CASE NOTES

BENIGN THEILERIOSIS ON THE MID NORTH COAST

Ian Poe, District Veterinarian, Mid Coast Livestock Health and Pest Authority, Kempsey

Posted Flock & Herd March 2011

Background

Over the last 4 years a considerable number of cases of clinical disease attributable to Theileria spp. have occurred in cattle on the Mid North Coast of NSW. The disease is characterised by a regenerative haemolytic anaemia. Common presentations of disease include late term abortions, stillbirths, dystocia, weakness, lethargy and death. Clinical findings include inappetance, pyrexia, tachycardia, tachypnoea, pale mucous membranes and jaundice.

Initially disease was primarily seen in cattle introduced from areas of western and southern NSW and Victoria. In 2010 a number of cases of Theileriosis in 2-3 month old home bred beef calves were seen. This report describes a number of Theileriosis-related issues faced by one beef producer near Wauchope, NSW.

HISTORY AND RESULTS

I was first contacted by the owner of this property in June 2010 after a 2 yo Angus bull he had recently purchased from Narrabri, NSW had died. The local private vet performed a necropsy and diagnosed Theileriosis. The 40 ha property is located 10 kms west of Wauchope on the Hastings River. The property runs a small Angus herd of about 80 breeders. In October 2010, I was contacted, when the owner wished to introduce another bull from Rylstone, NSW. It was decided that we would monitor this animal from the day of introduction to determine how quickly organisms were detectable in red cells on a blood smear, and also to attempt treatment prior to the onset of clinical signs. The bull was introduced on the night of 12 October 2010. The Angus bull weighed approximately 1000 kg and was in excellent body condition on arrival. Numerous bush ticks (Haemaphysalis spp.) were noted on the bull the day after introduction, and the bull was treated fortnightly with Bayticol Cattle Dip and Spray (Bayer Australia Ltd.) at a rate of 10ml/10L of water, in an attempt to minimise the tick burden. Blood collected in EDTA was collected at several visits following introduction, rectal temperature was taken at each visit. Samples were sent to EMAI Veterinary Laboratory, for packed cell volume (PCV) and blood smear examination for the presence of Theileria organisms. The results are summarised in Table 1.

On the second visit on 22/10 the bull had an elevated rectal temperature of 40.4°C. Given the history of the previous bull a decision was made to treat with imidocarb dipropionate 120mg/ml s c (Imidox, Parnell). No organism were detected until 2/12/2010 after the bull had been on the property for 41 days. The bull was again treated with imidocarb on 9/12/2010. Blood collected on that day revealed a parasitaemia of 10%. On 21/12/2010 the parasitaemia had dropped to 2.5%. This bull is still alive and well after 4 months on the property.

Table 1. Results of examination and testing of the introduced Angus bull.

DATE	DAYS POST-ARRIVAL	PCV	Est. % RBC parasitised	TEMP (°C)	TREATMENT
13/10/2010	1	0.39	Neg	38.5
22/10/2010	9	0.48	Neg	40.4	Imidocarb, 2.5mls/100kg
26/10/2010	13	0.40	Neg	39.3
1/11/2010	19	0.42	Neg	39.0
2/12/2010	41	0.30	13	39.1
9/12/2010	48	0.27	10	39.3	Imidocarb, 2.5mls/100kg
21/12/2010	60	0.31	2.5	38.5

On the 3^rd visit on 26/10/2010 the owner asked if I would look at a sick calf he had, which could not walk to the yards with the rest of the mob. It was still in the paddock. This calf was approximately 3 months-old and had been well up until that day. The calf was moribund but was in excellent body condition, had a low burden of bush ticks (Haemaphysalis spp.), and the mucous membranes were extremely pale. The calf died during examination and blood was collected into EDTA immediately. A necropsy revealed a liver enlarged approximately 1.5 times normal size, with rounded margins. There was diffuse orange discolouration of the liver extending through the parenchyma. The spleen was enlarged 1.5-2 times normal size. Images of several affected organs are shown in Figure 1. The carcass was generally pale, however, jaundice was not a feature. The heart, lungs and gastrointestinal tract appeared normal. A variety of tissues were submitted for histopathological examination to EMAI.

The laboratory revealed a PCV of 14% and the blood smear showed moderate anisocytosis with mild polychromasia and basophilic stippling. Howel-Jolly bodies and moderate numbers of nucleated red blood cells were noted. Theileria spp. organisms are noted at a frequency of 5%. The liver showed multifocal degeneration of periacinar hepatocytes consisting of lipid vacuolation, feathery vacuolation or hypereosinophilia. Subcapsular, sinusoidal and periportal extramedullary haematopoiesis was identified. Intracellular and intracanalicular golden-brown pigment (bile) was present in moderate quantities suggesting cholestasis. The spleen showed moderate expansion of periarteriolar lymphoid sheaths. Numerous nucleated red blood cells were noted in the red pulp in addition to scattered nuclear debris and moderate numbers of bacilli. The kidney showed moderate degeneration of proximal tubular epithelial cells with loss of brush border, vacuolation of the cytoplasm and desquamation of cells into the lumen. Granular golden-brown pigment was noted in many tubular epithelial cells.

The histopathologist commented that the changes seen were consistent with the anaemia. Hepatic changes suggested a subacute time scale and changes in the reactive spleen were suggestive of haematopoetic activity and the breakdown of red cells.

Figure 1. Images of organs taken at necropsy. From left – liver, liver cut surface, spleen.

Discussion

Following the diagnosis of Theileriosis in calves on this property, a group of 10 calves were recruited for inclusion in a research project coordinated by Graham Bailey, NSW Industry and Investment, and funded by Meat and Livestock Australia. Hopefully results from this and other projects in the area will provide more information on Theileria spp. infection in home-bred calves.

Treatment options available for Theileriosis are currently limited in Australia. Antimicrobials being used include oxytetracycline, halofuginone and imidocarb dipropionate. Results have been variable with all 3 drugs. Halofuginone (Halocur Oral Solution 0.5 mg/mL, Intervet/Schering-Plough Animal Health) at a dose rate 10 times (1.0 mg/kg) the recommended rate for cryptosporidiosis, has been used by some. However, side effects, including oesophageal and oral irritation have been noted (P Carter and, A Poynting, pers comm.). This irritation may be reduced if treatment is followed by irrigation of the oral cavity with liberal amounts of fresh water. In an attempt to minimise losses in home-bred beef calves I have been recommending injections of imidocarb dipronionate at a dose rate of 2.5mls/100kg s c in 1 to 3 month-old calves as a prophylactic treatment for animals on properties where the mortality rate in calves due to Theileriosis has been around 5%.

References

P Carter BVSc. Tick Fever Centre Queensland Department of Employment, Economic Development and Innovation. Personal Communication 2009.
Arthur Poynting BVSc. Gloucester Veterinary Hospital. Personal communication 2010.