Andrographolide as a selective anti-Theileria annulata drug molecule with low host cell cytotoxicity.

Bovine tropical theileriosis, caused by Theileria annulata, is a significant economic burden in endemic regions. The limitations of current control measures necessitate the development of new therapeutic agents. This study evaluated the anti-Theileria potential and host cell safety of rutin, andrographolide, dodecyltrimethylammonium bromide (DTAB), and fusidic acid. Antiparasitic efficacy was assessed using a resazurin-based growth inhibition assay on T. annulata-infected bovine lymphocytes. Cytotoxicity and haemolytic activity were evaluated using healthy bovine peripheral blood mononuclear cells (PBMCs) and red blood cells (RBCs), respectively. All compounds exhibited concentration-dependent anti-theilerial activities. Andrographolide was the most potent (IC₅₀ = 542.89 µM), followed by fusidic acid (IC₅₀ = 573.64 µM) and DTAB (IC₅₀ = 633.98 µM), while rutin showed weak activity (IC₅₀ = 2748.04 µM). In the cytotoxicity assay, andrographolide was the least toxic to PBMCs (15.06% cell death), whereas DTAB and rutin showed significantly higher toxicity. All compounds were non-haemolytic (<5% haemolysis). This study identified andrographolide as the most promising candidate, demonstrating potent anti-Theileria annulata activity coupled with minimal host cell cytotoxicity and haemolysis, indicating a high selective index. Andrographolide warrants further investigation as a lead compound for developing safer therapies against bovine tropical theileriosis.