Abstract
Canine heartworm disease is a life-threatening disease caused by Dirofilaria immitis and is prevalent in Brazil. The standard drug for its treatment, melarsomine dihydrochloride, is a fast-killing organic arsenical chemotherapeutic agent not approved in Brazil. Therefore, an alternative strategy, such as macrocyclic lactone in combination with a tetracycline antibiotic, has to be used. The alternative method is a long-term therapy that could lead to compliance issues during treatment. The aim of this case report is to present a preliminary assessment on the efficacy and safety of an off-label biannual administration of slow-release moxidectin (0.5 mg/kg every 6 months), which is formulated for annual administration (0.5 mg/kg annually). This overdose was chosen to test if moxidectin serum levels could be maintained high enough to harm the worms. It was administered to a 4-year-old female dog in combination with a 30-day doxycycline course. The second dose of moxidectin was administered approximately a week before she gave birth to three healthy puppies. Microfilariae were not detected on day 180 of treatment. Serological tests showed that the worms were eliminated, as two negative antigen tests were obtained 6 months apart (at day 180 and day 360 of treatment). Therefore, the off-label biannual use of moxidectin in combination with doxycycline was effective in eliminating D. immitis in 360 days and was harmless for the pregnant dog and her offspring, suggesting that this strategy is promising. Although these results are encouraging, further studies are needed to confirm safety and efficacy issues.
Highlights
Canine heartworm disease is life threatening when left untreated [1, 2]; treatment must be administered even under adverse conditions
The results showed that she had asymptomatic D. immitis infection as indicated by the presence of microfilariae in Knott’s modified test [17] and a positive D. immitis antigen test, seronegative for Anaplasma spp., Ehrlichia spp., and Borrelia burgdorferi (SNAP R 4DX Plus R, IDEXX Laboratories Inc., Westbrook, ME, USA)
Since a D. immitis-infected dog receiving alternative treatment must present microfilariae and D. immitis antigen test negative results 6 months apart to confirm the elimination of the parasite, a second moxidectin injection (0.5 mg/kg) was administered 6 months after the first and the animal was kept under observation
Summary
Canine heartworm disease is life threatening when left untreated [1, 2]; treatment must be administered even under adverse conditions. The antibiotic with best therapeutic results is doxycycline [9] and the macrocyclic lactones reported as efficacious are oral ivermectin [10,11,12], topical moxidectin [13, 14], and double annual dose of injectable moxidectin [15] This long-term treatment is called “alternative treatment,” “slow kill,” “soft kill,” “doxy-moxi,” or “moxi-doxy” and is recommended to be used when the arsenical drug is unavailable or when fast kill is contraindicated [2, 7]. Since a D. immitis-infected dog receiving alternative treatment must present microfilariae and D. immitis antigen test negative results 6 months apart to confirm the elimination of the parasite, a second moxidectin injection (0.5 mg/kg) was administered 6 months after the first and the animal was kept under observation. Doppler echocardiogram, and chest X-rays were unchanged when she was presented 6 months after the second moxidectin dose and serological tests with the heat pre-treatment sample [18] confirmed that heartworm had been successfully eliminated. Since the animal was free of infection, the owner was advised to continue with the moxidectin injections annually
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