The efficacy of a selamectin (Stronghold®) spot on treatment in the prevention of Bartonella henselae transmission by Ctenocephalides felis in cats, using a new high-challenge model

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Abstract
Bartonella henselae is the causative agent of cat scratch disease in humans, which is recognized as an emerging zoonotic disease. Ctenocephalides felis is the main vector, and transmission of B. henselae infection between cats and humans occurs mainly through infected flea feces. Control of feline infestation with this arthropod vector therefore provides an important strategy for the prevention of infection of both humans and cats. In the present study, a new challenge model is used to evaluate the efficacy of selamectin (Stronghold® spot on) in the prevention of B. henselae transmission by C. felis. In this new challenge model, domestic cats were infected by direct application of B. henselae-positive fleas. The fleas used for infestation were infected by feeding on blood that contained in vitro-cultured B. henselae. The direct application of the fleas to the animals and the use of different B. henselae strains ensured a high and consistent challenge. Two groups of six cats were randomly allocated on pre-treatment flea counts to either control (untreated cats) or the selamectin-treated group with one pipette per cat according to the label instruction. Stronghold (selamectin 6 % spot on solution) was administered on days 0 and 32. On days 3, 10, 19, 25, and 31, each cat was infested by direct application of 20 fleas that fed on blood inoculated with B. henselae. Polymerase chain reaction (PCR) on pooled fleas confirmed that the fleas were infected. Blood samples were collected from each cat on days −3 (prior to flea infestation and treatment), 9, 17, 24, 30, 37, and 44 and assayed for B. henselae antibodies using an indirect immunofluorescence (IFA), for the presence of bacteria by bacterial culture and for B. henselae DNA presence by PCR. Cats were also assessed on a daily basis for general health. There were no abnormal health observations during the study and none of the animals required concomitant treatment. None of the cats displayed any clinical signs of bartonellosis during the study. In the untreated group, all cats became bacteremic within 17 to 44 days. None of the selamectin-treated cats became positive during the study. It was concluded that Stronghold® spot on administered to cats was efficacious in the prevention of the transmission of B. henselae by fleas to cats in a high-challenge model.

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