Benign theileriosis is currently a disease of interest and research in NSW. The initial disease syndrome occurred in adult cows usually introduced from the west and south to coastal regions. In this syndrome adult cattle were typically anaemic, jaundiced and may abort. Recently a second syndrome has been seen in calves.
Disease occurred in a beef property located at Corndale, near Lismore. The property has cows and calves at pasture and also foster mothers to rear introduced calves. Five deaths occurred in a group of 8 homebred pasture based unweaned calves 6-14 weeks of age. An initial diagnosis of pneumonia was made by a private vet early in the outbreak and trimethoprim-sulfa and oxytetracycline antibiotics were prescribed to 2 of the calves before their death. No clinical improvement was seen with treatment.
On two calves findings were similar and included white lungs, except for red/purple colouration in the cranioventral lung fields. The cranioventral lung areas were also thickened. The liver appeared slightly swollen, yellow and with an enhanced periacinar pattern. In one of the calves there was increased pericardial fluid containing fibrin. The other calf had mild diarrhoea and a large quantity of mud in its abomasum. Pneumonia/sepsis and anaemia were suspected from the necropsies.
Histopathology results on the lung indicated a florid neutrophilic bronchopneumonia. Liver histopathology showed a severe cholestasis with a mild patchy periacinar hepatocellualr necrosis. There was a culture of Bacillus and Pseudomonas from lung and Aeromonas from intestine. Salmonella was excluded.
Lung histopathology showed severe suppurative bronchopneumonia with lymphoid hyperplasia. Liver histopathology showed hepatic necrosis and degeneration that was periacinar with extramedullary erthropoiesis. Pestivirus antigen was negative on a splenic sample and there was no significant growth on cultures from lung and liver swabs.
Healthy calf cohorts
All three calves had normal packed cell volumes (PCV) of 32, 33 and 43. Two calves had Theileria parasitaemias of 5 %. The other calf had a parasitaemia of 6%. Two calves had regenerative changes noted in their erythrocytes (anisocytosis, polychromasia) and also Howell Jolly bodies. Faecal egg counts were negative in these calves.
It is suspected that this group of young calves was exposed to Theileria parasites which caused red cell destruction. Although the PCVs were not low at testing the white appearance of lungs, liver changes suggesting anoxic damage and regenerative RBC response in healthy calves is suggestive of previous haemolysis. Haemonchus contortus was excluded by necropsy and a negative FEC. Theileria disease is suspected to be one factor in the calf mortalities from pneumonia.The anaemic calves would have impaired organ function and presumably some degree of immune suppression predisposing to bacterial pneumonia.
Other factors predisposing to the pneumonia include humid weather, wet muddy conditions, mud on udders, environmental mastitis in mothers, recent introduced stock and mixing of introduced and homebred stock. It is not surprising that a range of organisms was cultured reflecting the muddy environment and its mother's mastitic milk. Private veterinarians and LHPA veterinarians should be alert to the role Theileria parasitaemia may cause in predisposing young calves to other disease.