Addendum A

Haematozoan Infection in Young Eastern Grey Kangaroos

RW Cook, GC Fraser, and WJ Hartley

Presented at Australian Veterinary Association Pathology Meeting, Brisbane 1996

Since 1994, a syndrome of severe anemia associated with haematozoan infection, has been recognized in eastern grey kangaroos (Macropus giganteus) on the north coast of NSW.  All affected animals had been reared for varied periods by wildlife carers, and developed clinical signs at 6 to 13 months of age, while in care or soon after release.  In addition to marked anemia (heamatocrits were 0.06 to 0.12g/L), the initial cases had heavy burdens of ticks (ixodes and heamaphysalis spp.) and a tendency to bleed from tick attachment sites when ticks were removed.  Polydipsia and polyuria were reported in some affected animals.

The peripheral blood of anemic animals that subsequently died, had minimal evidence of erythrocyte regeneration, and usually less than 2% of erythrocytes contained round or elongated protozoan organisms 1-4 mm in diameter in singles, pairs or other binary multiples.  Examination of histological sections (and impression smears) of a range of organs included kidney, liver, spleen, heart and brain.     Revealed sequestration of parasitised erythrocytes, and variable formation of schizont-like forms within blood vessels.  These changes were most marked in the renal glomeruli, where schizont-like forms distended the capillaries of glomerular tufts.

Two affected animals had a markedly regenerative anemia (haematocrits of 0.11 and 0.12g/L), and improved clinically, after intravenous treatment with imidocarb. 

The identity of the presumed Apicomplexan parasite, and its arthropod vector, and the epidemiology of infection remain to be determined.  However, the susceptibility of these young eastern grey kangaroos to clinical disease may be a result of a reduced natural exposure to ticks throughout their period “in care”.

Acknowledgement

We thank the wildlife carers, particularly Judy Petersen and Dianne Ward, and veterinarians, Drs Mark Crane, Kim Elvery and Terry Johnson for providing histories and submitting specimens from these cases.

RW Cook and GC Fraser – NSW Agriculture, Regional Veterinary Laboratory, Wollongbar, NSW, 2477

WJ Hartley – Taronga Zoo