The changing faces of parasite control
Carmel Taylor (Hong Kong) gave a brief introduction to the session, pointing out that the session was to be recorded, and acknowledged the support of the sponsor for the session, Merck Animal Health. She mentioned that two new antiparasitical products, Seresto® from Bayer (flumethrin + imidacloprid) and Activyl® (indoxacarb), a proinsecticide by Merck, would be included in the discussions. Carmel Taylor introduced the five discussion topics for the workshop and their contributors.
The use of permethrin spot-on formulations in dogs (M. Kietzmann)
Manfred Kietzmann (Germany) introduced a study he had performed in collaboration with parasitologists evaluating the distribution of permethrin in spot-on formulations and flumethrin incorporated in a collar (Seresto®) over the body surface of dogs, the effects of excipients, and the duration of antiparasitic (repellent) effects. He gave a short introduction on the structure and function of the epidermis. He discussed the three excipients in highly concentrated permethrin formulations: isopropyl myristate, N-methylpyrrolidone and propylene glycol with or without methyl ether. An in vitro study1 demonstrated diffusion of permethrin into the deeper layers of the skin, but no significant systemic absorption in dogs (in contrast to cats). Another in vivo, cross-over study2 in beagle dogs looked at the distribution on the body surface, persistence on the skin and the efficacy against Dermacentor reticulatus ticks. In this study, ticks were placed on the dorsal back, close to the treatment area, and on the legs, a site distant from the treatment area. Test formulations were Exspot® (Virbac: permethrin), Preventic® (Virbac: permethrin), Fletic® (permethrin) and Advantix® (Bayer Animal Health: permethrin + imidacloprid). At day 1 all ticks died, and after 2 and 3 weeks, in the face of further infestation, only a few ticks were attached on the legs and backs of the dogs, showing that the permethrin maintained some effectiveness over a 2–3-week period. No significant differences in distribution and efficacy were found between the different products/formulations. Permethrin was distributed rapidly (within 24 hours) over the whole body surface. This distribution was not via the hairs (concentrations in hair are high near treatment area and low at distant sites), but possibly via the horny layer (tape stripping showed a decline in concentration within the stratum corneum over time). This demonstrated the importance of the stratum corneum for the distribution over the body surface. Manfred Kietzmann commented that Seresto® collar from Bayer takes more than 1 day to release its compound flumethrin. He cited preliminary results of another study being performed by a colleague that demonstrated a significantly longer duration of action of the flumethrin (study in progress, currently exceeding 5 months).
Gila Zur (Israel) asked about general recommendations for use of flea control products on seborrhoeic dogs with a higher epidermal turnover rate and also for dogs with severe flea allergy.
Manfred Kietzmann replied that the advantage of the permethrin formulations is the repellent effect. In actual parasitoses drugs with immediate onset of action would be needed and, thereafter, permethrin-containing spotons or collars could be utilized. He had no data regarding effects of seborrhoea.
Amit Ranjan (Canada) asked about the onset of action after application of the Seresto® collar.
Manfred Kietzmann answered that the study found an onset of activity 1 day after application, but shorter periods were not studied. However, there are large variations between individuals. One important factor is the hair coat, as the drug is distributed via the lipophilic horny layer and then via the sebum on the hairs. Therefore, long-haired dogs need more of the compound to get the repellent effect than short-haired breeds.
Luisa Cornegliani (Italy) asked about the impact of shampoos used in atopic dogs on the length of action of antiparasitic products.
Manfred Kietzmann replied that more studies would be needed but that in his opinion the time of contact of shampoos with skin is relatively low; however, more frequent administration might be needed. He mentioned studies performed with benzoyl peroxide where no further parasiticide activity was observed after 2–4 weeks, and commented that the flumethrin collar is a good option for animals requiring frequent bathing.
Helena Vaynberg (USA) asked whether different recommendations should be made by manufacturers for use of parasiticides on long-haired dogs.
Manfred Kietzmann stated that there is limited information on distribution effects of insecticides in different hair coat types. Further studies would be needed.
The chairperson introduced Richard Malik as the next speaker.
Permethrin intoxication in cats (R. Malik)
Richard Malik (Australia) spoke about the pharmacology of permethrin and commented that it is not really known why permethrin is toxic for cats. He described the clinical signs of permethrin toxicity in cats. He pointed out that in many supermarkets, dog and cat ectoparasiticides are next to each other, that many permethrin-containing products have only small warning icons for cats, and there were often no further ‘warning icons’ once the packet was opened. He mentioned that additionally cat products are often more expensive and, therefore, cat owners might spuriously buy permethrin-containing dog products. He emphasized that no over-the-counter product prominently warns of secondary toxicity due to contact, which can occur through direct contact of cats with dogs, through grooming (licking) of the dog by the companion cat, or through shared brushes or combs. There are no indications of what is the safe period of time that cats should be kept separated from dogs following product application. He then spoke about published data from a survey of veterinarians performed in Australia.3