Ferret_evaluating And Stabilizing The Critical Ferret

V CE

Vol. 22, No. 3 March 2000

Refereed Peer Review

FOCAL POINT ★ Ferrets are subject to several diseases that require prompt recognition and specific diagnostic steps to ensure adequate critical care.

Evaluating and Stabilizing the Critical Ferret:

Initial Assessment, Differential Diagnosis, and Diagnostic Plan

KEY FACTS ■ Ferret physiology, as well as response to medical therapy, is similar to that of domesticated cats and dogs. ■ Because spinal injury is rare in ferrets, hindlimb paresis is typically a sign of weakness and not intervertebral disk disease. ■ Young ferrets are notorious for ingesting foreign matter, particularly rubber items. ■ Urinary obstruction in male ferrets has been associated with prostatomegaly and hyperandrogenism. ■ The effects of isoflurane gas on ferret hematology is profound and can have consequences for blood transfusion and interpretation of diagnostic samples.

University of California

Indianapolis Zoo, Indianapolis, Indiana

Keith G. Benson, DVM

Jan C. Ramer, DVM

University of Wisconsin

Joanne Paul-Murphy, DVM ABSTRACT: Because of their small size and unique diseases, critically ill ferrets can be a diagnostic and treatment challenge for clinicians. Ferrets are often in advanced stages of a disease process at the time of presentation, necessitating aggressive supportive care. History and clinical signs can be vague; thus the differential diagnosis list may include many disorders, such as metabolic disease, toxicity, cardiac disease, neurologic disease, and neoplasia.

T

o appropriately render emergency care to critically ill ferrets, clinicians must use their familiarity with common diseases of ferrets and knowledge of principles of basic small animal critical care. The initial diagnostic plan depends on the history and clinical signs (Table I). The results of diagnostic tests aid clinicians in diagnosing the disorder and developing a treatment plan (Table II1–5). This article focuses on common presenting signs, associated differentials, and initial diagnostic and therapeutic plans that are specific to ferrets. Dyspnea, gastrointestinal disorders, urethral obstruction, anemia, and cardiac and endocrine disorders are discussed.

DYSPNEA As with any dyspneic patient, supportive care may supersede the acquisition of diagnostic samples. Oxygen therapy is advised before, during, and after any stressful procedure. The initial diagnostic plan should be directed toward determining whether the ferret has pulmonary, cardiac, or extrathoracic disease. Differential diagnoses include heart disease (e.g., cardiomyopathy, valvular disease, dirofilariasis), pleural effusion, pulmonary edema, intrathoracic neoplasia (e.g., mediastinal lymphoma), canine distemper, influenza, or pneumonia. The following have been re-

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Small Animal/Exotics

TABLE I Diagnostic Differentials and Initial Diagnostic Plan by Clinical Signs Differential Diagnosis Dyspnea Pneumonia Cardiomyopathy Dirofilariasis Mediastinal lymphoma Canine distemper Influenza Weakness (“the flat ferret”) Cardiomyopathy Hypoglycemia, insulinoma Hyperestrogenism Dirofilariasis Influenza Neoplasia, lymphosarcoma, other Canine distemper Nausea, Vomiting, Anorexia Foreign body ingestion Trichobezoars Helicobacter Megaesophagus Metabolic disease Insulinoma Diarrhea Campylobacter Epizootic catarrhal enteritis Helicobacter Proliferative enteritis Rotavirus Salmonella Parasitism Gastrointestinal lymphoma, other neoplasm Urethral Obstruction, Dysuria Prostatomegaly Urinary calculi

Initial Diagnostic Plan Complete blood count Serum chemistry and electrolytes Thoracic radiography Electrocardiogram Echocardiogram Thoracocentesis Tracheal wash Hematocrit/total solids (stat.) Blood glucose (stat.) Serum chemistry and electrolytes Abdominal radiography Thoracic radiography Distemper immunofluorescence antibody on conjunctival scrape Blood glucose (stat.) Complete blood count Serum chemistry and electrolytes Abdominal radiography

Complete blood count Serum chemistry and electrolytes Specific cultures Fecal floats, smears Abdominal radiography Abdominal ultrasound

