Ferret Medicine

Introduction

In exotic animal practice, the ferret is the closest of the commonly seen species to the traditional canine and feline pets. Principles of diagnosis and treatment used for these species can be used for ferrets with good success. Ferrets make ideal patients as they are docile, hardy, and quiet pets. They require little space in the hospital, adapt readily, and tolerate medical procedures well. There are some differences in behavior, techniques and disease susceptibility that the clinician should know, however, so that a diagnosis and treatment can be achieved more easily and efficiently. These differences will be emphasized here.

Ferret Husbandry

Ferret requirements are not difficult to meet. Like any other animal, however, serious problems can result from failure to meet these requirements.

Housing

Most households are not suitable for ferrets to be allowed to roam unsupervised. These mischievous creatures can get into the smallest crevices and will often get themselves into dangerous situations. Foreign object ingestion is common and ferret environments should be ferret-proofed to prevent foreign body ingestion. Large wire cages are usually considered best for ferrets. Aquaria tend to have poor ventilation, thereby causing stress to the animal. Multilevel cages with ramps and fences allow more exercise within the cage confines. Toys should be chosen for safety. Many ferrets have a taste for rubber so toys made of this material should be avoided. Ferrets often choose a corner of the cage for eliminating wastes. If a litter box is placed in this area it will facilitate cleaning. Cellulose litters are preferred over clay cat litter as clay litters are usually dusty and can contribute to respiratory problems.

Nutrition

Ferret nutrition research is not as extensive as canine and feline nutrition research. As carnivores, the natural diet of ferrets is small creatures, usually rodents. In captivity, however, they are usually fed specifically formulated ferret diets. Only very high quality feline diets are acceptable and the highest protein and fat should be chosen. Young ferrets probably require about 38% protein and 20% fat. Slightly lower amounts may be acceptable for mature ferrets. During winter months, fatty acid supplements may be required to keep a healthy coat. All ferret diets should be meat based. Attempts at using plant based diets always result in health problems in ferrets. Carbohydrates and fiber are not handled well by ferrets so diets low in these should be selected. Treats should be limited.

Handling

Most ferrets are docile, friendly, curious creatures that are easily handled without restraint. The stories accounting their foul nature and tendencies to bite are mostly propaganda generated by those who wish ferrets to be banned. Young ferrets can be “mouthy” and caution should be taken, but severe bites are uncommon. Docile ferrets can be lifted under the chest and held on the forearm. It is somewhat difficult for them to hold still, however, so further restraint may be necessary during the veterinary exam. When ferrets are dangled by the scruff of the neck with the feet off of the table, they relax, often yawn, and stop struggling (Figure 1).

Reproduction

This is not an issue with the majority of ferrets seen in practices in the United States. Marshal Farms produces most of the ferrets sold in pet stores and their policy is to spay or neuter the babies prior to sale. Therefore it is extremely uncommon to find reproductively intact ferrets. While early neutering has made ferrets more sellable and perhaps has made regulatory agencies see ferrets as less risky, some health problems may be associated with this practice.

Female ferrets are known as jills and are seasonal induced ovulators. They will remain in heat for extended periods of time if not bred. This can lead to severe problems as will be discussed later. Litters of 5–10 kits are produced after a gestation of 42 days. Kits open their eyes at 25–35 days and are weaned at 6 weeks.

Male ferrets are called hobs. Intact males possess a strong musky odor and have a tendency to spray their anal sac contents for marking or defense. Their prepuce terminates on the ventral abdomen much like in a dog, making even very young ferrets easy to sex. Neutering male ferrets will reduce their musk and the tendencies to spray. Descenting makes little or no difference in the odor.

Preventive Health Care

Preventive health care is very similar to that in dogs and cats. Early detection and treatment of disease, vaccinations, parasite control, neutering, and dental prophylaxis are all used to maintain their health. For this reason, ferrets are easily incorporated into small animal practices. The veterinarian should become familiar with ferret behavior, anatomy, and diseases but little special equipment is required.

Vaccinations

Ferrets are highly susceptible to canine distemper virus. Use of a FDA approved MLV chick embryo vaccination (Fervac) is currently available as well as a recombinant vaccine (Purevax Ferret Distemper). The initial series is given every 3-4 weeks until 14-16 weeks of age. Label recommendations advise annual boosters although duration of immunity studies are lacking  and viral neutralizing antibodies likely last well over 3 years and possibly as long as 7 years, so triannual after the initial 1 year booster may be sufficient for low risk ferrets. Vaccine adverse reactions can be minimized by thoroughly warming and mixing the contents of the vials for 5 minutes. Some practices will no longer administer two vaccinations on the same day to a ferret. This recombinant vaccine does NOT contain the whole distemper virus, thus eliminating the risk of viral shedding, post-vaccinal encephalitis, and possible reversion to virulence which have been associated with MLV distemper vaccines used for ferrets previously. Ferrets are not susceptible to feline distemper and should not be vaccinated for this. Ferrets are somewhat susceptible to Bordetella so it may be advisable to vaccinate them for this disease in high risk situations (shows, etc.).

