Efficacy of semi-annual therapy of an extended-release injectable moxidectin suspension and oral doxycycline in Dirofilaria immitis naturally infected dogs

"Slow kill" treatment reduces DNA damage in leukocytes of dogs naturally infected with Dirofilaria immitis

Parasitic diseases are considered to be a cause of oxidative stress which leads to oxidative damage of various molecules including DNA. This can result in mutations, replication errors, and genome instability. Therefore, aim of this study was to measure DNA damage induced by Dirofilaria immitis in the single cells such as dogs' leukocytes using the comet assay. Also, we monitored the effects of antiparasitic treatment on mitigation of sensitivity to DNA damage in leukocytes treated with H2O2 using the in vivo and ex vivo comet assay. The whole blood samples from 34 dogs from Serbia were used, both males and females, from one to 13 years old, both pure and mixed-breeds. A rapid immunochromatographic test (Antigen Rapid Heartworm Ag 2.0 Test Kit, Bionote, Minnesota, USA) was used for the detection of D. immitis antigens. The modified Knott's test and PCR were used in the aim of detecting D. immitis microfilariae in dogs' blood, and evaluating the number of circulating microfilariae during the treatment. The genotoxicity evaluation showed that D. immitis infection resulted in DNA damage in naturally infected dogs, with the highest DNA damage occurring in the group of dogs with severe clinical signs. Treatment with ivermectin and doxycycline decreased DNA damage in leukocytes of dogs in all groups, as the intensity of infection decreased due to applied therapy. Ex vivo comet assay results showed that leukocytes exhibited decreased sensitivity to H2O2-induced DNA damage during treatment. The results of the modified Knott's test and PCR in our study showed that treatment with ivermectin and doxycycline was successful in decreasing the average number of microfilariae during the time and at the end eliminating them from the dogs' blood.

Heartworm adulticide treatment: a tropical perspective

Dirofilaria immitis (the canine heartworm) is widespread in the tropics, with prevalence surpassing 30% in high-risk areas. In addition to the suitable climatic conditions that favour mosquito abundance and filarial larva development, there is low compliance with the recommended year-round use of preventives in these transmission hotspots. This represents a major concern, considering that melarsomine (first-line heartworm adulticide) is unavailable in several tropical countries, resulting in the so-called slow-kill protocol being the only available adulticide treatment option. In this article, the members of TroCCAP (Tropical Council for Companion Animal Parasites) review the current distribution of heartworm in the tropics and the availability of melarsomine, and discuss alternatives for the management of heartworm infections in dogs.

Safety of Simparica Trio® (sarolaner, pyrantel, moxidectin) in heartworm-infected dogs

BACKGROUND

Assessment of the safety of heartworm preventatives in dogs with pre-existing patent heartworm (Dirofilaria immitis) infections is necessary because rapid adult worm and microfilarial death can lead to severe clinical complications, including thromboembolism and anaphylactic shock in dogs. The aim of this study was to determine the clinical safety of Simparica Trio^® (sarolaner, pyrantel, moxidectin) in heartworm-infected dogs and the degree of microfilaricidal and adulticidal activity of three consecutive monthly treatments of Simparica Trio.

METHODS

Twenty-four laboratory Beagle dogs were implanted with 10 male and 10 female D. immitis (ZoeKY isolate), and once infection was patent, they were randomized equally among three groups to receive no treatment, 1× or 3× the maximum recommended label dose of Simparica Trio. Dogs in the treated groups received Simparica Trio on days 0, 28 and 56. In-life assessments included body weight, physical examinations, clinical observations, daily general health observations, a quantitative estimate of food consumption and blood collections for pharmacokinetic (PK) analysis, microfilariae (MF) counts and D. immitis antigen testing. At the end of the study the heart, lungs and pleural and peritoneal cavities were examined for adult D. immitis worms.

RESULTS

Simparica Trio was generally well tolerated. Emesis occurred at low frequency in all groups including control. Abnormal stool occurred occasionally in the 1× and 3× groups throughout the 3-month study. Fever (> 104 °F/40 °C) was recorded in one 1× and one 3× dog 1 day after the first dose and resolved by the following day. No severe hypersensitivity reactions occurred. The mean number of circulating microfilariae (MF) counts in the control group increased from 12,000/ml at study start (Day 0) to > 20,000/ml at Day 28 and remained > 20,000/ml for the duration of the study. The least squares means of circulating MF were reduced by 69.8% on Day 1 and 97.4% on Day 7 for the 1× group and remained at > 99% lower than the control group for the remainder of the study. Similarly, least squares means of circulating MF were reduced by 85.3% on Day 1 and 93.9% on Day 7 for the 3× group and remained > 98% lower than the control group for the remainder of the study. At the end of the study, the mean number of implanted adult worms recovered was < 10 per sex in all groups with 90%, 85% and 75% of live adult heartworms recovered in control, 1× and 3× treatment groups, respectively. Low numbers of dead adult worms were recovered in 1× and 3×, with none in control. Following each dose, the moxidectin and sarolaner AUC and C_max had close to dose proportional increases.

CONCLUSIONS

This study demonstrated that Simparica Trio (sarolaner, pyrantel, moxidectin) was well tolerated when administered to heartworm-positive dogs at 1× and 3× the maximum recommended dose at 28-day intervals for 3 consecutive months. Simparica Trio significantly reduced microfilaria counts in both treatment groups, without significant clinical consequences. At the doses administered, Simparica Trio had minor adulticidal activity but resulted in no clinical sequelae.

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

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.

An Accessible Alternative to Melarsomine: "Moxi-Doxy" for Treatment of Adult Heartworm Infection in Dogs

Canine heartworm infection, caused by the filarial parasite Dirofilaria immitis, represents a serious and expanding animal welfare concern that is expected to increase due to the effects of climate change and the COVID-19 pandemic. A body of evidence has emerged to support the use of a non-arsenical adulticide treatment protocol, using moxidectin and doxycycline to kill adult heartworms over a prolonged period. While a three-dose protocol using the arsenical drug melarsomine is currently the safest and most effective treatment for heartworm infection, this drug is not available in some countries and is inaccessible for many owners and animal shelters. Moxidectin-doxycycline (moxi-doxy) provides a viable alternative to no treatment at all, in cases where arsenical treatment is not possible. Based on current evidence, the most effective non-arsenical treatment regimen is doxycycline 10 mg/kg PO q 12 or 24 h for 28 days, combined with topical moxidectin at label dose. Moxidectin is repeated monthly until no antigen detected (NAD) status is confirmed. Sustained release injectable moxidectin, in combination with doxycycline, may provide an alternative in remote regions or in settings where significant compliance or accessibility concerns exist, but more studies are needed. In moxi-doxy protocols, doxycycline should be repeated annually until NAD. This review summarizes the safety and efficacy of moxi-doxy, addresses controversies surrounding this treatment approach, and provides detailed recommendations for treatment regimens and post-treatment testing.