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| | when prophylactic drugs are administered at the recommended | | when prophylactic drugs are administered at the recommended |
| | doses. | | doses. |
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| − | ==Prevention==
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| − | Heartworm infection is completely preventable with macrolide prophylaxis. Preventive therapy in dogs is recommended beginning at 6-8 wk of age. No testing is necessary at this age. When started at ~1 yr of age, an antigen test is recommended. Before starting a prophylactic regime, all mature dogs that may have been infected >7 mo earlier should be antigen tested and, in appropriate instances, tested for presence of microfilariae. The determination of HW status before starting chemoprophylaxis will avoid unnecessary delay in detecting subclinical infections, and potential confusion concerning effectiveness of the preventive program, if a pre-existing infection becomes evident after beginning chemoprophylaxis. Year-round prevention is advised, but in northern climates, chemoprophylaxis is often initiated in the spring and continued through November. Year-round macrolide administration will arrest the development of larval stages (L3 and L4) that might have occurred prior to preventative initiation or when monthly doses were missed.
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| − | The macrolide preventives ivermectin, milbemycin oxime, moxidectin, and selamectin are safe and effective as prescribed for all breeds. Ivermectin/pyrantel pamoate (hookworms and roundworms) and milbemycin (hookworms, roundworms, and whipworms) also provide control of intestinal nematodes. Milbemycin, however, kills microfilariae (L1) quickly and shock can occur in the face of high microfilarial concentrations. Thus, milbemycin is not administered as a preventive in dogs with microfilariae. Selamectin is administered topically at a monthly dosage of ~6 mg/kg and also kills adult fleas and prevents flea eggs from hatching for 1 mo. It also is indicated for the treatment and control of Otodectes cynotis in dogs and cats, sarcoptic mange, Dermacentor variabilis infestations in dogs, Ancylostoma tubaeforme , and Toxocara cati in cats.
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| − | Annual antigen testing is recommended because overall owner compliance with macrolide prophylaxis is only ~50%. The injectable form of moxidectin is effective for at least 6 mo following 1 injection but use in microfilaremic dogs is not advised. At the time of publication, this formulation was not available in the USA because of concerns regarding toxicity in dogs. With macrolide administration for 6 mo and longer, microfilariae production by female worms ceases and antigen testing is required for detection of infection.
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| − | Heartworm prevention is recommended for all cats in endemic regions, regardless of housing status, because of the potential severe consequences. Ivermectin for cats is safe and effective at 25 µg/kg, PO, once monthly. At this dose, the formulation is also effective against Ancylostoma tubaeforme and A braziliense . Preventive treatment should be initiated in all adult cats, in kittens 6 wk of age, and continued lifelong. Annual antigen and antibody testing is of limited value in cats receiving prophylaxis.
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| | ==Prognosis== | | ==Prognosis== |