Evaluation of anthelmintic activity of biologically synthesized silver nanoparticles against the gastrointestinal nematode, Haemonchus contortus R.S. Tomar and S. Preet* Department of Zoology, Faculty of Science, Dayalbagh Educational Institute, Dayalbagh, Agra-282005, India (Received 16 December 2015; Accepted 1 June 2016) Abstract The present study focuses on the in vitro anthelmintic activity of silver nanoparticles (AgNPs) synthesized using the aqueous extract of Azadirachta indi- ca against Haemonchus contortus. The synthesized AgNPs were characterized by ultraviolet–visible (UV-Vis) spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies. The UV-Vis spectrum exhibited a sharp peak at 420nm, which was vali- dated by electron microscopy, indicating the preparation of spherical nanoparticles measuring 15–25 nm in size. The in vitro study was based on an egg hatch assay (EHA) and adult motility inhibition assays. Six concentrations of AgNPs were used for EHA, ranging from 0.00001 to 1.0 μg/ml, and a range of 1–25 μg/ml was used for adult worms. The highest concentration induced 85 ± 2.89% egg hatch inhibition. The IC 50 value for EHA was 0.001 μg/ml, whereas in vitro adult H. con- tortus motility inhibition was produced at 7.89 μg/ml (LC 50 ). The effectiveness of A. indica leaf extract (aqueous) was also evaluated, which showed an IC 50 value for EHA of 115.67 μg/ml, while the LC 50 against adult H. contortus was 588.54 μg/ml. The overall findings of the present study show that the experimental plant extract contains reducing properties for the synthesis of AgNPs which, in turn, showed potent anthelmintic properties. This is the first report where AgNPs have been tested for their anthelmintic properties in an in vitro model. Introduction Helminthiasis represents a major constraint to the de- velopment of livestock production as it is responsible for great economic losses, particularly in the regions where extensive grazing is practised (Waller, 1997). Increased mortality, decreased meat production and reproductive fitness result from severe gastrointestinal nematode infec- tion in ruminants (Hoste et al., 2005). In order to overcome the deleterious effects of helminths, conventional chemical anthelmintics are the first choice; however, the livestock production industry does not benefit through these con- trol measures, due to higher cost and the non-availability of such compounds to small farmers. Moreover, these parasites have evolved resistance to various anthelmin- tics, such as benzimidazole, imidazothiazole and ivermec- tin, which has become a major problem worldwide (Singh et al., 2002; Waller, 2003), making their management more difficult. The use of traditional botanicals has emerged as an environmentally safer alternative, proving successful against these parasites (Eguale et al., 2007a; Kamaraj et al., 2011; Kanojiya et al., 2015). Haemonchus contortus, a predominant gastrointestinal nematode in the small ruminants of the tropical, sub- tropical and temperate countries, has been a targeted pathogen due to its rigorous damage to sheep and *Fax: +91-0562-2801226 E-mail: preetshabd@gmail.com Journal of Helminthology, Page 1 of 8 doi:10.1017/S0022149X16000444 © Cambridge University Press 2016