A 3-4 month old calf from a mob of 40 cows and calves developed a fever and enlarged submandibular lymph nodes on a property in the Nandewar Ranges east of Narrabri. They were grazing lush native pasture, and there had been no introductions to the group.
The owner sought telephone advice from his private practitioner who suspected calf diphtheria. The calf was treated with Tolfedine (tolfenamic acid), Neomycin (neomycin sulphate) and later penicillin without improvement. The calf continued to deteriorate and died approximately three weeks after the onset of clinical signs.
The calf carcase appeared in thin body condition. There was a generalised lymphadenopathy with affected lymph nodes in all body systems examined. They ranged in size from 3cm to 15cm diameter. On cut surface, most nodes appeared extremely reactive with many having purplish necrotic areas (Figure 1). Many contained petechial haemorrhages. One submandibular lymph node contained purulent material. There were no lesions on the larynx. The tip of the epiglottis was inflamed but not ulcerated. The thymus appeared enlarged and was covered in petechial haemorrhages (Figure 2). There were also petechial haemorrhages on the epicardium. The liver was enlarged by approximately 30% and had a grainy appearance with cream coloured flecks throughout (Figure 3). The liver sinusoids appeared enlarged. The spleen was enlarged and the parenchyma pulpy (Figure 4). The caudal abdomen contained a mass of purple/black lymph nodes which appeared to occlude the large intestine (Figure 5).
Histopathology of lymphoid tissue and the liver revealed: Lymphosarcoma, juvenile, multicentric - Sporadic Bovine Leukosis.
Sporadic Bovine Leukosis (SBL) is rarely diagnosed, with around 1 individual per 100,000 cattle estimated to be affected (Oliver-Espinosa et al., 1994).
SBL has 3 recognised forms:
The clinical course and post mortem findings in this case study closely resembled the descriptions available for Juvenile SBL in the literature, including a 2 month old Angus heifer with sporadic juvenile lymphoma presented to Washington State University (Harbo et al., 2004).
In contrast to Enzootic Bovine Leukosis (EBL), which is caused by bovine leukaemia virus (BLV) and has an incubation period of around 4 to 5 years; SBL occurs in animals less than 3 years of age and is traditionally thought not to be associated with BLV (Radostits et al., 2007). However a Canadian study found that 4 of 10 cattle affected by lymphoma and less than 3 years of age in a known BLV-infected herd were positive for BLV provirus in tumour DNA, detectable by PCR Jacobs et al., 1992). This result suggests that some SBL cases may be associated with BLV.
The presence of EBL, in dairy herds especially, causes economic loss through decreased production and increased mortality of cattle with tumours and restricted trade of cattle, semen, ova, and milk products from affected herds and regions. The virus has been eliminated from dairy herds in NSW but beef cattle remain infected at a low prevalence (NSW DPI, 2011). In cases where SBL is confirmed in a beef herd and the calf's dam tests positive to BLV antibodies, investigation to confirm whether the cow originated from a dairy property is warranted.