It seems that equine internal parasites aren’t the only ones becoming resistant to the products commonly used to treat them: The donkey chewing louse (Bovicola ocellatus) is developing resistance against pyrethroids, a common class of insecticide used against lice. The search for new lice treatments is on, and researchers from the United Kingdom believe that simple essential oil solutions could be one answer.

“Bovicola equi, the species of chewing louse found on horses, is very similar in appearance and behavior to the donkey chewing louse, B. ocellatus; in fact, the donkey chewing louse has not been thoroughly characterized and may be the same species,” explained Lauren Ellse, BSc, PhD, a research assistant at the University of Bristol, in England.

Ellse said chewing lice measure less than 2 mm in length, have a rounded head, and are light brown. These parasites can be found throughout the horse or donkey’s coat, where they feed on the sebum secretions at the base of the hair, she said.

“Chewing lice in equines are found worldwide and are often found in much higher numbers than sucking lice, which feed on the host’s blood,” she said. “They are often found in high numbers in animals which are already suffering from other illnesses, and they significantly compromise animal welfare. Therefore, controlling them is very important. However, growing levels of insecticide resistance in ectoparasites has made many conventional insecticides ineffective, and so alternative control measures are required