Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.
Issue link: http://todaysveterinarypractice.epubxp.com/i/536673
tvpjournal.com | July/august 2015 | Today's VeTerinary PracTice aHs HearTWorM HoTLine Peer reviewed 81 methods have not been performed in this species. current best practices suggest employing a combination of testing methods to confrm HWd. due to the apparent transient nature of microflaremia in ferrets, microflaria detection is more problematic in ferrets than dogs; however, if found, it is diagnostic. combining heartworm antigen tests with imaging techniques, such as thoracic radiographs, echocardiography, and angiography (to detect adult heartworms in the heart and associated vessels), appears to yield a relatively high and accurate detection rate. False negative antigen tests are presumed to be due to antigenic loads below detectable levels—when lower worm burdens or single sex infections are present—similar to feline and canine infections. evidence of accuracy and effcacy of antibody testing in ferrets is lacking. Clinical Signs clinical signs of HWd in ferrets are outlined in Table 2. Bilirubinuria is the clinicopathologic change detected most consistently in ferrets with HWd and, while more work is necessary to investigate this link, it may prove to be a consistent indicator for the disease. 2,8,9 Imaging Studies a large percentage of ferrets with naturally occurring HWd have radiographic changes consistent with pleural effusion; additional imaging fndings include tortuous and dilated pulmonary vasculature, right atrial and ventricular enlargement and dilation, and tricuspid regurgitation. 7,10 TREATMENT Treating ferrets with heartworms has proven problematic. as with cats, no treatment has been approved for HWd in ferrets; therefore, treatment options (Table 3, page 82) consist of extra-label protocols. Adulticide Therapy a study in which canine doses of melarsomine dihydrochloride (2.5 mg/kg) were administered intramuscularly 2 times, 24 hours apart, demonstrated approximately 70% effcacy in killing adult heartworms in ferrets. 2 However, the treatment worsened both cardiac and respiratory signs in the ferrets. Melarsomine administered intramuscularly to ferrets at a higher dose of 3.25 mg/kg was found to be equally effective (80.6%−83.3%) when administered either: 2 • Twice, 24 hours apart, or • as one injection, followed one month later by 2 injections, 24 hours apart. comparison of these 2 treatment methods was hindered by the small sample size, and statistical signifcance is diffcult to confrm until a larger population is studied. Macrocyclic Lactone Therapy a small study of adulticides that compared administration of ivermectin (Heartgard, us.merial.com) alone to ivermectin in combination with melarsomine suggested that ferrets may have a higher survival rate when ivermectin is administered alone. However, this study's small sample size makes the signifcance of mortality rates, survival times, and comorbid conditions diffcult to interpret. 2 anecdotally, moxidectin (ProHeart, zoetisus .com) has been used at 0.17 mg/animal in a small number of heartworm antigen-positive ferrets, with Table 2. typical Clinical & laboratory signs of Heartworm Disease in Ferrets 2 Bilirubinuria Biliverdinuria (in cases of caval syndrome) Coughing Cyanosis Decreased appetite/weight loss Dyspnea Enlarged abdomen and liver Exercise intolerance Heart murmur Lethargy Pleural effusion (modifed transudate) Posterior paresis Vomiting Figure. Necropsy of a ferret with heartworm disease.