Hematocrit/total solids (stat.) Complete blood count Serum chemistry and electrolytes Urine culture Urinalysis Abdominal radiography Abdominal ultrasound

ported: bacterial pneumonia caused by Streptococcus zooepidemicus, Streptococcus pneumoniae, and streptococci groups C and G; Klebsiella species; Pseudomonas species; Escherichia coli; and, rarely, fungal pneumonia caused by Blastomyces dermatitidis (Figure 1) and Coccidioides immitis.6–8

Thoracic radiographs are essential to determine whether intrathoracic disease is present. Thoracocentesis may be both diagnostic and therapeutic. Electrocardiography is useful in the diagnosis of arrhythmia, and echocardiography is indicated in patients with suspected heart disease. A quick assessment of hematocrit and total solids helps to rule out anemia, and a complete blood count can help to establish a diagnosis of infectious or neoplastic disease. Transglottal tracheal wash, although useful in establishing the presence of pathogens in the lower airway, is limited by the relatively small size of the trachea (i.e., 2.5 to 3.5 mm in diameter). The approach is made through the oropharynx, and contamination is difficult to avoid. Dyspneic ferrets must be monitored closely throughout the diagnostic work to avoid undue stress. A severely dyspneic ferret may tolerate only oxygen therapy and initial furosemide therapy. Placement of a patent intravenous catheter is a priority in order to facilitate administration of medications if respiratory or cardiac arrest occurs.

WEAKNESS AND HEMIPARESIS Ferrets are often presented for hindlimb paresis or paralysis; the condition can be associated with a wide variety of causes, but primary spinal disease is rare. A minimum diagnostic database (i.e., complete blood count, serum chemistry and electrolytes, and radiographs of the chest and abdomen) should be gathered. Insulinoma, lymphosarcoma, anemia, and thoracic disease are the most common causes of weakness. Placement of an intravenous or intraosseous catheter for replacement of fluid deficits during a 24-hour period is important.

NAUSEA, VOMITING, AND DYSPHAGIA Differential diagnoses for vomiting include obstructive disease (e.g., foreign body, trichobezoar, neoplasm), megaesophagus (Figure 2), helicobacterial gastritis, inflammatory bowel disease, and insulinoma. Palpation and abdominal radiographs can usually determine whether obstructive disease is pres-

INTRATHORACIC DISEASE ■ THORACOCENTESIS ■ AVOIDANCE OF STRESS

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TABLE II Formulary Drug

Dose

Route

0.1 mg once daily

PO

2–4 mg/kg

IV, IM

0.5 mg/kg every other day

PO

Cardiomyopathy

0.5–2 mg/kg

IV

Shock

Diazepam20

1–2 mg/kg

IM

Seizure control, tranquilization

Doxapram21

5–11 mg/kg

IV

Respiratory stimulant

Gonadotropinreleasing hormone22

20 mc/ferret; repeat in 2 weeks if necessary

IM

Induce ovulation Terminate estrus

Human chorionic gonadotropin22

100 IU/ferret; repeat in 2 weeks if necessary

IM

Stimulate ovulation, terminate estrus

Digoxin

9

Furosemide 9 Enalapril9 Dexamethasone 9 NaPO4

Indication Cardiomyopathy Abdominal or thoracic effusion, pulmonary edema

Most ferrets with gastrointestinal disease have the primary signs of anorexia and nausea, as opposed to vomiting. Nausea may be exhibited as ptyalism, lip smacking, and bruxism. Hypoglycemia in ferrets can also manifest as ptyalism, pawing at the mouth, and dysphagia. The blood glucose level should be determined: if it is less than 40 mg/dl, or if the ferret is clinically weak, an oral sugar solution or intravenous dextrose should be given. Administration of these substances before collection of diagnostic samples interferes with diagnosis. Ferrets with insulinoma may develop electrolyte imbalances, especially hypokalemia; therefore, electrolytes should be monitored during dextrose therapy.

