Giardia lamblia is one of the most frequent protozoan parasites that cause giardiasis worldwide. According to WHO reports annually 280 million people have been infected globally (Carter et al., 2018). Giardiasis is becoming an increasingly prevalent issue, particularly in developing country, as it continues to emerge and spread within human populations. In developed countries, the prevalence rate of giardiasis is between 2-5%, while in developing countries ranges from 20-30% (Lalle et al., 2018). The disease is typically transmitted indirectly through the consumption of food or water that has been contaminated with cysts or through person-to-person contact, especially among individuals living in unhygienic conditions. Although giardiasis can affect individuals of all ages and display symptoms, it tends to affect children more frequently than adults (Belkessa et al., 2021). Giardiasis can either be asymptomatic or result in symptoms such as diarrhoea, vomiting, flatulence, anorexia, and crampy abdominal pain during its acute phase (Escobedo et al., 2018). In addition to gastrointestinal symptoms, it may also lead to extra-intestinal manifestations such as fever, maculopapular rash, pulmonary infiltrate, lymphadenopathy, polyarthritis, urticaria and growth retardation. Metronidazole is considered the first-line treatment for giardiasis, but alternative medications like albendazole, furazolidone and tinidazole are also used (Beer et al., 2017). Adverse effects of common drugs results headaches, dizziness, metallic taste, low efficacy and treatment failure have been reported as potential issues that cannot be overlooked (Starrs and Yenigun, 2021). The development of resistance to chemotherapeutic drugs among parasites underscores the critical importance of exploring alternative therapeutic approaches. One such approach involves investigating natural plant products as potential novel anti-parasitic agents (Anthony et al., 2005).

Andrographis paniculata (Burm. F.) Nees, a member of the Acanthaceae family, is a plant that is commonly found in several Asian countries including China, India, Thailand, and Sri Lanka (Hossain et al., 2014). It has a long history of medicinal use in both Indian and Oriental medicine. Ancient Ayurvedic texts have highlighted its potential as an herb for addressing neoplasms and have documented at least 26 Ayurvedic formulations that incorporate it in the treatment of liver disorders (Okhuarobo et al., 2014). The plant, commonly referred to as the "king of bitters," is widely recognized for its highly bitter characteristics and has been traditionally employed as a treatment for various ailments, including the common fever, cold, dysentery, tonsillitis, liver ailments, diarrhoea, inflammation, herpes, and many others (Hossain et al., 2014). The plant contains various active compounds, such as diterpene lactones, flavonoids, and polyphenols, as reported in studies (Okhuarobo et al., 2014). Andrographolide (ADG), a diterpenoid lactone with the chemical formula C20H30O5, serves as the primary compound responsible for the plant's therapeutic properties (Chao and Lin., 2010). It is primarily concentrated in the leaves of the plant and can be readily isolated from plant crude extracts as a crystalline solid (Varma et al., 2011). ADG demonstrates an extremely broad spectrum of biological activities. Recent reports suggest that it possesses anti-tumour, cardio-protective, anti-HIV, antioxidant, anti-inflammatory, immunomodulatory, antibacterial, cytotoxic, neuroprotective, and hepatoprotective properties (Li et al., 2022). Furthermore, it has been shown to exhibit antimicrobial activity against bacteria and viruses.

This study underscores the effectiveness of andrographolide against giardiasis. Our research demonstrates its ability to induce cytotoxic effects, morphological changes, ROS production, DNA damage and cell cycle arrest in trophozoites. These results highlight potent anti-giardial properties of andrographolide, suggesting its potential for novel drug therapies for giardiasis.