Haemoparasites are relatively common in many species of native Australian mammal; however, their potential role as disease agents and their influence on wildlife ecology is not well understood. The protozoan piroplasm Theileria ornithorhynchi is thought to cause little harm under normal circumstances, but in an immunosuppressed platypus may become a significant pathogen. A subclinical infection may become clinical when there is an alteration in the host-agent-environment relationship.
A tick-infested, juvenile female platypus was seen on the bank of the Murrumbidgee River near Oura during daytime following a flood and was brought into care. Blood was collected aseptically from the dorsal bill sinus and Diff Quik stained blood smears were prepared. Haematology revealed yellow plasma, a PCV of 0.17 and red cell count of 4.4 x 1012/l (reference ranges 0.49 - 0.51 l/l and 9.9 - 10.3 x1012/l respectively) and a marked regenerative anaemia with reticulocytes, anisocytosis and nucleated erythrocytes. Large numbers of erythrocytes contained parasites morphologically consistent with Theileria. The life cycle of this organism is unknown, but is believed to have developmental stages within the tick. A semi-nested PCR using extracted DNA from whole blood produced an 18S rDNA gene that aligned with other Theileria and Babesia genotypes. Haematology also showed a left shift and toxic changes in the neutrophils, a monocytosis and some phagocytosis of parasitised erythrocytes. Despite tick removal and PCV improvement; the platypus’ condition deteriorated, it died and was necropsied on day 5. Histopathology revealed a moderate erythroid hyperplasia of the bone marrow and spleen. Foci of hepatocellular necrosis and renal tubule deposits of bilirubin or haemosiderin were present. A pure growth of Klebsiella pneumonia was isolated from liver.
The animal’s death was attributed to a severe immune mediated haemolytic anaemia secondary to Theileria ornithorhynchi infection, accompanied by a terminal Klebsiella pneumoniae bacteraemia and septic hepatitis.