Background: Giardiasis is the most common infectious diseases of medical parasitology and public health in our country and in many countries is important. Accourding the importance of treating the disease, particularly parasite resistance to drugs. Thus, the aim of present study was investigated the effect of gold nanoparticles on Giardia lamblia cyst stage of the in vitro.

Materials and Methods: In this experimental study, Giardia cysts from contaminated fresh feces were collected and concentrated with use 0.85 M sucrose methods for isolation of cysts. Samples after counting with Noubar slide were stored at 4°C. The gold nanoparticles at concentrations of 0.05, 0.1, 0.3 mg/ml prepared and verified, the particle size was determined. The effect of different concentrations of the nanoparticles at 5, 15, 30, 60 and 180 minutes was evaluated and compared to control groups (metronidazole). Data from the study were recorded and analyzed with T-test and Chi-square by used SPSS software.

Results: The results of the cytotoxic effect of nanoparticles on the different concentration and time of Giardia lamblia cysts in vitro compared with the positive control (Metronidazole) shows mean percent of effect gold nanoparticles increased with increasing concentration and exposure time, so that the concentration of 0.3 mg/ml from 62% at 5 min to 96% at 180 min increased (p<0.05). Also, the survey results show Giardia cysts with increasing exposure time , killing effect of gold nanoparticles at a concentration of 78% in 0.05 mg/ml to 96% at a concentration of 0.3 mg/ml greatest increased (p<0.05). As a result, the concentration of gold nanoparticles in comparison with Metronidazole has the most effect gold nanoparticles at a concentration of 0.3 mg/mL, almost the same effect of Metronidazole as the drug of choice in the treatment of Giardia lamblia.

Conclusion: Therefore, the results of this study, gold nanoparticles at a concentration of 0.3 mg/ml as an effective combination for killing Giardia lamblia cysts in vitro can be used. Thus, future studies on laboratory animals (In vivo) are recommended.