Exotic mammal geriatrics (Proceedings)

Taking care of the older exotic mammal

The average life span for the domestic ferret is six to eight years, the domestic rabbit seven to ten years, the guinea pig three to four years and for the rat two to three years. Veterinarians consider the ferret and rabbit to be middle-aged at three years and geriatric at five or more years of age, while a two year old rat is already entering its senior years. Ferrets as old as 10 years, rabbits as old as 13 years and guinea pigs as old as 6-7 years of age are occasionally seen.

With aging comes the need for more hands on care and observation. As in any geriatric species, the exotic mammal will spend a good amount of its time resting and sleeping. As a result, geriatric pet owners should be encouraged to take the time to observe their older pet and make note of changes in behavior, appetite or body functions. They should periodically run their hands over their pet to assure that they aren't missing subtle changes in muscle mass, and body weight and condition. Animals that lose control of urination or defecation need to be housed on substrate that allows urine to soak away from the body thus avoiding scald and perineal areas will need to be clipped/shaved periodically to discourage soiling. For those seniors with neurologic or orthopedic problems; rolled towels or stuffed animals can be placed around the pet to allow them to remain sternal and comfortable.

All exotic mammals should have a yearly physical examination. Starting at the age of three, annual blood work may help the veterinarian detect changes in function of the liver, pancreas, kidneys and other organs. After the age of five, a veterinary examination, including blood profile and urine exam, should be scheduled every 6 months along with annual radiographs to monitor changes in size and shape of the heart and other organs. The focus of the exams is to ensure the pet's health, develop a plan for preventing future health problems and follow up on any previous health issues

Preventative health care is important in keeping the older patient active and feeling good. Certain diseases are more common as the exotic mammal matures and being aware of the clinical signs associated with these diseases is a first step in early recognition. The list below identifies signs that may indicate a health problem in the aged exotic mammal patient.

     1. Decreased appetite

     2. Tiredness, decreased play activity

     3. Diarrhea or dark tarry stools

     4. Straining to urinate or defecate

     5. Vomiting

     6. Excessive urination

     7. Excessive drinking

     8. Weakness

     9. Dazed look or staring

     10. Drooling

     11. Pawing at mouth

     12. Grinding teeth

     13. Loss of fur

     14. Excessive itching

     15. Increased breathing rate or effort

     16. Weight loss

     17. Development of lumps or skin changes

     18. Seizures (medical emergency)

Nutrition

In general, geriatric diets are lacking for the exotic mammal and those available are based on diet modifications made for senior dogs and cats. Many senior diets advocate lower levels of protein, sodium, phosphorus to help diminish the side effects of nutritional intake on renal and cardiac health in particular. For herbivores senior diets are lacking and specific changes in nutritional needs have not been worked out. Using the aging horse as a model, geriatric pelleted diets for the herbivore may be available in the future.

Ferrets require a diet high in protein and fat. As a guideline, look for foods with no less than 20% fat and 30% protein. When checking the ingredient list, the first three contents listed should be animal proteins such as chicken, eggs or poultry by-products. The future of ferret nutrition will be towards even higher levels of protein as diets try to mimic what a non-domesticated ferret would eat in the wild. Some veterinarians and ferret owners advocate whole prey foods such as mice, rats or chicks, though the downside of these diets is owner inconvenience and the fact that many people find this distasteful. If the older ferret develops specific organ disease your veterinarian may recommend a special diet that is more appropriate for their health.

Modification of therapeutics

In small animal medicine drug dosages may be modified in the geriatric patient based on body and muscle condition scores as well as assessed renal and hepatic function. Although specific recommendations for geriatric exotic mammals are unavailable, drug dosage modification should be considered, especially when organ disease has been positively identified.

Euthanasia

Determining the appropriate time for euthanasia is difficult in many circumstances. The author usually discusses quality of life issues with pet owners and lays down some criteria for the client to look for in their aged pet. Lack of appetite, inability to move well, and a lack of response to owner interaction may all be used. When it is time for euthanasia many owners want to be present. The author prefers to administer injectable anesthetics such as a combination of dexmedetomidine (0.1-0.2mg/kg IM) and butorphanol (0.2-0.5mg/kg IM) and encourages owners to hold their pets until sedated. Inhalant gas anesthesia is added as needed and euthanasia solution administered intravenously.

