Therapeutic and protective efficacy of doramectin injectable against gastrointestinal nematodes in cattle in New Zealand: a comparison with moxidectin and ivermectin pour-on formulations

*Inactivation of encysted muscle larvae of Trichinella spiralis in pigs using Mebendazole

We evaluated the effect of 4 anthelmintic treatments on the viability of Trichinella spiralis encysted muscle larvae (ML) 55 days post infection (PI) in experimentally infected pigs. Muscle larvae were isolated from pig muscle by artificial digestion after oral treatment of pigs with Levamisole (8 mg/kg, daily for 5 days) and Mebendazole (50 mg/kg, daily for 5 days); Doramectin (0.3 mg/kg, single IM injection), and Moxidectin (0.5 mg/kg, single pour on). Isolated larvae from treated pigs were orally inoculated into mice to assess viability of ML from each treatment. Only Mebendazole treatment of pigs significantly reduced ML viability in mice. The effect of timing of the effective Mebendazole treatment on ML from a longer term infection was then examined in a second experiment. Analysis revealed that Mebendazole treatment of pigs with 250 mg/kg over 3 days (83 mg/kg/day) or 5 days (50 mg/kg/day) reduced numbers of ML recovered from pig tissues compared to untreated, infected controls, and rendered ML non-infective to mice; Mebendazole treatment of pigs with 250 mg/kg in a single dose was not effective in reducing ML numbers recovered from pigs or in impacting ML infectivity to mice. An examination of the lowest effective dose of Mebendazole on encysted ML was determined in a third experiment. Mebendazole of pigs with 5, 50, or 100 mg/kg over 3 days demonstrated that 5 or 50 mg/kg over 3 days insufficient to reduce infectivity in recovered ML, while 100 mg/kg (and 83 g from experiment 2) over 3 days significantly reduces infectivity of ML. This procedure provides a means to evaluate the efficacy of various anthelmintic treatments on the viability of Trichinella spiralis ML in pig tissues, and identified Mebendazole, at 83-100 mg/kg administered over a 3-5 day period as an anthelmintic which renders encysted Trichinella spiralis ML from pig tissues non-infective. As risk from Trichinella significantly impacts acceptance of pork from pasture-raised pigs, these data provide a method, especially for producers of these high-risk pigs, to eliminate the potential of Trichinella transmission from infected pork.

Characterization of Moxidectin against Strongyloides ratti: In Vitro and In Vivo Activity and Pharmacokinetics in the Rat Model

Strongyloides stercoralis is a soil-transmitted helminth affecting an estimated 30-100 million people. Since the infection may be severe and life-threatening, accessible and effective treatment is pivotal. Currently, ivermectin is the drug of choice but has limitations. Moxidectin, a veterinary anthelminthic approved for use in human onchocerciasis, is a promising drug alternative against strongyloidiasis. In this study, we evaluated the in vitro activity of moxidectin on Strongyloides ratti larvae (L₃) and adult females and the activity as well as the pharmacokinetics of moxidectin in S. ratti infected rats. In vitro, moxidectin had an activity that was similar to that of ivermectin, with median lethal concentration values for L₃ and adults in the range of 0.08-1.44 μM, after 72 h of exposure. In vivo, doses of 250, 500, and 750 μg/kg of moxidectin resulted in a reduction of the worm burden ranging from 48.5 to 75%. At the highest dose (750 μg/kg) we observed a maximal blood concentration of 50.3 ng/mL and an area under the curve of 895.2 ng × h/mL. The half-life in rats was 9 h, and moxidectin was cleared to undetectable blood levels within 7 d (<10 ng/mL). No exposure-response relationship was observed. This work contributes to the characterization of moxidectin in the treatment of S. ratti as a model of Strongyloides spp. and, as such, supports moving moxidectin further along the drug development pipeline in the treatment of human strongyloidiasis.

Endectocide activity of a pour-on formulation containing 1.5 per cent ivermectin +0.5 per cent abamectin in cattle

The present work aimed to evaluate, through ten different studies, the therapeutic efficacy of a new pour-on formulation, containing 1.5 per cent ivermectin +0.5 per cent abamectin, against parasites of cattle. Results obtained on trials against Rhipicephalus (Boophilus) microplus showed that the pour-on combination of 1.5 per cent ivermectin +0.5 per cent abamectin obtained superior efficacy indexes against this ectoparasite, when compared with formulations containing 0.5 per cent ivermectin, 1 per cent ivermectin and the combination of 1 per cent abamectin +20 per cent levamisole. The results of efficacy of the ivermectin+abamectin and the 0.5 per cent ivermectin against Haematobia irritans were similar. Against Cochliomyia hominivorax larvae, all pour-on formulations tested (1.5 per cent ivermectin +0.5 per cent abamectin, 0.5 per cent ivermectin and 0.5 per cent abamectin), as well as 1 per cent doramectin administered subcutaneously, were considered ineffective. Cattle medicated with 1.5 per cent ivermectin +0.5 per cent abamectin, pour-on, remained free from parasitism by Dermatobia hominis larvae during 42 days (96 per cent efficacy), while values superior to 90 per cent were obtained by 0.5 per cent ivermectin (92 per cent) and 0.5 per cent abamectin (93 per cent) until the 42nd and 35th days post treatment, respectively. Against Haemonchus placei and Oesophagostomum radiatum, the pour-on of ivermectin+abamectin showed better efficacy than the 0.5 per cent ivermectin and 0.5 per cent abamectin. As to Cooperia punctata, there was no difference regarding efficacy results obtained by the avermectins combination and abamectin. The pour-on combination of 1.5 per cent ivermectin +0.5 per cent abamectin obtained high efficacy against R. (B.) microplus, D. hominis and some species of cattle gastrointestinal helminths when compared with formulations of 0.5 per cent ivermectin and 0.5 per cent abamectin administered through the same route.

Treatment of external and internal parasites of cattle

To control parasitic disease in cattle, one first has to determine what parasites he or she is trying to control--nuisance and biting flies in a milking parlor or ticks on range cattle? The determination may be based on geographic location, class of cattle, and their management. After determining what is there, then if the numbers are sufficient, justify treatment. Each livestock producer has a different array of parasites with which to deal, and in some circumstances, parasitic disease is below the economic threshold. Others may have occasional clinical disease associated with parasites, but most have situations in which the potential of economic loss is high enough to justify control.