Heartworm and Wolbachia: Therapeutic implications

A safer, more effective adulticidal treatment and a safe method for reducing microfilaremia and breaking transmission of heartworm disease early in the treatment are needed. The present study evaluated efficacy of ivermectin (I) doxycycline (DOXY) alone or together (with Or without melarsomine [MEL]) in dogs With induced adult heartworm infection and assessed the ability of microfilariae front DOXY-treated dogs to develop to L-3 in Aedes aegypti mosquitoes and subsequently to become reproductive adults in dogs. Thirty beagles were each infected with 16 adult heartworms by intravenous transplantation. Six weeks later, dogs were ranked by microfilarial count and randomly allocated to 6 groups of 5 clogs each. Beginning oil Day 0, group I received IVM (6 mcg/kg) weekly for 36 weeks. Group) 2 received DOXY ( 10 mcg/kg, day)) orally Weeks 1-6, 10-11, 16-17, 22-25. and 28-33. Groups 3 and 5 received IVM and DOXY according to closes and schedules Used for Groups 1 and 2. At Week 24, Groups 3 and 4 received all intramuscular injection of MEL (2.5 mg/kg,). Followed I month later by two injections 24 It apart. Group 6 was not treated. Blood samples were collected for periodic microfilaria counts and antigen (Ag) testing (and later immunologic evaluation and molecular biology procedures). Radiographic and physical examinations. hematology/clinical Chemistry testing and urinalysis were done before infection. before Day 0. and periodically during the treatment period. At 36 weeks, the dogs were euthanized and necropsied tor worm recovery. collection of lung, liver, kidney, and spleen samples for examination by immunohistochemistry and conventional histological methods. All dogs treated with IVM + DOXY (without MEL) were amicrofilaremic after Week 9. Microfilarial counts gradually decreased in dogs treated with IVM or DOXY. but most had a few microfilariae at necropsy. Microfilarial counts for dogs treated only with MEL were similar to those for controls. Antigen test scores gradually decreased with IVM + DOXY (With Or Without MEL) and alter MEL. Anti-en scores Cor IVM or DOXY alone were similar to controls throughout the study. Reduction of adult worms was 20.3% For IVM, 8.7% for DOXY, 92.8% for IVM + DOXY + MEL. 100% Cor MEL, and 78.3% For IVM + DOXY. Mosquitoes that fed oil blood from DOXY-treated dogs had L; normal in appearance but Were not infective for dogs. Preliminary observations suggest that administration of DOXY + IVM tor several Months Prior to (or Without) MEL will eliminate adult HW with less potential for severe thromboembolism than MEL alone. reserved. (C) 2008 Elsevier B.V. All rights