The ferret

Some common medical conditions seen with increased frequency in the geriatric pet ferret:

Adrenal disease

Adrenal-associated endocrinopathy (hyperadrenocorticism) in ferrets is a well-known, frequently occurring disease in ferrets. It can be caused either by adrenal hyperplasia or neoplasia (most commonly cortical adenoma or adenocarcinoma). In many cases the enlarged adrenal gland shows a mixed histological picture with adenocarcinoma cells being in the majority as the disease progresses. Metastasis is very uncommon and most adrenal neoplasms tend to be locally invasive rather than metastatic.

The diagnosis of adrenal disease in ferrets is frequently straightforward and can often be made on history and clinical signs alone. A skilled practitioner may be able to palpate an enlarged adrenal gland. Ultrasonography may identify an enlarged gland and offers the benefit of determining if right, left or both adrenals are affected.(1) Unlike canine Cushings disease evaluations of cortisol levels are not helpful. In the ferret hyperadrenocorticism primarily results in elevations in sex steroids.(2) The University of Tennessee provides an assay that measures plasma concentrations of androstenedione, 17 α-hydroxyprogesterone and estradiol. In approximately 85% of ferrets with hyperadrenocorticism there is unilateral adrenal enlargement, while in the other 15% of cases bilateral enlargement is seen. Clinical manifestation of signs may vary depending on which sex steroid is more elevated, and clinical signs may not correlate with degree of adrenal gland neoplasia or level of hormone elevation. Seasonal alopecia in many ferrets may be a normal physiological occurrence and should not be confused with adrenal disease.

Treatment options:

Surgery

May result in definitive treatment for adrenal disease in ferrets if the affected adrenal tissue can be remove in its entirety

Medical

Leuprolide acetate (Lupron- TAP Pharmaceuticals) is a long-acting gonadotropin-releasing hormone analog that inhibits the release of LH and FSH from the pituitary. Deslorelin acetate (Suprelorin, Peptech Animal Health) is a slow release GnRH implant that is not approved for use in the United States.

Insulinoma

Insulin-secreting pancreatic islet cell tumors are among the most common neoplastic diseases affecting ferrets. Synonyms include functional islet cell tumor, pancreatic B-cell tumor, pancreatic endocrine tumor and insulinoma. The disease affects both male and female ferrets between the ages of 2 and 8 years, but is most commonly diagnosed in ferrets 4 to 5 years of age. On histopathologic examination beta cell carcinoma is most often found, sometimes in combination with beta cell adenoma or hyperplasia. Metastasis is uncommon; however, when it does occur it is usually to the regional lymph nodes, spleen or liver.

The serum glucose concentration required for diagnosis of hypoglycemia in the ferret is a matter of some debate. However, most clinicians agree that a 4-hour fasting glucose concentration of less than 60mg/dl is very suggestive of insulinoma.(3) The reference range for normal fasting blood glucose concentrations in ferrets is 90 to 125 mg/dl.(4)

Long term treatment options include dietary, medical and/or surgical management, and many ferrets require a combination of all three to successfully control the clinical signs of hypoglycemia associated with insulinoma. The choice of therapy depends on severity of clinical signs, the age of the ferret, concurrent disease, and the owner preference.

Malignant lymphoma is a common diagnosis in pet ferrets. In a retrospective study of 574 ferrets with neoplastic disease, Li, et al found that 15.2% were hemolymphatic in origin and of these 78% were malignant lymphomas.(5) Clinical signs of malignant lymphoma vary with the location of the disease as well as the age of the animal. Lymphoma can affect numerous tissues with the visceral and peripheral lymph nodes, spleen, liver, mediastinum, bone marrow, lung, intestine, and kidney being most commonly affected. Less frequently involved are the stomach, pancreas, nervous system and orbit. Diagnosis of lymphoma involves biopsy of affected lymph nodes or visceral organs with direct visualization of neoplastic cells and evaluation of cellular morphology. The large fat pads surrounding ferret peripheral lymph nodes make obtaining an adequate sample via fine needle aspiration difficult. Treatment choices for ferret lymphoma include surgery, chemotherapy, radiation, alternative therapy or combination therapy involving these modalities.

The rabbit

Some common medical conditions seen with increased frequency in aged pet rabbit:

Perineal soiling and dermatitis

Rabbits often present with matted and soiled perineal fur with secondary dermatitis. Causes include inappropriate diet and subsequent soft stools or diarrhea, urine leakage as the result of infection or excessive crystaluria (bladder sludge syndrome), environmental factors resulting in behavioral urine retention, and decreased ability to groom due to obesity or pain.

