Heartworms or Dirofilaria immitis are a spaghetti-type worm that develop in the heart and lungs of an infected host. The disease is transmitted by the bite of a mosquito. Due to the insect vector, disease is more common in mild, moist climates. Mosquitos appear to infect ferrets with heartworms at a similar rate as seen in the dog.

Most infected ferrets will appear asymptomatic (do not show any overt clinical signs of disease) until one of two critical periods in the heartworm life cycle occur. Typical clinical signs when they develop will mimic those seen in the cat and will include: collapse, dyspnea (difficult breathing), coughing, pale mucous membranes, vomiting, and sudden death. Neurologic clinical signs such as ataxia (unbalanced), blindness, circling, dementia, and seizures may also occur, usually due to aberrant worm migration. Aberrant migration occurs when an adult worm migrates to another part of the body rather than the heart, often lodging alternatively in the brain. Clinical signs of right heart failure may also be exhibited such as ascites (fluid in the abdomen) or pitting edema of the extremities (legs).

In the ferret, there is inflammation in the pulmonary arteries and lung tissue as immature worms develop in the body of their host. This reaction typically occurs 70 to 80 days after being infected by a mosquito. This inflammation may produce an asthma-like response.

The second critical state for a ferret is when an adult worm dies and degenerates within the host. The degeneration of the adult heartworm will cause more pulmonary (lung) inflammation, thromboembolism (the formation of blood clots and parasitic emboli resulting in the obstruction of a blood vessel), and anaphylaxis (exaggerated allergic reaction). Anaphylaxis or vessel occlusion of a major vessel (embolus) is the most likely causes of sudden death in ferrets due to heartworms.

Microfilaria (immature baby heartworms) are not consistently found in blood smears from infected ferrets. When microfilaria are demonstrated in the blood, it is diagnostic.

There are presently no serologic tests available for the detection of ferret heartworm disease. Other useful diagnostic tests include a CBC or complete blood count. The number of eosinophils and basophils (types of white blood cells) may be increased with a parasitic infection. Chest radiographs may show characteristic changes in the heart and lungs that may be relevant to heartworm infection. Echocardiography may demonstrate adult heartworms as well as their resulting pathology on the heart itself.

Treatment is primarily supportive. Prednisone may prove helpful, especially in decreasing lung inflammation and coughing. Oxygen supplementation may be necessary when breathing is labored. Tetracycline use, for complicating bacteria called Wolbachia spp., is also advocated in the hope of decreasing inflammatory mediators.

Prevention is the best way to avoid infection in ferrets when living in endemic areas. Outdoor ferrets are at greatest risk of infection. Indoor ferrets are also susceptible to infection as the disease may be caused by exposure to only one mosquito.

Monthly heartworm preventatives are available for use in the cat and can be used in the ferret, in the kitten size. Although not approved specifically for use in the ferret, the topical feline products such as Feline Revolution® manufactured by Pfizer and Advantage Multi® marketed by Bayer Animal Health should be used on a monthly basis regardless of whether a ferret lives indoors or out.

Ferrets with heartworm infection should also be prescribed a monthly preventative in conjunction with prednisone when respiratory clinical signs are present. Prognosis once clinical signs of disease are present is poor.

References:

“Antech Diagnostics News.” March 2007.

Atkins, Clarke; “Understanding Feline Heartworm Disease”, Parasite Developments. Proceedings from the 2007 NAVC Conference and the 2007 Western Veterinary Conference. Supplement to Veterinary Forum Vol.24.No.3 (A). March 2007.pp 2-7.

Dillon, Ray. “The Nature of Heartworm Disease in Cats: Different from Dogs”. Parasite Developments. Proceedings from the 2007 NAVC Conference and the 2007 Western Veterinary Conference. Supplement to Veterinary Forum. Vol.24 No.3 (A). March 2007.pp. 16-18.

NAVC Clinician’s Brief. November 2007. P. 72.

Schaper, Heine, Arther, RG, el al. Parasitol Res 101:557-562, 2007.

Fox, J.G. Biology and Diseases of the Ferret. Lea and Febiger. Philadelphia. 1988. Pp. 244-245.