Rabies

Rabies vaccination is more for legal protection than for protection from the rabies virus. Most pet ferrets have literally no potential exposure to rabies. However, if a ferret bites someone, even accidentally, the legal position of many regulatory agencies is to euthanize the ferret and test for rabies. Since the approval of Imrab-3 (Merial) for ferrets, some agencies will allow vaccinated ferrets to be quarantined like dogs or cats. Vaccinating with unapproved products is not justified. Although this product can be given every three years in dogs or cats, it is only approved for one year in ferrets.

Neutering and descenting

Neutering ferrets can prevent all of the problems associated with the reproductive tract. In jills, it is essential unless they can be bred at each heat. In the United States, most young ferrets are purchased already neutered. Ideally, ferrets should be neutered later at 4 to 6 months of age. While most ferrets have also been descented at the time of adoption, this provides no health benefit and is of very questionable value.

Heartworm prevention

Heartworm prevention is important in endemic areas. Like cats, ferrets have a lower susceptibility to heartworm but a single worm can cause severe disease. Diagnosis and treatment are difficult and prevention is easy. Advantage Multi is the only approved monthly topical heartworm preventive for ferrets. It is also labeled for flea and earmite treatment and prevention.

Geriatric monitoring

Geriatric monitoring is an extremely important part of ferret health care. Several conditions are extremely common in ferrets over 3 years of age and early detection is important if successful therapy is to occur. The frequency of examination should increase to every 6 months after 3 years of age and at least one of these should be accompanied by laboratory and other diagnostics. Minimally, a complete blood count and a fasting blood glucose should be performed. Preferably a full chemistry profile, radiography, or ultrasound evaluation should be done.

Dental prophylaxis

Dental prophylaxis is important in ferrets. As a ferret ages periodontal disease can progress to serious stages with pain, tooth loss, and gingivitis. Unfortunately many ferrets do not live long enough for this to become a problem due to other problems but dental care must be included if good long term health is to be achieved.

Diagnostic Approach

Ferrets make ideal patients. They are hardy, resilient, easily handled, and most clinical procedures can be easily mastered. They are carnivores like dogs and cats, with similar anatomy and physiology.

A thorough history should be taken on ferrets, including age, previous medical problems, if and when they were neutered, husbandry, vaccinations, and the problem at hand. The history can often give a strong indication of what the problem may be but it is important that the clinician does not develop tunnel vision toward that problem. Concurrent diseases are quite common; a systematic approach is critical.

Examination of ferrets should be done systematically and include a visual inspection of the eyes, nose, ears, skin, coat, and the genital and anal openings; palpation of the lymph nodes, thorax, abdomen, and limbs; and auscultation of the thorax. The oral cavity and teeth should be examined carefully. It is very common for one or more of the canine teeth to be broken. Abdominal palpation should take place with the ferret held vertically by the scruff. This allows the viscera to “fall” caudally so they are more easily palpated. Splenomegaly is very common in ferrets and may or may not be significant. Normal ferrets are very relaxed during palpation; a tense abdomen may indicate pain. Very little gas is generally present in the intestinal tract of ferrets. Extensive gurgling or borborygmus should be considered significant.

Normal values (as stated)

• Body temperature: 101 to 103°F
• Heart rate: 180–250 beats per minute
• Respirations: 10 to 40 per minute

Radiography and ultrasound

Radiography is often part of the workup in ferrets. It is especially valuable for detection and evaluation of gastrointestinal, respiratory, and cardiac diseases. There is a large amount of intraperitoneal fat in most ferrets, giving substantial contrast. Splenomegaly is a common but fairly non-specific finding. Very little gas is normally present in the gastrointestinal tract. The intestinal loops should be no larger than 2–3 times the diameter of the ribs; larger loops may suggest an obstruction. The heart of ferrets is conical shaped, more like that of a cat than a dog. The hook shaped os penis is easily visible radiographically. Imaging using other techniques such as ultrasound is receiving more attention; ultrasound can evaluate the heart, liver, spleen, bladder, and, most significantly, the adrenals and pancreas.

