摘要 : The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L₃ and L₄ of <i>Brugia pahangi</i> and <i>Litomosoides sigmodontis</i> in rodent mode... 展开 The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L₃ and L₄ of <i>Brugia pahangi</i> and <i>Litomosoides sigmodontis</i> in rodent models. Tetracyclines are also now known to have activity against microfilariae and adult <i>Dirofilaria immitis</i>, but assessment of their activity against larval and juvenile heartworms has not been reported previously. This study assessed the effects of doxycycline administered orally at 10 mg/kg twice daily for 30-day periods at selected times during the early part of the life cycle of <i>D. immitis</i> in dogs with dual infections of <i>D. immitis</i> and <i>B. pahangi</i>. Twenty beagles were randomly allocated by weight to four groups of five dogs each. On Day 0, each dog was given 50 <i>D. immitis</i> L₃ and 200 <i>B. pahangi</i> L₃ by SC injection. Dogs received doxycycline on Days 0-29 (Group 1); Days 40-69 (Group 2); or Days 65-94 (Group 3). Group 4 served as untreated controls. Blood samples were collected for microfilariae counting and antigen testing. Necropsy for collection of adult heartworms and selected tissues were performed Days 218-222. Heartworms recovered were examined by immunohistology, conventional microscopy/transmission electron microscopy, and molecular biology techniques. No live heartworms were recovered from dogs in Group 1; dogs in Group 2 had 0 to 2 live worms (98.4% efficacy), and dogs in Group 3 had 0-36 live worms (69.6% efficacy). All control dogs had live adult heartworms (25-41). The live worms recovered from dogs in Groups 2 and 3 were less developed and smaller that worms from control dogs. Microfilariae were not detected in any dogs in Groups 1 and 2; one dog in Group 3 had 1 microfilariae/ml at necropsy. All control dogs had microfilariae at necropsy. One dog in Group 1 was antigen positive at one sampling (Day 166). One dog in Group 2 was antigen positive Days 196 and 218-222 and three dogs in Group 3 were antigen positive at one or more samplings All five control dogs were antigen positive at all three sampling times. These findings suggest that doxycycline at 10 mg/kg orally twice daily for 30 days has efficacy against migrating tissue-phase larvae and juvenile worms and will delay or restrict microfilarial production. 收起