SoutheaSt aSian J trop Med public health 756 Vol 48 No. 4 July 2017 Correspondence: Dr Supaluk Popruk, Depart- ment of Protozoology, Faculty of Tropical Medi- cine, Mahidol University, 420/6 Ratchawithi Road, Ratchathewi, Bangkok 10400, Thailand. Tel: +66 (0) 23549100-4; Fax: +66 (0) 2643 5601 E-mail: supaluk.pop@mahidol.ac.th ACTIVITY OF PLANT ESSENTIAL OILS AGAINST GIARDIA DUODENALIS Supaluk Popruk 1 , Kanthinich Thima 1 , Ruenruetai Udonsom 1 , Rachatawan Chiabchalard 1 , Aongart Mahittikorn 1 , Kaewmala Palukul 2 and Apanchanid Thepouypom 3 1 Department of Protozoology, 2 Department of Entomology, 3 Department of Tropical Nutrition and Food Science, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand Abstract. Giardia duodenalis (synonyms: Giardia lamblia and Giardia intestinalis) is a common fagellate, zoonotic protozoan causing the diarrheal disease giardiasis. There is little information about the essential oils of plants found in Thailand against this parasite. We aimed to determine the efcacy of essential oils of the following plants against G. duodenalis: Syzygium aromaticum, Zingiber ofcinale Roscoe, Alpinia galanga, Litsea cubeba, Illicium verum, Zanthoxylum rhetsa, Citrus × aurantifolia, Citrus hystrix, Citrus reticulata, Ocimum basilicum and Ocimum africa- num, using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay. It was found that essential oils of C. × aurantifolia was the most efective against G. duodenalis with IC 50 = 6.96 ± 0.13 µg/ml, followed by L. cubeba with IC 50 = 60.67 ± 0.82 µg/ml in dose-dependent fashion. The other essential oils had no efcacy against G. duodenalis, suggesting they may contain fewer antigiardial constituents. Future studies are needed to elucidate major active constituents of these essential oils and prove their efcacy and safety for treatment of G. duodenalis. Keywords: Giardia duodenalis, essential oils, dose-dependent fashion high prevalence of giardiasis among many children in developing countries (Kotlof et al, 2013). Giardiasis can cause greasy stools, flatulence, diarrhea, abdominal cramps, epigastric tenderness and malab- sorption (Ankarklev et al, 2010; Bartelt and Sartor, 2015). The incidence of giardiasis depends on age, sanitation and personal hygiene (Stuart et al, 2003). G. duodenalis consists of eight assemblages (A-H). Hu- man giardiasis is caused by assemblages A and B. Assemblages A and B have also been identifed in other animals (Ryan and Cacciò, 2013). This suggests other animals may act as reservoirs for G. duodenalis and may be linked to zoonotic transmission. INTRODUCTION Giardia duodenalis (synonyms: Giardia lamblia and Giardia intestinalis) is the most common fagellate protozoan infecting humans worldwide (Ramírez et al, 2015; Soares and Tasca 2016). Most infec- tions occur from fecal-oral transmission through ingestion of contaminated water or food (Soares and Tasca 2016). There is a