Rabbit neurological disease

Signs of neurologic disease in rabbits include behavioral changes, head tilt (labyrinthine torticollis or wry neck), nystagmus, tremors, paresis, paralysis, and seizures. Head tilt, usually an indication of vestibular dysfunction, can be central (cerebellum, brain stem) or peripheral (inner ear), and was the most common clinical sign noted in a retrospective study of rabbits with neurologic disease. (6) Ataxia, paresis, and paralysis can also be caused by central (brain or spinal cord) or peripheral nerve disease.

Head tilt

Head tilt, which is usually an indication of vestibular dysfunction, can be central (cerebellum, brain stem) or peripheral (inner ear), and was the most common clinical sign noted in a retrospective study of rabbits with neurologic disease.(6) Other vestibular signs include nystagmus and loss of balance and rolling. Causes include bacterial otitis interna and infection with Encephalitozoon cuniculi

Spondylosis and osteoarthritis

Age-related osteoarthritis (degenerative joint disease) and spondylosis (degenerative spinal defects) are now more commonly encountered as improved husbandry and nutrition have extended the lives of pet rabbits. Owners of affected rabbits typically report an abnormal gait, lameness or inability to hop. The signs of musculoskeletal pain may be more subtle with the quiet and immobile nature of affected rabbits being attributed to age. Still other rabbits demonstrate lack of proper grooming due to a reluctance or inability to reach the caudal body and perineum resulting in an unkempt coat and/or perineal soiling and dermatitis. Radiographs of joints with degenerative disease may show capsular distension, osteophytosis, narrowing joint spaces or surrounding soft tissue thickening or mineralization. Spondylosis is identified radiographically by spinal exostoses, degenerative changes and spinal defects such as kyphosis, lordosis or scoliosis.

Abduction or splaying of the front limbs may also be seen in sedentary senior rabbits. This may occur as the result of inactivity and resulting muscle wasting so that over time the front limbs are not adducted under the body and splay out. Obesity and osteoarthritis probably contribute to this condition and once started is hard to reverse. Prevention or diminishing progression involves trying to improve muscle tone through increased activity, housing on a surface that allows for firm footing and treating any underlying predisposing conditions.

The guinea pig

Some medical conditions seen with increased frequency in the aged guinea pig:

Hyperthyroidism

Hyperthyroidism is the result of an overactive thyroid gland that is producing excessive hormone which increases the metabolic rate and calorie burning in the affected animal's body. Affected pigs show an increased appetite, many times a voracious one, and a concurrent weight loss in spite of increased food intake.(7) Other signs noted in hyperthyroid pigs include hyperactivity, increased thirst and urination, soft stools and a rapid heart rate. Treatment involves daily oral anti-thyroid medication or radioactive treatment with I-131, both similar options used in cats with the same disease. (7)

Mammary gland tumors in guinea pigs

A retrospective study of pigs with mammary tumors found that males and females were equally represented, but that those tumors found in males were more likely to be malignant vs. benign. (8) Benign hyperplasia was the more likely diagnosis in those female pigs with mammary gland enlargement. (8)

No data was available on chemotherapy for those malignant tumors. Future research will look for estrogen receptors on these mammary tumors to see if a chemotherapy drug such as Tamoxifen (Nolvadex®), a drug that interferes with the activity of estrogen, may work.

Ovarian cysts

In clinical practice, cystic ovarian disease is commonly diagnosed in guinea pigs. Bilaterally symmetrical alopecia and clinical signs secondary to a space-occupying abdominal mass are most commonly observed. Although this study provided useful data on the prevalence and size of cysts in sows of different ages, data correlating clinical signs and presence of ovarian cysts would have been valuable for the veterinary practitioner. According to previous studies, ovarian cysts typically arise from the rete ovarii and are not typically hormonally active. Another study observed a 22.4% prevalence of follicular cysts in normal cycling sows. (9) Perhaps there may be a correlation between clinical signs such as alopecia and the presence of follicular cysts. Ultrasonography cannot definitively distinguish a follicular cyst from a rete ovarian cyst. Treatment options include surgical ovariohysterectomy or medical therapy (GnRH [Cystorelin® Merial) 50 ug/ml] - 25 ug/pig q2wk for 2 injections) (10)

Rodents

The following outlines some medical conditions seen in the pet rodent with increased frequency as they age.