Blood testing

Blood testing in ferrets follows the same principles as in dogs and cats. An adequate sample can be drawn for most tests needed. Blood can be drawn from the jugular vein, the cranial vena cava, the cephalic vein, the lateral saphenous vein, or the ventral caudal artery/vein. Because of the small size, the larger vessels yield a good sample more readily than the peripheral vessels.

Hematology should be part of the workup for any sick ferret and part of the geriatric workup of ferrets over 3 years. Normal ferrets have a relatively high hematocrit, which leads to low plasma/serum yields. The normal white blood cell count of ferrets is quite low compared to canine and feline patients and elevations in the white blood cell count are uncommon. The complete blood count should be interpreted similarly to dogs and cats. Lymphocytosis is sometimes seen in ferrets with lymphoma. Eosinophilia will be seen in ferrets with eosinophilic gastroenteritis.

Chemistries are also valuable in the evaluation of ferrets. Interpretation follows the same principles as in more familiar pets. One exception noted is that creatinine may not be reliable for indicating renal failure.

Endocrinology

Endocrinology is a valuable diagnostic aid in ferrets due to the high incidence of endocrine disorders. Common endocrine tests used in dogs and cats are of little value in ferrets. Testing thyroid function is generally not indicated. While adrenal disease is quite common, standard adrenal function testing is not applicable, since the diseased adrenal of ferrets secretes estrogen and other sex steroids rather than cortisol or corticosterone. The most common endocrine disorders noted are insulinoma and adrenal-associated endocrinopathy. Measuring insulin levels (especially with glucose levels) is useful for diagnosis of insulinomas. For detection of adrenal endocrine diseases, estradiol, androstenedione, dehydroepiandrosterone, and 17-hydroxyprogesterone should be measured; values should be compared to reference ranges for the laboratory used.

Exploratory surgery

Exploratory surgery is a commonly used diagnostic tool in ferrets. Because of the high incidence of abdominal disease, it frequently yields a definitive diagnosis for many common conditions. Regardless of the suspected condition, a complete exploration of the abdomen is indicated. Biopsies should be taken if any suspicious lesions exist. When intestinal obstruction is even vaguely suspected, an exploratory should be performed as soon as possible.

Soft Tissue Surgery

Ferrets make ideal surgical patients. They are easily anesthetized using isoflurane, easily intubated, intravenous catheters are easily placed, they have shallow body cavities allowing excellent visualization, and they are exceptionally resilient to surgical manipulation.

Ovariohysterectomy and castration were once the most common procedures, but are now rare since most pet ferrets are purchased already neutered. If needed, the procedure is described as identical to that of a cat.

Adrenal surgery (as described)

Excision of diseased adrenal glands is described as a common surgical procedure. However now with GnRH hormone therapy (implants or injections), surgery may not be needed. The left adrenal lies just cranial to the left kidney in retroperitoneal fat; when normal, it may be barely visible as a small nodule. The left adrenal is crossed by the adrenal lumbar vein and lies near the aorta; the vessel must be ligated or clipped or electrocoagulated before dissection. The right adrenal lies slightly more cranial, dorsal to the caudate lobe of the liver, and is adherent to the caudal vena cava, making surgery more difficult and higher risk. Occasionally both adrenals are affected; in such cases the entire left gland is removed and a portion of the right is resected.

Gastrointestinal surgery

Gastrotomy and enterotomy procedures are common due to foreign body ingestion and obstructive hairballs. The procedure is described as the same as in dogs and cats, using smaller sutures.

Urogenital surgery

Urinary obstruction may occasionally occur in male ferrets; if medical therapies fail or obstruction recurs, a urethrostomy may be required.

Diseases of Ferrets

Ferrets are host to a wide variety of conditions. Some are treated the same as in dogs and cats; others are more common, differ in nature, or are treated differently.

Insulinoma

Insulinoma is described as uncommon in dogs but very common in ferrets. These are beta cell tumors of the pancreas that secrete excessive insulin, causing hypoglycemic episodes. Signs may include weakness, lethargy, salivation, pawing at the mouth, or seizures. The tumors are described as generally malignant and can metastasize to the liver, spleen, or other tissues. Presumptive diagnosis is based on low fasting blood glucose (<70 mg/dl) after a 4–6 hour fast (longer fasts could precipitate dangerous hypoglycemia). Insulin levels may be measured; definitive diagnosis is based on histopathology from exploratory laparotomy.

