Development and characterization of ivermectin nanoformulations for topical acaricidal activity against Rhipicephalus sanguineus ticks

Ticks are among the most significant ectoparasites of livestock and humans, posing serious health and economic risks. The growing resistance to conventional acaricides highlights the need for safer and more effective alternatives. This study aimed to evaluate the acaricidal efficacy of different ivermectin (IVM) nanoformulations against different developmental stages of Rhipicephalus sanguineus tick. Different ivermectin nanoformulations were fabricated and evaluated for their physicochemical properties. An in vitro study was performed using larval, nymphal, and adult immersion tests, followed by an in vivo trial against unfed adults using the most effective formulation. All nanoformulations showed particle sizes from 450 to 650 nm and a polydispersity index range from 0.34 to 0.65. IVM spanlastics exhibited the smallest particle size, highest encapsulation efficiency (92%), and a sustained release profile. Based on LC₅₀ values, IVM spanlastics showed superior acaricidal activity against larvae (LC₅₀: 0.05%), nymphs (LC₅₀: 0.09%), and unfed adults (LC₅₀:0.16%); followed by IVM-SeNPs, where the LC₅₀ values were 0.10, 0.23, and 0.38% for larvae, nymphs, and unfed adults, respectively. The in vivo study of IVM spanlastics demonstrated 100% mortality of adult ticks within four days after application. IVM spanlastics could be topically applied as an alternative to conventional injectable IVM to control R. sanguineus ticks. Further toxicological studies are necessary to ensure the safety of these formulations for environmental and veterinary use.