Efficacy and safety of selamectin against gastrointestinal nematodes in cats presented as veterinary patients

Modular polyketide synthase-derived insecticidal agents: from biosynthesis and metabolic engineering to combinatorial biosynthesis for their production

Covering: up to 2022Polyketides derived from actinomycetes are a valuable source of eco-friendly biochemical insecticides. The development of new insecticides is urgently required, as the number of insects resistant to more than one drug is rapidly increasing. Moreover, significant enhancement of the production of such biochemical insecticides is required for economical production. There has been considerable improvement in polyketide insecticidal agent production and development of new insecticides. However, most commercially important biochemical insecticides are synthesized by modular type I polyketide synthases (PKSs), and their structural complexities make chemical modification challenging. A detailed understanding of the biosynthetic mechanisms of potent polyketide insecticides and the structure-activity relationships of their analogs will provide insight into the comprehensive design of new insecticides with improved efficacies. Further metabolic engineering and combinatorial biosynthesis efforts, reinvigorated by synthetic biology, can eventually produce designed analogs in large quantities. This highlight reviews the biosynthesis of representative insecticides produced by modular type I PKSs, such as avermectin, spinosyn, and spectinabilin, and their insecticidal properties. Metabolic engineering and combinatorial biosynthetic strategies for the development of high-yield strains and analogs with insecticidal activities are emphasized, proposing a way to develop a next-generation insecticide.

Efficacy of single topical treatment of Selamectin (Revolution®) against Ancylostoma ceylanicum in experimentally infected cats

Ancylostoma ceylanicum, a species of hookworm, is a common parasite of dogs and cats in the Asia-Pacific region. The objective of this study was to determine the efficacy of a single topical treatment of selamectin (Revolution®) against A. ceylanicum in experimentally infected cats. 12 kittens were injected with 300 infective stage larvae (L3) of A. ceylanicum by the subcutaneous route. Faecal samples were examined daily (days 7-15) for the presence of hookworm eggs. On day 18 kittens were stratified by faecal egg count and randomly allocated in equal numbers to control (n = 6) and treatment (n = 6) groups. Faecal egg counts were then performed daily (days 14-27) or every 3 days (days 28-51) until the end of the study and compared between the treated and control groups. Kittens in the treatment group were administered a single topical dose of selamectin (Revolution®), per label recommendations (6 mg/kg), on day 19. Kittens in the control group were not treated. At 4 days post-treatment, no hookworm eggs were detected in the treated group. Faecal samples from this group remained negative throughout the study, the treatment efficacy was 100% egg reduction (P < .0001). Average faecal egg counts remained high (558 ± 231 eggs per gram) in the untreated control group until the end of the study period. In conclusion, a single topical treatment of selamectin (Revolution®) at the recommended dose was highly efficacious against infection with A. ceylanicum in cats.

Efficacy and safety of a new topical formulation containing selamectin and sarolaner in the prevention of heartworm disease and the treatment of roundworm infection in cats presented as veterinary patients in Japan

The efficacy and safety of a new topical formulation containing selamectin plus sarolaner (Revolution® Plus / Stronghold® Plus, Zoetis) was evaluated for the prevention of heartworm (Dirofilaria immitis) disease and the treatment of roundworm infection in cats enrolled as veterinary patients in two field studies conducted in Japan. In the heartworm field study, 91 cats negative for D. immitis antigen and anti-D. immitis antibody were enrolled and received 9 monthly topical treatments with selamectin plus sarolaner during the period of April to December 2015. Efficacy was assessed by testing post-treatment blood samples collected 8, 12, and 15 months after initiation of treatment for the presence of D. immitis antigen and anti-D. immitis antibody. Eighty-seven cats completed the entire study and were included in the determination of efficacy. No D. immitis antigen or anti-D. immitis antibody were detected in any of the post-treatment samples. In the roundworm field study, completed in the period from April to November 2015, 64 cats with ≥100 roundworm eggs per gram (EPG) of feces were enrolled and allocated randomly in a 1:1 ratio, to receive either selamectin plus sarolaner or emodepside plus praziquantel (Profender®, Bayer). Treatments were administered topically on Days 0 and 30, and efficacy was assessed by fecal EPG counts conducted on Days 14, 30, and 60. All cats completed the entire study. At enrollment, all cats were infected with Toxocara cati. Compared to pre-treatment, geometric mean T. cati EPG counts on Days 14, 30, and 60 were reduced by >99.9% in both treatment groups. There were no treatment-related adverse events in either study. Monthly topical administration of Revolution® Plus / Stronghold® Plus providing a minimum of 6 mg/kg selamectin and 1 mg/kg sarolaner was safe and effective in the prevention of heartworm disease and the treatment of roundworm infection in cats enrolled as veterinary patients in Japan.