Treatment may be medical or surgical. For seizures or comatose episodes, an IV catheter and slow administration of 50% dextrose to effect is described, followed by oral feeding once conscious. Surgical debulking can slow progression but is rarely curative due to multiple nodules. Dietary management includes frequent feedings of a high protein, high fat diet. High sugar material may be used during episodes only when necessary; Nutrical is noted as useful. Chromium supplementation (including brewers yeast) is discussed as being a helpful supplement in regulating blood glucose levels. Prednisolone may be used to promote gluconeogenesis and inhibit glucose uptake; diazoxide may be used to inhibit insulin release and reduce cellular uptake of glucose. While this disease is rarely cured, many ferrets can be controlled and live months to years after diagnosis.

Adrenal endocrinopathy

Adrenal endocrinopathy is described as uncommon in dogs and cats but extremely common in ferrets, representing a continuum of adrenal hyperplasia, adenomas, and adenocarcinomas. It usually occurs in ferrets over 3 years of age; left adrenals are more commonly affected than right, and both may be affected rarely. Estrogen and its precursors are secreted rather than cortisol/corticosterone, and affected ferrets should not be referred to as Cushingoid. Bilaterally symmetrical alopecia is described as the hallmark; vulvar enlargement may be seen in females; males may show aggression or sexual behavior, and prostatic cysts may occur. Some reduction in muscle tone and lethargy may be present; in severe cases, estrogen-induced bone marrow suppression can occur.

Diagnosis can be supported by endocrine testing of sex steroids (estradiol, androstenedione, dehydroepiandrosterone, and 17-hydroxyprogesterone), not cortisol. ACTH and dexamethasone suppression tests are of no diagnostic value in ferrets. Ultrasound may aid detection and determine affected side and presence of metastases or concurrent disease. Exploratory laparotomy and visual inspection can diagnose; removal of the affected gland is described as the treatment of choice, with histopathology after removal. Prednisolone is noted as reducing post-operative depression. Surgery can be performed however GnRH agonist hormone therapy (Lupron (leuprolide acetate) a monthly injection and SUPRELORIN® F (deslorelin acetate) a 12 month implant) can assist in the management and even prevention of adrenal disease in ferrets.

Estrogen toxicosis

Once common, this disease is described as rarely encountered today. Jills may remain in heat until bred; extended estrus can lead to bone marrow suppression and pancytopenia. Affected jills may be weak, pale, sometimes shocky, with a swollen vulva. Diagnosis is based on history and CBC findings (anemia, leukopenia, thrombocytopenia). Treatment includes ovariohysterectomy for mild cases; for breeding or poor surgical candidates, human chorionic gonadotropin (100 IU once, repeat in 2 weeks if needed) may be used to stimulate ovulation. Transfusions may be needed, and all ferrets have the same blood type.

Lymphoma/lymphosarcoma

Lymphoma is described as a common neoplastic disease of ferrets affecting various ages, with unknown etiology. Clinical features are described as similar to dogs. Lymphadenopathy is the hallmark; peripheral, mediastinal, sublumbar, or mesenteric nodes may be involved. Peripheral lymphocytosis may be seen. Splenomegaly often occurs. Weight loss progresses; GI or respiratory signs may occur as nodes enlarge. Diagnosis is made by cytology or histopathology of lymph node aspirates/biopsies or spleen/other lymphatic tissues. Chemotherapy protocols include vincristine, cyclophosphamide, prednisolone, and/or doxorubicin. Prognosis is guarded; remissions of months to years are reported, and best candidates are described by disease localization and bone marrow status.

Aleutian disease

Aleutian disease is described as a disease of mink that ferrets are also susceptible to. It is caused by a parvovirus but is characterized as an immune complex disease. Clinical signs include weight loss, hepatomegaly, and neurologic signs. Hypergammaglobulinemia, glomerulonephritis (proteinuria, casts, azotemia), and plasmacytosis may be found. Diagnosis is based on hypergammaglobulinemia and a positive titer. There is no cure, vaccine, or specific antiviral treatment for Aleutian Disease Virus (ADV) in ferrets. Treatment focuses on managing symptoms, reducing immune-mediated damage, and providing supportive care to prolong life.

Canine distemper

Ferrets are described as very susceptible to canine distemper, though vaccination has made it relatively rare. Signs include high fever, mucopurulent oculonasal discharge, pedal hyperkeratosis, inguinal dermatitis, and neurologic signs. In ferrets, it is described as 100% fatal. Prevention is vaccination at 2–3 week intervals until 14 weeks old.

