Effects of experimental Plasmodium collidatum infection in resident spotted doves (Spilopelia chinensis) in Thailand

Avian malaria is a mosquito-borne disease caused by Plasmodium apicomplexan protozoan parasites, such as the host-generalist P. collidatum . The disease is associated with high virulence, characterized by severe parasitemia and visceral organ damage leading to high mortality. In Thailand, P . collidatum infects both captive and wild birds across diverse geographic regions. However, the effects of P . collidatum infection in resident species remain understudied. In this study, the Spotted Dove ( Spilopelia chinensis ) was selected as a representative species due to its diverse habitats. The effects of P . collidatum pathogenicity on host response were investigated across the erythrocytic and exo-erythrocytic stages. Plasmodium collidatum was isolated from naturally infected Spotted Doves and cultivated for experimental infection. The development of infections was investigated over 48 days. The erythrocytic stage was monitored by microscopic examination of blood smears and by molecular analysis for detection of the cytb gene fragment. Post-experiment, the exo-erythrocytic stages of P . collidatum were investigated in visceral organs via hematoxylin–eosin staining. Hematology and clinical blood chemistry were compared between the infected and control groups. Morphological analysis and Bayesian phylogenetics confirmed the parasite used as P . collidatum . Although no mortality occurred during the experiment, infected Spotted Doves infected with P . collidatum exhibited significant pathological changes. Erythrocytic stages were characterized by a high proportion of trophozoites, with peak parasitemia occurring at 36 days post-inoculation. Hematological and clinical blood chemistry profiles indicated a cell-mediated host response and signs of anemia. Exo-erythrocytic stages were detected in the brain, heart, muscle, lungs, liver, spleen, and kidneys. These findings, corroborated by cytb detection, confirm that the infection caused systemic tissue damage. The high virulence and severe pathogenicity of P . collidatum infection were demonstrated in resident Spotted Doves. The infection followed a distinct trajectory, including early inflammation during the pre-patent period and extreme physiological stress. Examination of pathology revealed that the parasite caused severe mechanical obstruction of blood capillaries, resulting in extensive tissue damage across multiple organs.