CHAPTER | 15 Avian and Exotic Animal Dermatology
Common mites of avian and exotic animal pet species are generally species specific (Table 15-1). Fur mites generally cause dandruff and patchy alopecia with little associated pruritus. The rabbit fur mite (Cheyletiella parasitovorax) is considered zoonotic, causing mild hyperemia and pruritus in humans. The ear mite, Otodectes cynotis, is commonly found in ferrets and can spread between cats and ferrets; therefore it is important to treat all susceptible pets in the household. The presence of black earwax in ferrets does not necessarily denote ear mite infestation. The rabbit ear mite, Psoroptes cuniculi, can cause such an accumulation of dry crusts that an upright ear can be weighted down into the lop-ear position. Demodex spp. are commonly demonstrated in hamsters greater than 2 years of age with concomitant Cushing’s disease. Hamsters are generally exposed to the mites when young but do not exhibit clinical signs until immunocompromised. Rabbits and guinea pigs with intense pruritus should be checked for their respective mites because this would be the most common differential. Birds, typically budgerigars and canaries, infected with Knemidokoptes generally show pitting of the beak and facial skin (budgerigars), or pitting of the skin of the legs (canaries). Snake mites (Oophyionysus spp.) can be found anywhere on the snake’s body, but typically they can be found around the eye or between the cleft of skin under the chin. Severe infestations in snakes can cause significant anemia. African hedgehogs kept as pets in the United States can present with Chorioptes spp. mites, resulting in quill loss and skin crusting and flaking.
|Myobia musculi||Found over head, neck, and shoulder area|
|Myocoptes musculinus||Found over entire body|
|Cheyletiella parasitovorax||“Walking dandruff mite,” zoonotic|
|Psoroptes cuniculi||Dry crusts in ear canal and pinna|
|Otodectes cynotis||Dark, waxy discharge in ears|
|Notoedres notedres||Found over ears, nose, feet, and anus|
|Hamster||Common secondary to Cushing’s disease|
|Demodex criceti||Found in epidermis|
|Demodex aurati||Found deep (hair follicles, sebaceous glands)|
|Trixacarus caviae||Marked purities: neck, shoulder, inguinal|
|Chirodiscoides caviae||Nonpruritic: lumbar, lateral rear limbs|
|Sarcoptes scabiei||Intense pruritus, self-mutilation|
|Budgerigars and Canaries|
|Knemidokoptes pili||“Scaly leg and face mite,” pitting beak, skin|
|Ophionyssus natricis||Check crypts around eye and cleft under chin|
|Chorioptes spp.||Quill loss; skin crusting and flaking|
In general, the treatment for mites in most species is ivermectin at 0.2 mg/kg PO, SC, or preferably topically repeated in 10 to 14 days, with some important exceptions: never use ivermectin in turtles or tortoises—it can cause paralysis, coma, death as a result of their permeable blood-brain barrier; never inject ivermectin into birds, especially small birds, as the propylene glycol base can cause an anaphylactic reaction and death.
FIGURE 15-3 Acariasis.
FIGURE 15-4 Acariasis.
FIGURE 15-5 Acariasis.
FIGURE 15-6 Acariasis.
FIGURE 15-7 Acariasis.
FIGURE 15-8 Acariasis.
The mouse louse (Polyplax serrata) is common in wild mice, causing anemia, debilitation, and intense pruritus. If it is found in pet mice, there is usually exposure to wild mice. The spined rat louse (Polyplax spinulosa) is rare but can cause pruritus, irritability, and anemia. The lice of guinea pigs (Gliricola porcelli, Gyropus ovalis) are commonly seen in pet guinea pigs, and if heavy in number can cause pruritus, rough hair coat, and alopecia. Typically, infestation with Gyropus spp. is associated with intense pruritus. Bird lice are uncommonly seen in pet parrot-type birds but are commonly seen in backyard poultry and peafowl. The chicken head louse (Cuclotogaster heterographus) is found about the head of chickens and peafowl. The chicken body louse (Menacanthus stramineus) is found near the vent of a variety of domestic fowl, including chickens, peafowl, guinea fowl, quail, pheasant, ducks, and geese.