Efficacy and safety of a new topical formulation of selamectin plus sarolaner in the treatment and control of natural infections of Ancylostoma tubaeforme and Toxocara cati in cats presented as veterinary patients in the United States

A new topical formulation of selamectin plus sarolaner (Revolution^® Plus/Stronghold^® Plus, Zoetis) was evaluated in the treatment and control of naturally occurring infections of Ancylostoma tubaeforme and Toxocara cati in cats presented as veterinary patients in the United States. Three thousand three hundred three (3303) cats were screened in 25 veterinary practices in 15 states and 153 hookworm-positive cats (A. tubaeforme and/or A. braziliense), mainly from Alabama, Mississippi, Texas, and Hawaii, were identified; 135 cats met all the criteria for enrollment and were included on study. The cats were randomly assigned to treatment with Revolution^® (at the label dosage, to provide a minimum dosage of 6 mg/kg selamectin) or selamectin plus sarolaner (at a dosage of 6-12 mg/kg plus 1-2 mg/kg, respectively). Treatments were administered at the time of enrollment and repeated 30 days later. Fecal samples were collected for differential fecal egg count prior to the first treatment (Day 0), prior to the second treatment (Day 30), and approximately 30 days later (Day 60). Efficacy was based on the percentage reductions in geometric mean fecal egg count for A. tubaeforme on Day 30 and Day 60 compared with Day 0. Where cats were co-infected with T. cati, efficacy against this species was also evaluated. Efficacy data were evaluated for A. tubaeforme for 40 cats on both Day 30 and Day 60 for the group treated with the selamectin/sarolaner combination and reductions in geometric mean fecal egg counts of 99.4% and 99.7% were demonstrated for Day 30 and Day 60, respectively. For the group treated with selamectin alone, 44 and 40 cats were evaluated and percent reductions for Day 30 and Day 60 were 99.5% and 99.9%, respectively. For T. cati, 14 cats were evaluated in the selamectin/sarolaner-treated group for Day 30 and for Day 60, and the reduction in geometric mean fecal egg count was 100% for both days. There were 11 and 9 cats evaluated for Day 30 and Day 60, respectively, for the selamectin-treated group and the reduction was again 100% for both days. The geometric mean fecal egg counts post-treatment were significantly lower than pre-treatment for both A. tubaeforme and T. cati, for both treatments, and for both periods of interest (P < 0.0001). No serious adverse events related to treatment with either product occurred during the study. Thus, both selamectin alone and the combination product of selamectin/sarolaner were safe and effective when administered on a monthly basis for the treatment and control of natural infections of A. tubaeforme and T. cati. The addition of sarolaner to the formulation did not interfere with the efficacy of selamectin against these nematodes.

Efficacy of a new spot-on formulation of selamectin plus sarolaner for cats against adult Ctenocephalides felis, flea egg production and adult flea emergence

