HEMATOLOGICAL CHARACTERIZATION OF HEAVY TICK INFESTATION IN KOALAS (PHASCOLARCTOS-CINEREUS)

The haematological effects of heavy tick infestation were investigated in eight koalas. In six koalas with uncomplicated tick infestation er ythroid regeneration was characterised by enhanced reticulocytosis, in creased numbers of circulating nucleated erythroid cells (CNEC) and th e occurrence of erythrocyte granular inclusions (EGI). EGI were determ ined from transmission electron microscopy to be primarily mitochondri a with ferruginous micelles between cristae. Recovery from anaemia too k 3-5 weeks. Leucocyte changes on recovery were restricted to increase d lymphocytes for five and increased eosinophils for four of the six k oalas. In the two koalas with underlying disease and tick infestation the anaemia was still characterised by increased levels of CNEC and th e presence of EGI but enhanced reticulocytosis was absent or limited. These results suggest that enhanced reticulocytosis is a good indicato r of regenerative anaemia in the koala. Enhanced CNEC and EGI may acco mpany the regenerative response but their presence alone may not be su fficient to indicate regeneration.