The knowns and unknowns of the efficacy of neem oil (Azadirachta indica) used as a preventative measure against Leishmania sand fly vectors (Phlebotomus genus)

Abstract

Since domestic dogs are the main reservoir hosts of Leishmania infantum throughout the world, they are the main focus in terms of controlling zoonotic visceral leishmaniosis. To protect dogs from leishmaniosis, chemical repellents of durable efficacy are available in the form of collars, spot-on and sprays. However, the negative effects of chemical pesticides on the environment are well established as they affect animals and plants. This phenomenon has created the need for safer and more environmentally friendly substitutes. Plant extract-based insecticides and/or repellents have therefore been increasingly used by pet owners and veterinarians. Several botanical products have been tested as insecticides and/or repellents against a variety of bloodsucking arthropods that transmit human diseases. Among the products tested against Leishmania vectors, neem oil containing azadirachtin is the most studied. This study reviews the scientific literature concerning the efficacy of neem oil (azadirachtin-based products) against phlebotomine sand fly bites. A questionnaire was also administered to assess Italian veterinarians’ attitudes to the use of neem oil. The survey was anonymous and consisted of three closed-ended questions.According to the data reported in the literature, the efficacy of neem oil in reducing the risk of sand fly bites has been tested against Phlebotomus papatasi, Phlebotomus perniciosus, Phlebotomus argentipes, Phlebotomus orientalis and Phlebotomus bergeroti. The efficacy of the products tested was expressed in percentages, ranging from 74.9% to 100%. The protection time was only available for six out of eight studies, ranging from “only during the first hour” (minimum protection time) to “all night” (expected maximum protection time). As regards the attitude to recommending the use of neem oil, 208 veterinarians participated in the online survey. Of the 126 veterinarians who recommended natural products, 119 (94.44%) reported that they recommended the use of neem oil-based products.Considering the limited data on the duration of protection and the dose of the active ingredient, more studies are required on the efficacy of neem oil-based products in reducing the risk of contracting canine leishmaniosis. These studies should also refer specifically to the concentration of the active ingredient as well as the interval of administration. Until such results are available, the use of azadirachtin-based products as the only topical products for the prevention of leishmaniosis in dogs is not recommended.