In general, the treatment for lice is ivermectin at 0.2 mg/kg PO, SC, or topical, except for these important exceptions: never use ivermectin in turtles or tortoises—it may cause paralysis, coma, or death because of their permeable blood-brain barrier; never inject ivermectin IM into birds, especially small birds, as the propylene glycol base can cause an anaphylactic reaction and death. Other susceptable animals in the group should be treated as well as the environment.
FIGURE 15-10 Pediculosis.
FIGURE 15-11 Pediculosis.
Recently imported parrots may occasionally have a subcutaneous mass of adult Pelicitus spp. nematodes. Recently imported reptiles, including day geckos, may have a coelomic or SC mass of adult Thamagadia or Magnathamagadia spp. Rabbits that graze outside or are fed fresh-cut grass from outside can get Cuterebra spp. bot larva subcutaneously. The Cuterebra is ingested and migrates out of the oral cavity or esophagus to a subcutaneous site and is distinguished by the presence of a breathing hole in the skin.
In reptiles and birds, the roughly 1 × 1-cm SC mass may have a vermiform shape. In rabbits, the roughly 4 × 2-cm SC mass will have a tell-tale breathing hole, and sometimes movement can be observed through the breathing hole under the skin.
FIGURE 15-13 Subcutaneous Parasites.
Maggots are seen most commonly in the perineal area of rabbits housed outdoors and wild bird patients after trauma. A variety of ticks can infest domestic rabbits housed outdoors or wild rabbits. Fleas are occasionally seen in rabbits and ferrets, with ferrets seeming particularly susceptible to heavy infestations and subsequent fatal anemia. Pruritus is generally mild.
FIGURE 15-15 Myiasis, Flea or Tick Infestation.
This sexually transmitted disease of rabbits causes crusting and erosive lesions of the skin and mucocutaneous junctions of the perineum, periocular and perioral areas, and sometimes the base of the ear. This disease is NOT zoonotic; human syphilis is caused by T. pallidum. The incubation period is long, approximately 3 to 6 weeks. Males without obvious signs can transmit the disease.
Differentials include acariasis (see Figure 15-3) and papillomavirus, (see Figure 15-45), which typically involve other areas of the body than the mucocutaneous junctions.
Diagnosis is often based on typical clinical signs and response to treatment, but a definitive diagnosis can be obtained by identifying the organism on biopsy or via direct microscopic examination of the fluid obtained after removing superficial crusts and squeezing the skin. After a few drops of saline are added and the condenser is turned down on the microscope, the motile bacteria can be seen.
Sometimes this is a self-limiting disease. If the rabbit is to be bred or the lesions are troublesome, then treatment is recommended with procaine penicillin G with benzathine given subcutaneously ONLY every 7 days for 3 treatments. Remember never to give rabbits oral penicillin as this may cause fatal enteritis.
FIGURE 15-17 Rabbit Syphilis.
FIGURE 15-18 Rabbit Syphilis.
The causes of ulcerative pododermatitis in rabbits include obesity, genetically sparse hair cover over the plantar surface of the “hock” (actually the plantar surface of the proximal metatarsus), and trauma from wire-only substrate or carpet, causing shearing forces on the hair. The hair provides the cushion for the plantar surface. Mild pododermatitis includes alopecia and hyperemia of the intact skin. Moderate pododermatitis involves breakdown of the skin with erosions, scabs, proliferative tissue, and swelling or infection of skin. Severe pododermatitis with osteomyelitis can easily occur because there is very little soft tissue coverage in this area. Guinea pigs present with this same disease, but the cause is usually unsanitary conditions past or present, and it is very difficult to treat.
