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Background and Aim: Trypanosoma evansi is a blood and tissue protozoan parasite affecting domestic and wild animals. The T. evansi Thai strain, namely, T. evansi from dairy cattle number 953 (TEDC 953) strain, has been successfully isolated from dairy cattle and cultivated in vitro . The in vitro -cultivated parasite is useful for biological studies, evaluation of novel chemotherapeutic agents, and production of antigens for diagnostic tests. This study aimed to observe the histopathology and virulence of an in vitro -adapted T. evansi TEDC 953 strain in vivo ., Materials and Methods: The histopathology and virulence of the TEDC 953 strain were clarified in mice. Six mice were infected with 1 × 10 5 trypomastigotes of TEDC 953 strain intraperitoneally, and four mice were in the negative control. Parasitemia was monitored daily, and the mice were euthanized on 30 days post-infection (DPI). Internal organs were collected for histopathological examination using hematoxylin and eosin staining., Results: Histopathological lesions were found in the liver, lung, heart, kidney, spleen, and brain of the inoculated mice. The main histopathological feature was lymphoplasmacytic inflammation in parenchyma and perivascular areas of multiple organs, and the severity of histopathological changes was related to the presence of trypomastigotes in the regional vessels. Granulomatous inflammation was seen in meninges, pleura, renal capsule, renal pelvis, and spleen of some infected mice. Four mice died at 17, 24, 26, and 27 DPI with an average parasitemia of 4.05 × 10 11 trypomastigotes/mL. The average survival time was 23.5 DPI (mice = 4)., Conclusion: This study confirmed that the TEDC 953 strain is infectious and pathogenic in mice after the continuously cultivated in vitro . To replace the use of experimental animals, the in vitro -cultivated parasite can be used instead in further studies., Competing Interests: The authors declare that they have no competing interests., (Copyright: © Phongphaew, et al.)