Gastric/intestinal obstruction

Hairballs or foreign bodies causing partial or complete obstruction of the stomach or small intestine are described as very common. The small intestinal lumen will not allow passage of even very small objects. Ferrets often ingest harmful items, especially rubber and foam rubber products. Foreign bodies are more common in younger ferrets. Gastric obstruction may present as chronic weight loss and lack of appetite with or without vomiting (vomiting is described as uncommon). Intestinal obstruction presents acutely with anorexia, dehydration, abdominal pain, and severe depression. Diagnosis is based on palpation or radiography; contrast studies are discussed as potentially inconclusive. Confirmation is by exploratory laparotomy. Treatment is gastrotomy or enterotomy; for intestinal obstruction, surgery should be performed as soon as possible (within hours), along with supportive care.

Proliferative bowel disease

Proliferative bowel disease is described as caused by an organism now called   Lawsonia intracellularis. Chronic diarrhea is the primary sign; partial rectal prolapse may be seen; weight loss can be dramatic due to malabsorption. Young ferrets are most commonly affected. Culture is difficult; diagnosis is challenging and presumptive diagnosis is based on signalment and signs. Fecal cytology may reveal spiral/curved bacteria but is not definitive because   Helicobacter  appears similar. Chloramphenicol (50 mg/kg BID) is listed as treatment of choice, with fluids and nutritional support. Treating concurrently for helicobacter gastritis may be advisable in severe cases.

Helicobacter gastritis

Helicobacter mustelae  is described as a spiral-shaped bacterium that can cause gastritis and gastric ulceration in ferrets and is studied as a model for human ulceration. Stress-associated onset is noted. Signs may include vomiting, anorexia, weight loss, diarrhea, and melena. Presumptive diagnosis can be made from signs; hematology may show anemia or occasional toxic leukocyte changes. Definitive diagnosis is by surgical or endoscopic examination and gastric biopsies. Treatment includes amoxicillin (20 mg/kg BID) with or without clavulanic acid, metronidazole (20 mg/kg BID), and GI protectants such as bismuth subsalicylate (1 cc/kg BID), H2 blockers (cimetidine 10 mg/kg TID), or sucralfate (25 mg/kg BID), plus supportive care.

Eosinophilic gastroenteritis

This disease is described as uncommon most often in mature to older ferrets. Etiology is unknown and suspected to be a hypersensitivity reaction. Clinical signs include diarrhea, anorexia, vomiting, and weight loss. Peripheral eosinophilia is described as present in most cases. Treatment includes prednisolone at 2 mg/kg SID for a week and then every other day until resolved, with tapering. Supportive care is provided as needed.

Epizootic catarrhal enteritis

This is described as a major gastrointestinal disease of ferrets of unknown viral etiology, however a coronavirus is suspected. It affects ferrets of any age, often with recent exposure to other ferrets (shows, fairs, shelters). The primary sign is green, mucoid diarrhea (“Green Slime Disease”). Diagnosis is based on history and clinical signs; treatment is supportive care and treating differentials that have not been ruled out. Morbidity is high but mortality is low; most recover in two to four weeks.

Cardiomyopathy

Ferrets may develop dilated or hypertrophic cardiomyopathy and valvular disorders such as mitral insufficiency. Dilated cardiomyopathy consists of using taurine deficiency has been speculated but not supported. These disorders may lead to congestive heart failure (CHF). Diagnosis relies on physical exam, radiographs, ECG, and echocardiogram. Findings include lethargy, weight loss, anorexia, respiratory distress, hypothermia, tachycardia, systolic murmur, moist rales, muffled heart and lung sounds, ascites, and rear leg weakness; muffled heart sounds are described as more common than murmurs. Treatment of CHF is described as furosemide 2–4 mg/kg BID, digoxin 0.01–0.02 mg/kg SID, enalapril 0.5 mg/kg every 24 to 48 hours and after 48 hours pimobendan 0.5mg/kg PO every 12 hours. Many ferrets are in advanced stages at diagnosis and live less than one year.

Splenomegaly

Splenomegaly is described as very common and fairly non-specific. It is important to interpret splenomegaly in context and not assume the spleen is the primary problem until other problems are ruled out. Diseases of concern include lymphoma and metastatic neoplasia. Needle aspirate can help define the problem at the cellular level. If the spleen is irregularly shaped or physically interfering with anything else, it most likely is diseased and removal may be necessary.

Influenza

Ferrets are described as susceptible to human influenza viruses. Mild to moderate upper respiratory signs are noted. Generally the disease is self-limiting and treated symptomatically. Diphenhydramine can be helpful at 1–2 mg/kg BID, with fluids and nutritional support as needed.