lack of proper socialization with other gliders, disregard to nocturnal nature, poor husbandry, and inappropriate nutrition. Pain or neurasthenia are also suspected as a possible cause, as self-mutilation is common in sugar gliders in the post-operative period.²¹

Endocrine Alopecia

Endocrine alopecia has been reported in older, female sugar gliders, resulting in a bilaterally symmetric alopecia. An etiology of the disease has not been documented.²¹

Hedgehog: Dermatologic Diseases

Mites

Numerous mite species have been reported in hedgehogs, with Caparinia tripilis the most common. Other mite species include Caparinia erinacei (most common in wild African hedgehogs) and Notoedres sp. Some hedgehogs are subclinical, but others may present with hyperkeratosis, seborrhea, spine loss, white or brownish crusts (mite droppings) at the base of spines and around eyes, pruritus (only in some), lethargy, and decreased appetite.²²

Ear Mites

Notoedres cati is the causative agent of ear mites in hedgehogs and results in clinical signs of crusted lesions around the head and ears, accumulation of waxy, otic debris, and otic pruritus.²²

Fungal Infections

Dermatophytosis is also reported in hedgehogs with causative agents including Trichophyton erinacei, Trichophyton mentagrophytes, and Microsporum species. Disease results in a crusting, non-pruritic dermatitis around the face and pinnae. Diagnosis and treatment are similar as for other species.²²

Skin Neoplasia

Skin neoplasia is common in middle-aged to older hedgehogs, with a variety of different types described including papilloma, squamous cell carcinoma, lymphosarcoma, sebaceous gland carcinoma, and osteosarcoma of the skin.²²

References

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