A new spot-on formulation of selamectin plus sarolaner was evaluated against fleas for adulticidal efficacy, and for the effect on egg production and hatching when applied to flea-infested cats. Ten male and ten female adult domestic shorthair cats were randomly assigned to one of two treatment groups based on pre-treatment flea counts. Cats received topical treatment on Day 0 in a single spot to the dorsal scapular area with either a placebo formulation or with the combination formulation at the minimal dose of 6.0mg selamectin plus 1.0mg sarolaner per kg bodyweight. On Days -1, 5, 12, 19, 26 and 33, cats were infested with approximately 100 (±5) unfed Ctenocephalides felis fleas. At 24h after treatment or 48h after subsequent flea infestation, cats were housed for a 20-h period in a cage to allow collection of flea eggs. At the end of this period, flea eggs were collected from the cages and cats were combed to remove and count live fleas. Emerged viable larvae and emerged adult fleas were counted 3days and 35days, respectively, after egg collection. The new spot-on formulation of selamectin plus sarolaner provided 100% efficacy against adult fleas up to Day 36 following a single application. Fleas on placebo-treated cats produced large numbers of eggs throughout the study, with individual counts ranging from 110 to 1256 eggs. Following treatment, four flea eggs were collected from a single selamectin/sarolaner-treated cat on Day 29, but there were no eggs collected from any other selamectin/sarolaner-treated animal during the study. No larvae or adult fleas developed from these four eggs. From the eggs collected from the placebo-treated cats, the mean percentage of live larvae and adults that emerged ranged from 67.3% to 84.2% and from 50.7% to 81.8%, respectively. A single topical treatment with a new spot-on formulation of selamectin plus sarolaner at the minimum label dose thus controlled fleas on cats and was 100% effective in preventing flea reproduction for over one month after treatment.

Pet roundworms and hookworms: a continuing need for global worming

Ascarids and ancylostomatids are the most important parasites affecting dogs and cats worldwide, in terms of diffusion and risk for animal and human health. Different misconceptions have led the general public and pet owners to minimize the importance of these intestinal worms. A low grade of interest is also registered among veterinary professions, although there is a significant merit in keeping our guard up against these parasites. This article reviews current knowledge of ascarids and ancylostomatids, with a special focus on pathogenicity, epidemiology and control methods in veterinary and human medicine.

Macrocyclic Lactone Endectocides

The macrocyclic lactone endectocides such as ivermectin, abamectin, selamectin and moxidectin have revolutionized the treatment of parasitic diseases in animals, being active against internal and external parasites. Ivermectin was introduced into veterinary medicine in the 1980s and since that time a number of related compounds have been introduced. In the treatment of internal parasites they complement the use of levamisole and the benzimidazoles, but in recent years they have found utility in treating external insect parasites. These agents show very low levels of toxicity under most circumstances. However, they are neurotoxic particularly in subpopulations of animals with mutations in the MDR1 gene. Toxicity may be also seen during off-label use, possibly because the doses used have been extrapolated from use in other animals. Regardless of these considerations, the macrocyclic lactone endectocides are extremely effective and safe drugs in the treatment of parasitic diseases of animals.

Comparison of efficacy of selamectin, ivermectin and mebendazole for the control of gastrointestinal nematodes in rhesus macaques, China

An experiment was conducted to evaluate the efficacy of ivermectin and mebendazole compared with selamectin against gastrointestinal nematodes in rhesus macaques. A total of 60 rhesus macaques (Macaca mulatta), which were all infected with gastrointestinal nematodes, were randomly assigned to three treatment groups (selamectin, ivermectin and mebendazole) and one control group. Fecal samples for determining nematode egg counts were collected pre- and post-treatment. All treatments resulted in decrease in the number of eggs per gram (EPG) in the post-treatment sample compared with the pre-treatment sample. Reductions of mean egg counts from day -3 levels were 99.4% for selamectin, 99.2% for ivermectin and 99.4% for mebendazole on trial day 11, respectively. However, no significant difference was found among treatment groups. According to the data demonstrating a similar efficacy in selamectin-, ivermectin- and mebendazole-treated rhesus macaques, it was effective and convenient to apply either selamectin and ivermectin or mebendazole in rotation on the local conditions.

Efficacy of milbemycin oxime against fourth-stage larvae and adults of Ancylostoma tubaeforme in experimentally infected cats

The efficacy of milbemycin oxime against fourth-stage (L4) larvae and adults of Ancylostoma tubaeforme was investigated in a trial involving 24 young domestic shorthair cats. The animals were inoculated with approximately 300 infective stage three (L3) larvae and divided into three groups. After 12 days, eight cats (group 1) were treated with medicated tablets containing 4 mg milbemycin and 10 mg praziquantel to test the efficacy against L4 larvae; eight cats in group 2 were treated with the same tablets after 33 days to test the efficacy against adult worms; and eight cats in group 3 were treated with a placebo tablet. Faecal egg counts were determined periodically in each cat and after 40 or 41 days the number of worms in each animal was determined postmortem. The egg count reduction was determined by comparing the geometric mean numbers of eggs per gram of faeces in the placebo and medicated groups, and the worm reduction by comparing the geometric mean numbers of worms. The egg count reduction was more than 99 per cent in both treated groups, while the number of worms in groups 1 and 2 were reduced by 94.7 per cent and 99.2 per cent, respectively.

