Essential oils active against Anisakis nematode larvae

Anisakiasis is a human parasitic infection of the gastrointestinal tract that can cause severe abdominal pain, malnutrition, and vomiting. This parasitosis is mainly caused by larvae of the nematode Anisakis simplex, that reach the intestine through the consumption of raw and undercooked seafood, namely fish and cephalopods. Generally, it is undetected, but can sometimes be responsible for severe allergic reactions, namely anaphylaxis, caused by the production of immunoglobulin E in response to chemicals released by the dead larvae in the intestine. To date, no effective drug has been found against this digestive parasitosis and common anthelmintic treatments seem not be active against A. simplex. Essential oils (EOs) present a still fairly unexplored source for natural products with activity towards this parasite. The present work reviews the available literature on EOs tested in vitro against Anisakis nematodes, and compiles the EO composition and activity of the most active.

Over one dozen plant species were used as sources for the active EOs, mainly from Asteraceae, Lamiaceae, Apiaceae and Myrtaceae families. The lowest half maximal lethal concentrations (LC₅₀) were reported for Origanum syriacum and O. compactum EOs, both rich in the monoterpenoid carvacrol (83% and 50%, respectively. The EOs extracted from Tagetes minuta and Nepeta cataria were reported to be the fastest acting, with half maximal lethal times (LT₅₀) under 4 h, and were rich in the oxygenated monoterpene geraniol (55%) and the monoterpenic hydrocarbons β-ocimene (36%) and limonene (27%), respectively. Given their complex chemical composition, additive, synergistic and antagonistic interactions between EO compounds can be responsible for EO activity against this parasite.

A deeper analysis of the chemical structures active against Anisakis, and the nature of their interactions can be possible with further studies on this parasitosis.