Today's Veterinary Practice

JAN-FEB 2018

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PEER REVIEWED 16 PRACTICAL PARASITOLOGY blood cell count should always be performed. Changes commonly seen include elevated liver enzymes, azotemia, bilirubinemia, eosinophilia, basophilia, neutrophilia, nonregenerative anemia, and thrombocytopenia. 3 If D immitis microfilariae are observed on a blood smear ( FIGURE 4 ), the diagnosis of HWD is definitive. However, the Difil ( Vetoquinol.com ) or modified Knott's test can have false-negative results owing to the normally low levels and transient nature of the microfilaremia in ferrets. 13 Molecular genetic structures can be detected on PCR. 3 D immitis can be observed via echocardiography as abnormal hyperechoic structures in the right atrium and/or right ventricle. 14 Nonselective angiography provides a sensitive method of detection of adult heartworms in the cranial vena cava. 15 TREATMENT The decision of which treatment is most suitable for the patient should be based on whether the patient is in heart failure. Stabilization of a ferret in heart failure is similar to that for a cat or dog, administering the following as necessary: ■ Oxygen supplementation ■ Tranquilization of the patient with midazolam 0.1 to 0.3 mg/kg IM 8 ■ Furosemide 1 to 4 mg/kg PO, IM, or IV q6–24h 13 ■ Benazepril 0.25 to 0.5 mg/kg PO q24h 8 ■ Pimobendan 0.5 to 1.25 mg/kg PO q12h 8 Once the patient is stable, the decision to pursue a surgical approach or medical management must be made ( TABLE 1 ). All the published treatment options in ferrets consist of extralabel protocols. Alleviation of clinical signs with prednisone 0.5 mg/kg PO q12h can be elected if the patient is not stable enough for more invasive treatment. 14 Successful transvenous extraction of adult heartworms has been described in a 10-month- old ferret. 16 After the surgery, the patient was medically managed with corticosteroids and a monthly heartworm preventive. 16 If a more conservative approach is warranted, different protocols have been studied. Protocols using melarsomine 2.5 to 3.25 mg/kg IM have been described using a 2- or 3-injection protocol similar to that used in treating dogs. To prevent pain associated with the injections, sedation or anesthesia of the patient is necessary. Strict cage rest is indicated after treatment, as there is a high risk of thromboembolism. The use of a combination of ivermectin 0.05 to 0.2 mg/kg IM every 30 days and prednisone 0.5 mg/kg PO q12h is indicated if the patient has a mild form of infection. 13 Long-term treatment with moxidectin is described to be associated with fewer risks and can result in antigen-negative patients. In a study performed on 10 naturally infected ferrets, moxidectin was used at a dose of 0.17 mg/ferret SC, and 4 ferrets were reported to be antigen-negative after treatment. 17 Because of the small sample size, we hesitate to recommend this protocol as a successful treatment option before further investigation has been performed. However, the longer course of treatment may result in greater endothelial damage from the prolonged presence of the parasites. 18 FIGURE 4. D immitis microfilaria in a canine blood smear. Image courtesy of Dr. Megan Caudill, UGA. Housing a ferret outside is not recommended in areas where heartworm prevalence in cats and dogs is high. Even housing a ferret indoors 100% of the time is not a guarantee that it will avoid infection. In addition to medical prevention of HWD, housing the ferret in a mosquito- free environment is highly desirable.

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