Efficacy of oral, topical and extended-release injectable formulations of moxidectin combined with doxycycline in Dirofilaria immitis naturally infected dogs

Abstract

Background Several studies in both experimentally and naturally infected dogs have reported the adulticide effect of a combination of macrocyclic lactones and doxycycline against Dirofilaria immitis, showing that these protocols can be used as an alternative to melarsomine. The present study evaluated the efficacy of oral, topical and extended-release injectable formulations of moxidectin when combined with doxycycline in dogs naturally infected with D. immitis from a shelter located in southern Italy. Methods Thirty dogs with naturally acquired D. immitis infection were divided in three groups (G) and treated with oral moxidectin (G1) once a month for 9 consecutive months, topical moxidectin (G2) once a month for 9 consecutive months or extended release moxidectin injectable (G3) at enrolment and again at 6 months (Day 180). All treatment groups received doxycycline for the first 30 days. Microfilarial concentrations in 1 ml (mff/ml) blood were determined monthly for 9 months with the modified Knott’s test. A clinical scoring system was employed for each dog enrolled in the study based on thoracic radiography and cardiac ultrasound (CU) examinations performed at Day − 15 (before treatment) and at Day 180. Results Results from the present study suggest that the majority of dogs from all treatment groups became antigen negative, as evaluated at Day 270: 9/10 dogs (90.0%) from G1, 6/10 dogs (60.0%) from G2 and 8/10 dogs (80.0%) from G3. Improvement of radiographic alterations was observed in all treatment groups, and almost all dogs were cleared of pulmonary abnormalities by 6 months from the beginning of treatment (P = 0.000). Cardiac ultrasound examination showed a progressive improvement of cardiac function in a limited number of animals (4/30). Conclusions The combination of doxycycline and three different formulations of moxidectin leads to antigen-negative status in naturally infected dogs.

Emerging risk of Dirofilaria spp. infection in shelter dogs in southern Italy

“…This finding is not consistent with other studies ( 43 , 44 ), in which the proportion of antigen-positive dogs was higher than that of Knott-positive dogs. However, one study showed the same pattern with dogs resulted positive with the modified Knott test but negative with the antigen test ( 45 ). The disagreement between the modified Knott test and the antigen test in the present study could be due to the low concentration of free antigen available for detection by serological tests.…”

Diversity and geographic distribution of haplotypes of Dirofilaria immitis across European endemic countries

“…In total, 122 heartworm isolates from different hosts were analysed from nine endemic countries, in Europe (Portugal, Spain, Italy, Greece, Hungary, Romania, Slovakia and Ukraine) and a single isolate from Bangladesh (Table 1 ) [ 39 – 42 ]. A single isolate was collected from a dog from Portugal which travelled with its owners and was diagnosed with D. immitis upon its arrival to Poland; therefore, it is safe to assume that the dog was infected in Portugal.…”