Sodium Alginate Nanoemulsions for the Delivery of <i>Eucalyptus staigeriana</i> Essential Oil: Production, Characterization, and Ovicidal and Larvicidal Effects against <i>Haemonchus contortus</i>

Eucalyptus staigeriana essential oil (EsEO) has well-known anthelmintic activity in small ruminants. However, its volatility limits its therapeutic action. The aim of this study was to develop a water-in-oil sodium alginate-based nanoemulsion with an effective in vitro effect on the eggs and larvae of Haemonchus contortus, a gastrointestinal parasite of sheep and goats. Four oil-in-water sodium alginate-based emulsions were prepared using a high-energy method with different proportions of Tween 80, EsEO, and sodium alginate (ALG) 4%. The physical-chemical characterization included stability, particle size, zeta potential and infrared spectra. The effects of the emulsions were evaluated against H. contortus via the egg hatching test (EHT) and larval development test (LDT). The results showed that the emulsions were stable over 7 days, nanometer scale particles (218.8 to 371.5 nm) predominating and with negative zeta potentials (−28.9 to −46.9 mV). All four emulsions were more effective than EsEO in the EHT, with 50% effective concentrations (EC50) of 0.088 to 0.15 mg/mL for the emulsions and 0.308 mg/mL for EsEO. However, in the LDT, the emulsions and essential oil had similar effects, with EC50 values of 3.91 to 4.60 mg/mL for the emulsions and 4.17 mg/mL for EsEO. Emulsion 2, with low Tween 80/EsEO and ALG/EsEO ratios, was considered better overall in terms of physical, chemical and anthelmintic assessment and is a promising candidate for further in vivo assays against adult H. contortus.