DIARRHEA Diarrhea in ferrets may be a result of infection (e.g., Cam0.25–2 mg/kg PO Hypoglycemia Prednisone19 pylobacter species, Salmonella species, Helicobacter mustelae, IV = intravenous; IM = intramuscular; SC = subcutaneous; PO = oral. parasites, epizootic catarrhal enteritis, rotavirus) or some othent; an obstruction mandates immediate surgical interer disorder (e.g., proliferative enteritis, eosinophilic envention. Young ferrets are notorious for ingesting forteritis). Ferrets with diarrhea can become profoundly eign matter, particularly rubber items. dehydrated and therefore require emergency supportive Ferrets that have no evidence of obstructive disease care. The high metabolic rate and short gastrointestinal can receive antiemetics, such as metoclopramide, to retransit time in these animals contribute to rapid dehyduce fluid loss. Electrolyte abnormalities in clinically dration. The initial diagnostic plan includes abdominal dehydrated animals must be radiographs or ultrasonography corrected. Intravenous or in(or both) to rule out obstructraosseous fluid therapy is mantive disease. A complete blood datory in patients with modcount and serum chemistry erate to severe dehydration, panel are necessary to evalualthough mild dehydration ate the ferret’s metabolic stamay be managed with subcutus, although these tests rarely taneous fluid administration. provide a diagnosis. Initiating Supportive care should be treatment with broad-specprovided until surgical correctrum antibiotics pending cultion of obstructive disease, or ture and sensitivity data is medical management of unreasonable, given the number derlying medical conditions, Figure 1—Radiographic appearance of blastomycosis in a of bacterial enteritides that ferret. can be instituted. can affect domesticated ferLactated Ringer’s solution

100 ml/kg 60–80 ml/kg

IV IV, SC

Shock dose Fluid therapy

OBSTRUCTIVE DISEASE ■ FLUID THERAPY ■ HYPOGLYCEMIA

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Figure 2—Contrast esophagram of a ferret with megaesopha-

gus. Figure 3—Ultrasonogram of an enlarged cavitated prostate in

rets. If culture results are negative, antibiotics should be discontinued.

a hob with hyperadrenocorticism.

istry panel with electrolytes, and urinary cultures are inURETHRAL OBSTRUCTION dicated if active urinary sediment is present. Urethral obstruction is primarily a disease of male ferEstablishment of a patent intravenous fluid line, rapid rets (hobs) but has also been reported in females (jills).9 resolution of hyperkalemia, and establishment of urine Urinary obstruction in hobs has been associated with flow is critical to short-term survival of the patient. Hobs prostatomegaly secondary to adrenal disease and hyperanand jills may be catheterized with a 3.5-Fr red rubber drogenism9 (Figure 3). Cystic and urethral calculi (Figure catheter.10 Passing a urinary catheter in a hob can be 4) are common; struvite (i.e., challenging because the uremagnesium ammonium phosthral opening is small and difphate) crystals are the most ficult to locate. Prostatomegaly common. Bacterial cystitis may impede placement of the may accompany cystic calculi. urinary catheter, and general Anamnesis includes stranguria, anesthesia is recommended for dysuria, pollakiuria, and often adequate urethral relaxation. hematuria. Ferrets with struIn cases of recalcitrant urethral vite crystals often have a histostones or plugs, careful cystory of an inappropriate diet, centesis, followed by cystotosuch as dog food or low-qualimy with antegrade urethral ty adult cat food. flushing, may be the only reA large, turgid bladder is course. If this fails, the clinievident on physical examinacian should be prepared to pertion, although not all hobs form perineal urethrostomy. with prostate enlargement Ferrets with prostatomegaly have complete urinary tract usually have adrenal cortical obstruction. The initial diaghyperplasia, adenomatous nostic plan includes abdomichanges, or adenocarcinoma nal radiographs, ultrasonograwith overproduction of androphy, or both and assessment gens. The neoplastic or hyperand correction of electrolyte plastic adrenal gland must be and acid–base abnormalities. removed to effect a resolution. Ferrets may be acidotic and Uncomplicated hyperplasia of hyperkalemic if the obstructhe prostate usually resolves to tion has persisted for more the point where the animal than 12 to 24 hours. Com- Figure 4—Urethral calculi in a hob. The stones have filled can urinate without difficulty the urethra proximal to the os penis. plete urinalysis, serum chemin a few days.9 Prostatitis and PROSTATOMEGALY ■ ADRENAL DISEASE ■ CYSTOCENTESIS

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Compendium March 2000

prostatic cysts carry a poorer prognosis. Transmural bacterial migration with septic peritonitis has a poor prognosis.