Rodent respiratory disease complex

Rodent Respiratory Disease Complex is seen commonly in rats, hamsters and guinea pigs. Affected rodents show signs of repeated sneezing, nasal discharge, brown to red eye discharge and diminished appetite. Affected rodents may also make a "chattering' noise because of nasal congestion. Sometimes the infection goes to the inner ear, affecting the balance center and resulting in a head tilt. Rodent respiratory disease is called a "complex" because it may be caused by a variety of infectious agents with environmental and nutritional issues also playing a role. To confuse matters more, many of the infectious organisms involved in Rodent Respiratory Disease Complex can be subclinical. When a new carrier or subclinical pet is introduced to a household with preexisting pet rodents the carrier may shed infectious agents and spread disease among susceptible members of the pet colony. Subclinical cases can also become clinical as a result of secondary environmental stresses particularly poor cage design/ventilation and an inadequate diet. Treatment of Rodent Respiratory Disease Complex includes antibiotic therapy and improving diet and cage care. In spite of the best care and nutrition it is not uncommon for this disease to recur. It is a common disease entity in the geriatric rat and in spite of varying treatment regimens, including varying systemic antibiotics, (enrofloxacin, 10mg/kg PO q12h, doxycycline, 5mg/kg PO q12h, or azithromycin (20mg/kg q24h, 7 days.) (11)

Rat mammary tumors

Anatomically, the mammary gland tissue in the rat extends on either side of the ventral midline from the axillary to the inguinal regions, and mammary gland tumors may occur anywhere in this area.(12)) Mammary gland neoplasms are probably the most common spontaneous tumors found in the rat. Adenomas and cystadenomas are uncommon, and carcinomas of varying types (adenocarcinomas, papillary carcinoma, comedocarcinomas, and squamous cell carcinoma) are said to comprise less than 10% of all spontaneous mammary gland tumors in the rat.(13) Mammary fibroadenoma represents approximately 85-90% of all mammary tumors in the rat. These neoplasms are most common in older rats, though may also occur in young females and males. Overall, the biological behavior is benign; the neoplasms can become very large, ulcerate, and infiltrate locally, but they rarely metastasize.

References

Besso JG, Tidwell AS, et al. Retrospective review of the ultrasonographic features of adrenal lesions in 21 ferrets. Vet Radiol Ultrasound; 41(4): 345-352, 2000

Johnson-Delaney CA. Update of Ferret Adrenal Disease: Etiology, Diagnosis and Treatment, Proceedings of the Association of Avian Veterinarians, Monterrey, 2006; 69-74

Fox JG, Marini RP. Diseases of the Endocrine System. In: Biology and Diseases of the Ferret, 2nd ed, Fox JG (ed.). Baltimore: Williams & Wilkins, 1998; 405-447.

Quesenberry KE, Rosenthal KL. Endocrine Diseases, In: Ferret, Rabbits and Rodents 2nd ed, Quesenberry KE, Carpenter JW (eds.), Elsevier, Philadelphia, 2004 79-90

Li X, Fox JG, Padrid PA. Neoplastic Diseases in Ferrets: 574 cases (1968-1997). JAVMA: 212(9) 1402-1406, 1998

Gruber A, Pakozdy A, Weissenböck H, et al. A retrospective study of neurological disease in 118 rabbits. J Comp Pathol 2009; 140:31-37.

Mayer J, Wagner R. Clinical Aspects of Hyperthyroidism in the Guinea Pig. Proceedings of the Association of Exotic Mammal Veterinarians, Milwaukee, 2009: 69-73.

Gibbons, P, Garner M. Mammary Gland Tumors in Guinea Pigs (Cavia porcellus), Proceedings of the Association of Exotic Mammal Veterinarians, Milwaukee, 2009:83.

Shi F, Petroff BK, Herath CB, et al. J Serous cysts are a benign component of the cyclic ovary in the guinea pig with an incidence dependent upon inhibin bioactivity Vet Med Sci; 64(2):129-35, 2002

Mayer J. The Use of GnRH to Treat Cystic Ovaries in a Guinea Pig. Exotic DVM: 5(5); 36, 2003

Tamura Y. Current Approach to Rodents as Patients, Journal of Exotic Pet Medicine, Standards of Care. Amy Worrell (ed; 19(1): 36-55, 2010

Altman NH, Goodman DG: Neoplastic diseases, In Baker HJ, Lindsey JR, Weisbroth SH (eds.): The Laboratory Rat, vol 1, Biology and Diseases, Orlando, FL, Academic, 333-337. 1979

Toft JD: Commonly observed spontaneous neoplasms in rabbits, rats, guinea pigs, hamsters and gerbils, In Fudge AM, Schmidt RE (eds.): Seminars in Avian and Exotic Pet Medicine; 1(2): 80-92, 1992