Yellow mealworm beetle (Tenebrio molitor) larvae as an alternative model for antileishmanial drug evaluation

Leishmaniasis is zoonotic disease caused by parasites of the genus Leishmania. Available treatments are limited and are associated with a range of adverse effects. The search for potential new drugs involves both in vitro and in vivo assays. Rodents are primarily employed as experimental models for in vivo assays. However, this practice raises ethical concerns, including issues related to environmental impact and animal welfare. Therefore, various alternative methods have emerged to avoid or reduce the use of mammals in laboratories for preclinical trials. The aim of this study was to evaluate Leishmania amazonensis infection in yellow mealworm (Tenebrio molitor) larvae. T. molitor larvae were infected with promastigotes (1 ×10⁵; 1 ×10⁶; and 1 ×10⁷) and assessed through survival curves, degree of melanization, parasitic load, cell proliferation, and oxidative stress levels measured by reduced Glutathione (GSH) and nitrite levels. Leishmania promastigotes which invaded T. motilor plasmatocytes transformed into intracellular amastigotes. Ten percent of larval death was observed after 24 hours in larvae that received 1 × 10⁵ and 1 × 10⁶ promastigotes and 20 % mortality was found for those that received 1 × 10⁷. The parasitic load revealed approximately 1750 parasites/larva infected with the highest concentration. Furthermore, the larvae showed a cellular response pattern similar to that seen in vertebrate host infections, with increased cell proliferation, activation of plasmatocytes, and elevated GSH and nitrite levels. This is the first study to establish T. molitor larvae as an alternative model for investigating Leishmania pathogenesis in invertebrates, proposing its use in preclinical trials for exploring potential new drugs to combat leishmaniasis.