Captive raptors commonly present with pododermatitis because they stand most of the day. It has been shown that during flight, the temperature and blood supply to a raptor foot increase dramatically. The plantar surfaces of the digits and tarsometatarsal area are more commonly affected in raptors, passerines and small psittacines, whereas parrots are usually affected on the plantar surface of the tarsometatarsus. Small or uniform-size perches, hypovitaminosis A, obesity, and “sitting back on the hocks” are usual causes in pet parrots.
Mild pododermatitis of rabbits can be improved with changes in husbandry, such as providing a flat place to stand (kitchen cutting boards work well), removing wire substrate, limiting or eliminating time on carpet, providing towels or hay, or making a “bunny bootie” to bandage or somehow cover and protect the proximal metatarsus. The prognosis is good for mild pododermatitis. Moderate to severe cases may require surgery to remove abscessed areas, multiple days of flushing an infected joint, and antibiotics (based on aerobic and anaerobic culture). The prognosis is guarded to grave for moderate and severe pododermatitis, respectively. Enrofloxacin is a safer antibiotic for use in rabbits; it provides good bone penetration but is not effective against anaerobic bacteria. Metronidazole is typically used in rabbits if Fusobacterium necrophorum or a similar organism is cultured. If anaerobic bacteria is cultured, such as Fusobacterium necrophorum, then metronidazole is typically used in rabbits, or subcutaneous Procain Pen G. Remember, do not give penicillins orally to rabbits as it can be fatal.
The very chronic form of pododermatitis in Guinea pigs requires improved substrate, soaking feet in warm water to increase circulation, frequent cleaning and moisturizing of feet, and long-term antibiotics.
Birds with mild pododermatitis may improve with husbandry changes such as a wider perch, a perch with varying diameters, a padded perch, improved diet with less fat or fewer calories or with needed vitamin A, and, most important, increased exercise. If infection is present, then surgery or long-term antibiotics based on culture (both aerobic and anaerobic) and bandaging may be necessary. A variety of bandages have been described, such as “ball,” where the foot is bandaged into a ball; “snowshoe,” where the bandage is flat-bottomed to disperse the weight over a larger surface area; or a bandage that puts no weight on the bottom of the foot because a U-shaped bar is strapped to the leg. The prognosis is guarded to grave for moderate and severe pododermatitis, respectively.
FIGURE 15-20 Ulcerative Pododermatitis.
FIGURE 15-21 Ulcerative Pododermatitis.
FIGURE 15-22 Ulcerative Pododermatitis.
FIGURE 15-23 Ulcerative Pododermatitis.
Mycobacteriosis caused by Mycobacterium avium, Mycobacterium genovense, and other species has been described periodically in parrots. A rare cutaneous form has been described and presents as nonhealing raised lesions over the legs that do not heal or respond to typical antibiotics. The typical form of mycobacteriosis in birds generally affects the hepatic and gastrointestinal (GI) systems.
A histopathologic diagnosis of a chronic granulomatous lesion with no obvious organisms should be suspicious of mycobacteriosis and further testing should be pursued. Mycobacteria spp. can be detected on special stains of a biopsy sample. Specifically, a Fite’s modified acid-fast stain should be requested because a regular acid-fast stain may destroy the delicate types of mycobacterial species that infect birds. A PCR test can also be performed on tissues.
Euthanasia, not treatment, is recommended because of the zoonotic potential of this disease, which is historically difficult to treat in people and can be fatal. Nevertheless, treatments have been attempted with three to five medications, including ethambutol, given daily or twice daily for a year or longer, with documented recurrence after medication is stopped. Check with your local health department regarding the legal implications of treating an animal in your area.
FIGURE 15-25 Mycobacteriosis.
Amazon parrot with chronic nonhealing wounds on the leg caused by Mycobacterium kansasii. The parrot was euthanized after confirmatory diagnosis with a Fite’s modified acid-fast stain and polymerase chain reaction (PCR) performed at washington State Diagnostic Laboratory.