Safety of selamectin in cats

The safety of the avermectin, selamectin, was evaluated for topical use on the skin of cats of age six weeks and above, including reproducing cats and cats infected with adult heartworms. All studies used healthy cats. Acute safety was evaluated in domestic cross-bred cats. Margin of safety was evaluated in domestic-shorthaired cats, starting at six weeks of age. Reproductive, heartworm-infected, and oral safety studies were conducted in adult, domestic-shorthaired cats. Studies were designed to measure the safety of selamectin at the recommended dosage range of 6-12mgkg(-1) of body weight. Assessments included clinical, biochemical, pathologic, and reproductive indices. Selected variables in the margin of safety study and the reproductive studies were subjected to statistical analyses by using a mixed linear model. Cats received large doses of selamectin at the beginning of the margin of safety study when they were six weeks of age and at their lowest body weight, yet displayed no clinical or pathologic evidence of toxicosis. Similarly, selamectin had no adverse effect on reproduction in adult male and female cats. There were no adverse effects in heartworm-infected cats. Oral administration of the topical formulation, which might occur accidentally, caused mild, intermittent, self-limiting salivation and vomiting. Selamectin is a broad-spectrum avermectin endectocide that is safe for use in cats starting at six weeks of age, including heartworm-infected cats and cats of reproducing age, when administered topically to the skin monthly at the recommended dosage to deliver at least 6mgkg(-1).

Efficacy of selamectin against experimentally induced and naturally acquired infections of Toxocara cati and Ancylostoma tubaeforme in cats

The efficacy of selamectin against experimentally induced and naturally acquired infections of adult ascarids (Toxocara cati) and adult hookworms (Ancylostoma tubaeforme) was evaluated in five controlled studies in cats. Two studies evaluated the efficacy of selamectin against both ascarid (natural or induced) and hookworm (induced) infections; two studies evaluated the efficacy of selamectin against single natural infections of T. cati or A. tubaeforme; and the fifth study evaluated the efficacy of selamectin against induced infections of A. tubaeforme. Cats received selamectin topically in unit doses designed to deliver a minimum of 6mgkg(-1). Treatments were applied to the skin on each animal's back at the base of the neck in front of the scapulae. For experimentally induced infections, cats were inoculated orally with approximately 500 embryonated eggs of T. cati 56 days prior to treatment and/or approximately 150-250 larvae (L(3)) of A. tubaeforme 30 or 42 days prior to treatment. For both induced and naturally acquired infections, cats were allocated randomly to treatments (6-12 cats per treatment) on the basis of fecal egg counts to receive either selamectin or a vehicle containing the inert formulation ingredients. In all studies, adult worm counts were performed at necropsy 14 days after the last treatment administration. Against T. cati, a single application of selamectin provided a 100% reduction in the geometric mean number of adult worms for both experimentally induced and naturally acquired infections. Against A. tubaeforme, a single administration of selamectin provided a 99.4% reduction in the geometric mean number of adult worms in cats with natural infections, and an 84.7-99.7% reduction in adult worms in cats with induced infections. Two doses of selamectin administered at monthly intervals provided a 91.9% reduction in the geometric mean number of adult A. tubaeforme worms in cats with experimentally induced infections. The geometric mean numbers of adult worms (T. cati and A. tubaeforme) from selamectin-treated cats were significantly (P< or =0.0018) lower than for vehicle-treated cats in all studies. Thus, a single topical unit dosage providing a minimum dosage of 6mgkg(-1) selamectin was highly effective in the treatment of naturally acquired and experimentally induced infections of T. cati and A. tubaeforme in cats.