of whole blood from one or more donors. To date, distinct blood groups have not been identified in ferrets, making the likelihood of an adverse ANEMIA transfusion reaction low.12 Ferrets that have had signifSevere depression of the icant or prolonged hemorhematocrit can preclude imrhage (e.g., gastrointestinal mediate ovariohysterectomy bleeding; trauma; ingestion of in jills with persistent estrus vitamin K antagonist rodentiand hyperestrogenemia. Ovucides; and, on rare occasions, lation should be induced in adrenal gland disease) present Figure 5—Swollen vulva in a jill with hyperestrogenism. these patients with human with weakness secondary to chorionic gonadotropin or anemia. Jills in prolonged esgonadotropin-releasing hortrus with hyperestrogenemia and resultant aplastic anemone injections, and periodic blood transfusions mia may be severely anemic with a hematocrit less than should be given until the ferret has stabilized. 12 (Figure 5). Anamnesis may reveal that a jill has been CARDIOMYOPATHY in estrus for several months or that it has a history of Dilated cardiomyopathy is the most common cardiac trauma or melena. The initial diagnostic plan includes problem in adult ferrets.1,13,14 This disorder is usually immediate measurement of the hematocrit and total seen in older ferrets with a history of coughing, weaksolids, a complete blood count, thoracic and abdominal ness, hindlimb paresis, vomiting, anorexia, and/or radiographs, and abdominocentesis to rule out internal weight loss. Signs of heart failure in ferrets are similar to bleeding. those in other mammals, including tachypnea, tachycarIsoflurane anesthesia can have adverse effects on the dia, ascites, hepatomegaly, pulmonary edema, hypotherhemogram of ferrets by sequestering erythrocytes in the mia, cyanosis, weakness, posterior paresis, and thready spleen, which may exacerbate poor oxygen-carrying capulses.1,15 A holosystolic murmur and crackles can be pacity in anemic ferrets.11 Initial stabilization includes intravenous or intraosseous catheterization and transfusion auscultated at the seventh or eighth intercostal space.1 The initial diagnostic plan includes chest radiographs; electrocardiography; and, when possible, echocardiography. The normal radiographic appearance of the cardiac silhouette in ferrets is more globoid than that of cats. Radiographic signs include pulmonary venous congestion, pulmonary edema, and pleural effusion1 (Figure 6). The most common electrocardiographic finding is

Figure 6A

Figure 6B

Figure 6—(A) Ventrodorsal and (B) lateral radiographs of cardiomyopathy and pulmonary edema in a ferret.

HYPERESTROGENISM ■ BLOOD TRANSFUSION ■ HEART FAILURE

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Small Animal/Exotics

sinus tachycardia, although ventricular premature complexes and atrial premature complexes are occasionally recorded. Tall R waves, QRS prolongation, and ST depression have also been reported with this disease.16 Echocardiographic findings are likely to include increased left ventricular end-diastolic and end-systolic dimensions, decreased fractional shortening, an enlarged left atrium, mitral regurgitation, and right ventricular enlargement.1,17 Initial management includes supplemental oxygen and furosemide for diuresis. Thoracocentesis can be useful for therapy and diagnosis. Digoxin is indicated for supraventricular tachyarrhythmia and myocardial failure. Enalapril is recommended as a balanced vasodilator.1,18

INSULINOMA Pancreatic beta-cell tumors and the associated hyperinsulinemia are very common.19–22 Ferrets are often presented shortly after a hypoglycemic episode. Ferrets with hypoglycemia are dull, stuporous, ataxic, dehydrated, and hypothermic and salivate excessively. 22 Blood glucose levels measured during a hypoglycemic crisis are usually less than 60 mg/dl. Blood glucose levels of animals that present after resolution of the hypoglycemic episode may be in the 60- to 90-mg/dl range.

Diagnosis of insulinoma when the blood glucose level is greater than 70 mg/dl requires evaluation of the insulin–glucose ratio. Nutrical® (EVSCO Pharmaceuticals, Buena, NJ), corn syrup, or 50% dextrose may be applied to the oral mucous membranes of a hypoglycemic ferret. Placement of an intravenous or intraosseous catheter facilitates glucose administration. A large bolus of glucose may cause a rebound release of insulin. The goal of therapy is to return the ferret to a euglycemic state, as opposed to a hyperglycemic state. Prednisone antagonizes the effects of insulin and helps to maintain euglycemia. Fluid deficits should be corrected, and supplemental potassium should be administered as dictated by serum electrolyte evaluation. Correction of hypoglycemia, dehydration, and electrolyte imbalances is generally followed by surgical excision of the islet cell tumors.

