Theileriosis in six dogs in South Africa and its potential clinical significance.

Theileriosis is a tick-borne disease caused by a piroplasma of the genus Theileria that can causeanaemia and thrombocytopenia. Its clinical importance for dogs' remains poorly understood,as only some develop clinical signs. In this study, physical and laboratory findings, treatment and outcomes of six client-owned diseased dogs presented at the Onderstepoort Veterinary Academic Hospital are described retrospectively. In the dogs, Theileria species (n = 4) and Theileria equi (n = 2) were detected by a polymerase chain reaction (PCR)-reverse blothybridisation assay in blood samples, whilst PCR for Babesia, Anaplasma and Ehrlichia were negative. The most common physical findings were pale mucous membranes (five out of six dogs), bleeding tendencies (five out of six dogs) and lethargy (three out of six dogs). All dogs were thrombocytopenic [median 59.5 x 10(9)/L (range 13-199)] and five out of six dogs were anaemic [median haematocrit 18% (range 5-32)]. Bone marrow core biopsies performed in two dogs showed myelofibrosis. Theileriosis was treated with imidocarb dipropionate and the suspected secondary immune-mediated haematological disorders with prednisolone and azathioprine. Five dogs achieved clinical cure and post-treatment PCR performed in three out of five dogs confirmed absence of circulating parasitaemia. An immune-mediated response to Theileria species is thought to result in anaemia and/or thrombocytopenia in diseased dogs with theileriosis. A bleeding tendency, most likely secondary to thrombocytopenia and/or thrombocytopathy, was the most significant clinical finding in these cases. The link between thrombocytopenia, anaemia and myelofibrosis in theileriosis requires further investigation and theileriosis should be considered a differential diagnosis for dogs presenting with anaemia and/or thrombocytopenia in endemic tick-borne disease areas.