Effect of oral administration of Bacillus thuringiensis var. oswaldocruzi to sheep on the development of larvae in fecal cultures

Haemonchus contortus is one of the most important gastrointestinal nematodes infecting sheep, being a production-limiting factor in sheep herds. Biological control has been used for many years either in combination with traditional parasiticides or as an alternative treatment itself. Bacillus thuringiensis can be a promising tool for an integrate control of H. contortus in sheep herds by disrupting nematode's life cycle, thus decontaminating pasture. This study aims to evaluate the larvicidal efficacy of Bacillus thuringiensis var. oswaldocruzi (Bto) on the development of H. contortus larvae in fecal sheep cultures. Bto concentrations (similar to(1010) colony forming units, CFU / mL) were orally administered to thirty-six ewes naturally infected with H. contortus in three different pharmaceutical forms: hard gelatin capsule, mucoadhesive gel or suspension. The different treatments were carried out in a single oral administration (SOA). All formulations were effective in inhibiting larvae development compared with control groups in all time points studied (p < 0.05). The mucoadhesive gel showed similar to 90% of efficacy on inhibiting larvae development during all the time points post SOA. The suspension had 85% efficacy on inhibiting larvae development at 24-48 h and 96% at 72-96 h. The hard gelatin capsule was 57%, 62%, 73% and 96% effective inhibiting larvae development at 24, 48, 72 and 96 h, respectively. This study highlights that disrupting the infective larval stage in the environment Bacillus thuringiensis var. oswaldocruzi is a promising prophylactic alternative in the H. contortus control.