Thoracic Disease in the Ferret

Heidi L. Hoefer, DVM, ABVP
West Hills Animal Hospital
Long Island Veterinary Specialists
Huntington, New York

Cardiomyopathy

Cardiac disease is common in middle-aged and older domestic ferrets (Mustela putorius furo). Dilated cardiomyopathy (DCM) is most common but hypertrophic cardiomyopathy (HCM) and acquired valvular disease can be a problem. Ferrets are also susceptible to heartworm disease caused by Dirofilaria immitus. Clinical presentation ranges from an asymptomatic, incidental finding to fulminant heart failure.

Ferrets with advanced heart disease are generally weak. Respiratory rate may be increased, especially if thoracic effusions are present. Heart murmurs are common with dilated cardiomyopathy and relatively uncommon with the hypertrophic form and tachy-arrhythmias can be seen with either form of cardiomyopathy. Coughing is rare.

Diagnosis of heart disease involves imaging techniques. Thoracic films reveal an enlarged, globoid heart with increased sternal and diaphragmatic contact with DCM but the heart can be normal in size with HCM. Pleural effusion may be present and in some cases, is so extensive that the heart is not visualized. Be tentative with the initial diagnosis in cases of severe effusion, there may be an imperceptible mass. Varying degrees of pulmonary edema are often present. The liver and spleen are usually enlarged from passive congestion. Ascites is uncommon.

Echocardiography is the most important part of the cardiac workup in the ferret. Pleural and pericardial effusions are readily seen and it can determine if an underlying mass is present.

In general, treatment for heart disease in ferrets follows the same therapeutic guidelines used in dogs and cats. Pharmacokinetic studies have not been done for cardiovascular drugs in ferrets; scaling down doses already in use for cats works well clinically.

Furosemide (Lasix, Hoechst-Roussel) at 2-3 mg/kg IM or IV q 8-12h is used initially for ferrets in fulminant myocardial failure and at 1-2 mg/kg PO q 12h for long term maintenance therapy. Vasodilators are an important part of cardiac therapy. Nitroglycerin 2% cream is a venous dilator that can be used inside the pinna for the first 24 hours of therapy for cardiac failure. Enalapril (Enacard, Merck & Co) is an angiotensin converting enzyme inhibitor used at 0.5 mg/kg PO q 48h initially and can be increased to once daily dosing if tolerated well. Ferrets seem to be very sensitive to this drug and can become quite lethargic if hypotensive. Because enalapril is only available in tablet form, a suspension can be made by a compounding pharmacy.

Digoxin is commercially available in a pediatric elixir (Lanoxin^�, Burroughs-Wellcome) that works well in ferrets with dilated cardiomyopathy at 0.01 mg/kg q 24h initial dose. The digoxin dose can be gradually increased to twice daily if needed. Beta-blockers like atenolol or calcium channel blockers (diltiazem) can be useful to slow heart rate in cases of hypertrophic cardiomyopathy. Follow dosing schedule for the cat. Watch for lethargy and inappetance as potential side effects.

Heartworm Disease

Ferrets in heartworm endemic areas are susceptible to filariasis. Dirofilaria immitis infection can result in severe cardiac disease in the ferret. Because of the relatively small ferret heart, even a very low parasite burden (one or two worms) can have serious consequences.

Ferrets with natural infections are not microfilaremic. Heartworm testing kits utilizing the enzyme-linked immunosorbent assay (ELISA) antibody test should be used. Some of the newer tests made for cats may be sensitive enough to pick-up occult heartworm infection in the ferret but research in this area has not been conducted. Ultrasound may show the nematodes within the right ventricle or vena cava, but it is an unreliable diagnostic test for dirofilariasis.

Prevention is best achieved by use of ivermectin at 0.02 mg/kg PO or SQ monthly to prevent maturation of the third stage of larval development. The smallest tablet (68ug) of oral ivermectin (Heartgard-30, Merck AgVET) can be dosed at 1/4 tablet PO monthly. These tablets cannot be reused once removed from the wrapper and broken into quarters. The 1% bovine preparation (Ivomec, Merck AgVET) can be used orally following dilution with propylene glycol to achieve a .1 mg/ml solution. The suspension should maintain potency until the expiration date of the ivermectin if kept in an amber bottle and protected from light.

Treatment of dirofilariasis in ferrets is possible but carries a guarded prognosis. Success depends on early diagnosis and long term (4 months) antithrombotic therapy (prednisone).

Neoplasia

Lymphoma is the most common thoracic tumor seen in ferrets. In younger ferrets 10 months -2 years of age, mediastinal masses with effusions are common. These can be difficult to distinguish radiographically from heart failure but the lymphoma ferrets are usually significantly younger. These ferrets often have involvement of the liver and spleen with organomegaly. Diagnosis can be made through thoracocentesis and cytological evaluation of the fluid, or with sonography. Prognosis is very poor with this form of lymphoma.

Other neoplasias can be present in the thorax although primary cardiac, intracardiac or pericardial tumors are rare. Metastatic pulmonary neoplasia is also rare.

Megaesophagus

Idiopathic megaesophagus has been reported in several ferrets. These ferrets are usually middle-aged and present for lethargy, weight loss, regurgitation, gagging, and sometimes coughing and tachypnea. Clinically, these cases can present like a gastritis or gastrointestinal foreign body. On radiographs, the cervical and thoracic esophagus is enlarged and food may be visualized in the lumen. There may be gastric gas and aspiration pneumonia. Motility can be assessed with fluoroscopy or a barium swallow can delineate the esophagus and be evaluated for transit time. Once diagnosed, ferrets with megaesophagus usually decline rapidly and prognosis in general is very poor. Treatment can be attempted using motility modifyers like cisapride or reglan, antimicrobials, gastric antacids (famotidine or cimetidine), and dietary management.

Pneumonia

In general, pneumonias are uncommonly diagnosed in a pet ferret practice. There are many potential bacterial respiratory pathogens and these include Streptococcus zooepidemicus, Pseudomonas aeruginosa, E coli, and Bordetella bronchiseptica. Bacterial pneumonias may be primary, as is seen with juvenile ferrets, or can be secondary to the immunosuppressive effects of viral infections like canine distemper or influenza. Aspiration pneumonia occurs with megaesophagus.

Diagnosis and treatment follow the same guidelines as with other small animals: radiographs, bloodwork, transtracheal washes for cytology and culture, and long term antibiotics. Ferrets tolerate all the common antibiotics used in dogs and cats at similar doses.

References

1.  Fox JG: Other systemic diseases. In Fox JG, ed.: Biology and Diseases of the Ferret (2^nd ed). Philadelphia, Lea & Febiger, 1998, pp 307-320.

2.  Hoefer HL: Heart disease in ferrets. In Bonagura JD, Kirk RW (ed): Current Veterinary Therapy XII. WB Saunders, Philadelphia, 1998.

3.  Rosenthal KL: Respiratory Diseases. In Hillyer EV, Quesenberry KE, ed.: Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia: WB Saunders, 1996, pp 77-84.