It is not common for birds to present with a bacterial dermatitis unless it is involving the plantar surface of the foot, as described under ulcerative pododermatitis, or there is underlying trauma that allowed the infection to start; if present, this generally involves gram-negative bacteria. A ferret developed suspected allergy and secondary Pseudomonas spp. dermatitis after the owner built it a cage made of redwood. After removal of the new homemade cage and appropriate antibiotic treatment, the ferret made a complete recovery.
Diagnosis usually involves aerobic and anaerobic culture and sensitivity, but may also include cytology, biopsy, or fungal culture. No allergy testing has been reported in ferrets. In this case, suspicion was high because the disease occurred after exposure to the new cage.
Clean and débride the wound; this is sometimes repeated over the course of days. Primary closure is performed once infection is controlled. Birds’ heterophils lack myeloperoxidase, an enzyme that liquefies pus; therefore do not place drains in the wound. Contaminated wounds are treated as in other animals. Antibiotic is based on culture.
FIGURE 15-26 Bacterial Dermatitis.
FIGURE 15-29 Bacterial Dermatitis.
FIGURE 15-30 Bacterial Dermatitis.
Young adult ferret with severe bacterial dermatitis due to Pseudomonas aeruginosa. The owner had recently hand-made an enclosure of redwood for the ferret, and although this was not proved, it was suspected that the ferret was allergic to the redwood. The ferret responded well to appropriate antibiotic therapy based on culture.
FIGURE 15-31 Bacterial Dermatitis.
FIGURE 15-32 Bacterial Dermatitis.
FIGURE 15-33 Bacterial Dermatitis.
Same gecko as in Figure 15-32 showing dysecdysis (abnormal shedding of the entire body). Retained sheds on toes have a constricted blood supply and cause necrosis of the toes. This gecko ended up responding to appropriate antibiotic therapy based on culture and multiple warm water soaks but lost almost all its toes.
Bacterial sepsis in reptiles can manifest as hyperemia of the ventrum in turtles or snakes, and as hyperemic conjunctiva in lizards. Historically, Pseudomonas and Aeromonas are the most common bacterial isolates from reptiles. Occasionally, boa-type snakes can also develop a cellulitis at the site of infection, which causes tremendous swelling. Snakes normally shed in one piece, whereas lizards shed in a piecemeal fashion from head to toe. Snakes will shed the spectacle over the eye first, turning the bluish color of the eye clear, which marks the beginning of a shed. Then, the snake sheds (ecdysis) the entire skin in one everted piece. Dysecdysis is an abnormal shed and is usually due to low humidity in the environment. During the week before and after a shed, a snake can mimic respiratory disease because of partial occlusion of the nares, and they may also develop a hyperemic ventrum.
Localized skin or shell infection on the ventrum can also present with hyperemia, but it is usually localized—not generalized. Days to weeks before a normal shed, a snake can mimic sepsis, showing a hyperemic ventrum and even increased respiratory sounds. A haziness to the skin and a “bluing” of the spectacle (scale over the eye) occurs just before a shed due to increase in lymph fluid under the spectacle. Inclusion body disease caused by a retrovirus-like agent can cause an abnormal shed, as well as neurologic signs. Sepsis can also cause a hyperemic ventrum. Respiratory disease can cause wet crackles.
Find the source of infection, obtain a culture or blood culture, and treat with appropriate antibiotics. Antibiotic treatment in reptiles is routinely given for 6 to 10 weeks. To encourage a shed, the reptile should be soaked in warm water. Never pull off the shed, especially the spectacle over the eye, as skin or corneal damage may occur. The old shed can be gently rubbed off in the water. Increase humidity in the habitat by adding a wide, shallow dish of water big enough for the reptile to soak on its own.
FIGURE 15-35 Sepsis.
FIGURE 15-37 Sepsis.