The agent associated with a syndrome of anaemia and debility in eastern grey kangaroos (Macropus giganteus giganteus) on the north coast of New South Wales (NSW) and in South-Eastern Queensland (QLD) is herein characterised as a novel Babesia spp. A detailed investigation of numerous cases from two outbreaks of this disease during 2012 in NSW and QLD together with a review archival material from cases recognised since 1994 at the former Regional Veterinary Laboratory Wollongbar in NSW. Affected animals have marked anaemia, lethargy, weight loss, variable neurological signs (altered mentation, vision deficits and loss of pupillary light reflexes) and an increased blood clotting time. At necropsy, the blood is watery and there is generalised tissue pallor and oedema and splenomegaly.
In anaemic animals, typical intraerythrocytic Babesia organisms are detected in less than 2% of erythrocytes in peripheral blood smears. However, examination of histological sections (and impression smears) of a range of organs including kidney, brain, spleen, and heart reveals parasitised erythrocytes and extraerythrocytic aggregates of zoites within vessels. These changes are most prominent within capillaries of the renal glomerular tufts and brain. Phylogenetic analysis of 18s RNA and HSP70 genes extracted, amplified and sequenced from samples of kidney, brain and blood from affected animals clearly indicates that the organism resides within the genus Babesia and is a species endemic to Australia.
Based on historical records and recent reports, the spectrum of clinical findings and geographic range of infection appear to be expanding. Subsequent outbreaks have outlined the need to characterise the transmission and pathogenesis of disease associated with this novel species of Babesia.