Novel Haemocystidium sp. Intraerythrocytic Parasite in the Flatback (Natator depressus) and Green (Chelonia mydas) Turtle in Western Australia.

Malaria and other haemosporidian parasites are common in reptiles. During baseline health surveys of sea turtles in Western Australia (WA), haemosporidian parasites were detected in flatback (Natator depressus) and green (Chelonia mydas) turtle erythrocytes during routine blood film examination. 130 blood samples were screened via polymerase chain reaction (PCR), including 105 N. depressus, 20 C. mydas, and 5 olive ridley turtles (Lepidochelys olivacea). A novel Haemocystidium sp. was identified, detected exclusively in foraging turtles and not in nesting turtles. The combined prevalence by microscopic and molecular methods was 16.9% (22/130), primarily affecting immature C. mydas (77.3%; 17/22). Mature N. depressus were also affected (22.7%; 5/22). DNA sequencing of a partial fragment of the mitochondrial cytochrome b (cytb) gene together with phylogenetic analysis identified two different Haemocystidium sp. genotypes, A and B, with genotype A being most prevalent. The phylogenetic analysis showed close genetic relationships to Haemocystidium sp. in freshwater and terrestrial turtles, suggesting a shared evolutionary lineage despite ecological differences. Preliminary analysis indicates that this parasite is incidental, as no association between health and parasite presence or grade was detected. This study provides the first formal detection of haemosporidian parasites in sea turtles, contributing essential baseline data while highlighting their evolutionary significance and host-parasite ecological relationships.