Observation of a novel Babesia spp. in Eastern Grey Kangaroos (Macropus giganteus) in Australia

Abstract

The roles and epidemiological features of tick-borne protozoans are not well elicited in wildlife. Babesia spp. are documented in many domestic animals, including cattle, horses, pigs, dogs and cats. Three cases affecting eastern grey kangaroos are described. The kangaroos exhibited neurological signs, depression and marked anaemia, and microscopic examination of blood smears revealed intraerythrocytic piroplasms. One to seven intraerythrocytic spherical, oval, pyriform and irregularly-shaped parasites consistent with Babesia spp. were seen in the blood smears and the percentage of infected erythrocytes was estimated to be approximately 7% in each case. Data suggest that the tick vector for this kangaroo Babesia sp. is a Haemaphysalis species. For Case 2, ultrastructural examination of the erythrocytes of the renal capillaries showed parasites resembling Babesia spp. and 18 of 33 erythrocytes were infected. DNA sequencing of the amplified 18S rDNA confirmed that the observed intraerythrocytic piroplasms belong to the genus Babesia. The phylogenetic position of this new kangaroo Babesia sp. (de novo Babesia macropus), as a sister species to the new Australian woylie Babesia sp., suggests a close affinity to the described Afro-Eurasian species Babesia orientalis and Babesia occultans suggesting perhaps a common ancestor for the Babesia in kangaroos.

Keywords: Apicomplexan; Babesia; Haematology; Kangaroo.

Graphical abstract

Fig. 1

Photomicrograph of a blood smear from an Eastern Grey kangaroo stained with Giemsa and showing the presence of Babesia species merozoites. Bar = 10 μm.

Fig. 2

Photomicrograph of blood smears stained with Diff-Quik (A) and Giemsa (B–F) from eastern grey kangaroos (Cases 2 and 3) showing diverse forms of Babesia including paired merozoites (2A), multiple ring-shaped trophozoites with a chromatin dot (2B), a large ring-shaped trophozoite with three chromatin dots (2C), ring-shaped trophozoite with a pair of buds in early dividing stage (2D), two dividing trophozoites with a cytoplasmic bridge (2E), and a clump of diverse forms of extraerythrocytic Babesia (3F). Bar = 10 μm.

Fig. 3

Electron micrographs of Babesia spp. (Case 2) within an erythrocyte. Nucleus (N); host cytoplasm (HC); endoplasmic reticulum (ER); ribosome (RI); mitochondria (MC), and invagination (I). Bar = 0.5 μm.

Fig. 4

Minimum evolution phylogenetic tree based on a 1560 bp 18S rRNA alignment for representatives of the genus Babesia including the new kangaroo-infecting species (in bold and underlined) originating from Cases 1 and 2. Also underlined and in bold are other species sequenced as part of this study. Branch support is shown with a ∗ where all tree building methods (parsimony, distance and likelihood) had at least 70% bootstrap and Bayesian support.