SUMMARY This article describes some of the diseases of ferrets that are commonly seen in a critical care setting. Clinicians should focus on ferret-specific diseases and causes mentioned here, but their experience with dogs and cats can also provide useful guidance through diagnosis and therapy for critically ill ferrets.

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About the Authors Dr. Benson is a resident in Zoological Medicine, School of Veterinary Medicine, University of California, Davis, California. Dr. Ramer is a staff veterinarian at the Indianapolis Zoo, Indianapolis, Indiana. Dr. Paul-Murphy is the chief of service of the Special Species Health Service at the School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin.

REFERENCES 1. Stamoulis ME: Cardiac diseases in ferrets. Semin Avian Exotic Pet Med 4:43–48, 1995. 2. Brown SA: Ferrets, in Jenkins JR, Brown SA (eds): A Practitioner’s Guide to Rabbits and Ferrets. Lakewood, CO, American Animal Hospital Association, pp 43–111, 1993. 3. Hillyer EV: Ferret endocrinology, in Kirk RW, Bonagura JD (eds): Current Veterinary Therapy XI Small Animal Practice. Philadelphia, WB Saunders Co, 1992, pp 1185–1186. 4. Hillyer EV, Brown SA: Ferrets, in Birchard SJ, Scherding RG (eds): Saunders’ Manual of Small Animal Practice. Philadelphia, WB Saunders Co, 1994, pp 1317–1344. 5. Carpenter JW, Mishima TY, Rupiper DJ: Exotic Animal Formulary. Manhattan, KS, Greystone Publications, 1996. 6. Fox JG: Bacterial and mycoplasmal diseases, in Fox JG (ed): Biology and Diseases of the Ferret. Philadelphia, Lea & Febiger, 1988, pp 197–216. 7. Fox JG, Pearson RC, Groham JR: Virals and chlamydial diseases, in Fox JG (ed): Biology and Diseases of the Ferret. Philadelphia, Lea & Febiger, 1988, pp 217–234. 8. Du Val-Hudelson KA: Coccidiomycosis in three European ferrets. J Zoo Wildl Med 21:353–357, 1990. 9. Hillyer EV: Urogenital diseases, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits and Rodents—Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 44–53.

10. Marini RP, Esteves MI, Fox JG: A technique for catheterization of the urinary bladder in the ferret. Lab Anim 28: 155–157, 1994. 11. Marini RP, Jackson LR, Esteves MI, et al: Effect of isoflurane on hematologic variables in ferrets. Am J Vet Res 55: 1479–1483, 1994. 12. Manning DD, Bell JA: Lack of detectable blood groups in domestic ferrets: Implications for transfusion. JAVMA 197: 703–707, 1990. 13. Stamoulis ME, Miller MS, Hillyer EV: Cardiovascular diseases, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits and Rodents—Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 63–76. 14. Miller MS: Ferret cardiology. Proc North Am Vet Conf :735, 1993. 15. Greenlee PG, Stephens E: Meningeal cryptococcosis and congestive cardiomyopathy in a ferret. JAVMA 184:840, 1984. 16. Smith SH, Bishop SP: The electrocardiogram of normal ferrets, and ferrets with right ventricular hypertrophy. Lab Anim Sci 35:268, 1985. 17. Lipman N, Fox JG: Clinical, functional, and pathologic changes associated with a case of dilatative cardiomyopathy in a ferret. Lab Anim Sci 37:210, 1987. 18. Ensley PK, Van Wickle T: Treatment of congestive heart failure in a ferret. J Zoo Wildl Med 13:23, 1982. 19. Elie MS, Zerbe CA: Insulinoma in dogs, cats, and ferrets. Compend Contin Educ Pract Vet 17(1):51–59, 1995. 20. Caplan ER, Peterson ME, Mullen HS, et al: Diagnosis and treatment of insulin-secreting pancreatic islet cell tumor in ferrets: 57 cases (1986–1994). JAVMA 209:1741–1745, 1996. 21. Ehrhart N, Withrow SJ, Ehrhart EJ, Wimsatt JH: Pancreatic beta cell tumors in ferrets: 20 cases (1986–1994). JAVMA 209:1737–1740, 1996. 22. Kaufman J, Schwarz P, Mero K: Pancreatic beta cell tumor in a ferret. JAVMA 185:998–1000, 1984.