Human cystic echinococcosis (CE) is a zoonotic disease caused by the larval stage of the parasite Echinococcus granulosus sensu lato (s.l.), which is responsible for serious health and economic problems. CE is distributed worldwide and is endemic in Peru, Chile, Argentina, Uruguay, Southern Brazil, the Mediterranean region, Central Asia, western China, and eastern Africa (Agudelo Higuita et al., 2016). The annual CE incidence ranges from <1 to 200 per 100,000, and the mortality rate is between 2% and 4%. Current estimates of the global burden average 285,500 disability-adjusted life years (DALYs). The World Health Organization (WHO) has listed echinococcosis as one of the 17 neglected diseases targeted for control or eradication by 2050 (Wen et al., 2019).

The parasitic cycle involves two hosts: a definitive host, usually dogs, and an intermediate host, mostly ungulates such as sheep, cows, pigs, and camels. Humans are accidental or “dead-end” hosts who acquire the disease after accidently ingesting the eggs shed in the feces of infected definitive hosts. When the eggs are ingested by an intermediate host, they can reach the venous circulation and eventually form cysts in the liver, lungs, or other organs (Eckert and Deplazes, 2004).

Currently available treatment options for CE based on the WHO-IWGE (World Health Organization Informal Working Group on Echinococcosis) classification of cyst stage include: i) surgery, ii) percutaneous treatment including the puncture, aspiration, injection, re-aspiration (PAIR) technique, iii) anti-parasitic treatment with albendazole (ABZ) and iv) observation with no intervention for inactive cysts (Siles-Lucas et al., 2018).

For human treatment, chemotherapy with ABZ, a derivative of benzimidazoles, is widely used as an alternative or adjuvant to PAIR or surgery, according to the site and stage of the cysts (Brunetti et al., 2010), and it is also the main option for inoperable cases. However, its reported efficacy is ∼50%, with an overall cure rate not exceeding 30%–48% (Moro and Schantz, 2009). Moreover, administration of ABZ in high doses or use of this drug for a long time may cause adverse side effects such as abnormalities in liver function, hepatotoxicity, alopecia, leucopenia, bone marrow suppression, encephalitis syndrome, influenza-like syndrome, and many other haematological disorders (Vuitton, 2009).

Currently, there is no alternative to ABZ as an antiinfective therapy for the treatment of echinococcosis, and thus novel compounds are urgently needed (Wen et al., 2019).

Medicinal plants have been used since ancient times for the treatment of human diseases, and over the past decades, have led to an increasing interest in the search for therapeutic approaches against infectious agents. They exhibit powerful pharmacological activities, are accessible, with relatively low cost, and have generally low toxicities (Hizem et al., 2019). The pharmaceutical properties of aromatic plants are partially attributed to essential oils (EOs) (Pessoa et al., 2002; Carson and Riley, 2003; Edris, 2007; Santoro et al., 2007; Tavares et al., 2008; Bakkali et al., 2008; Arana-Sánchez et al., 2010; Machado et al., 2010; Yuan et al., 2016; Ali et al., 2020; Soleimani et al., 2021). EOs are secondary metabolites that plants usually synthesize to combat infectious or parasitic agents or generate in response to stress conditions. EOs are aromatic components obtained from different plant parts such as flowers, buds, seeds, leaves, and fruits. Plant EOs are being studied extensively since they are known to possess numerous versatile properties such as antimicrobial, antibacterial, antiviral, antiparasitic, and insecticidal. EOs are generally recognized as safe (GRAS) by the United States Food and Drug Administration (FDA, 2019). Therefore, they have an edge over synthetic drugs with the added advantage of being safe and non-toxic. The role of EOs in treating infectious, acute, and chronic diseases has been well documented (Stea et al., 2014; Elshafie and Camele, 2017; Aljaafari et al., 2021).

The interactions between the components of the EOs could affect their activities. Therefore, to obtain formulations with constant efficacy against diseases, it is vital to identify the components responsible for the biological effect (Rúa et al., 2019).

Several studies demonstrated the in vitro and in vivo antiparasitic activities of various EOs of medicinal plants against E. granulosus s.l. (Siles-Lucas et al., 2018; Ali et al., 2020).

Carvacrol and its isomer thymol are the main phenolic components of the EOs of thyme and oregano (Santoro et al., 2007). Their antibacterial (Kachur and Suntres, 2020), antioxidant (Amiri, 2012), antimicrobial (Salehi et al., 2018), pesticide (Vale et al., 2021) and antiparasitic (Youssefi et al., 2019a, 2019b) activities have been demonstrated.

The efficacy of thymol and carvacrol was shown against protoscoleces (PSCs), microcysts and cyst of E. granulosus s.s., as well as their in vivo effect on infected mice (Elissondo et al., 2008, 2013; Fabbri et al., 2016; Maggiore et al., 2015). In addition, thymol and carvacrol were also effective against E. multilocularis metacestodes ex vivo and in vivo, and when combined with ABZ, their effects were significantly enhanced (Albani and Elissondo, 2014; Albani et al., 2015; Lopez et al., 2022). In the present study, we evaluated the in vitro, ex vivo and in vivo effect of the combination of carvacrol and thymol against E. granulosus s.s. larval stage.