One of 15 2-2.5-year-old steers presented as alert but lethargic with weight loss over several months, partial blindness and three swollen legs. The differentials, lead poisoning, sporadic bovine encephalomyelitis, pestivirus and hepatic encephalopathy were ruled out (as was transmissible spongiform encephalopathy). The diagnosis, suspected at necropsy and confirmed by histology, was reasonably obvious with the benefit of hindsight.
One of 15 2019 drop steers, having lost weight for 6-8 weeks, presented as thin, lethargic and apparently blind with a swollen front leg. The steers had been weaned over 12 months previously and were recently drenched. The mob has been grazing a paddock dominated by blue heliotrope (Heliotropium amplexicaule) until a few weeks prior. There were no known sources of lead. Of interest, the owner commented that he had previously seen steers, presumably intoxicated by blue heliotrope, lose weight and become dull and aggressive before dying.
The steer, treated symptomatically by one of us (GC), responded initially but then continued to deteriorate and subsequently died.
The 2.5-year-old Angus steer was examined on the 26 July 2021. It had grown slowly compared to its cohorts and was in fat score 2.0. When examined in the yard the steer appeared to be partially blind but was able to avoid objects. On examination the steer had weak tongue withdrawal but no oral lesions. There was no menace response in either eye, but the right pupil constricted with light while the left pupil only partially constricted with light. There was slight bilateral exophthalmos. The right front leg was swollen, particularly around the carpus, and both hocks were distended. The heart rate was slow at about 50 bpm and there was reduced rumen motility. The steer had a normal temperature and the prescapular and prefemoral lymph nodes were not enlarged.
INITIAL LABORATORY FINDINGS 26 July 2021
|Biochemistry — Sample 11322|
The steer died and was necropsied on 2 August 2021. Multiple petechial haemorrhages were seen on most serosal surfaces and fascial planes, with more extensive haemorrhages over the serosa of the omasum, abomasum and duodenum. The right apical lung lobe was consolidated and the liver was enlarged, brownish orange with rounded edges. There were extensive coalescing haemorrhages over both internal and external surfaces of the heart. The pharyngeal lymph nodes were enlarged and fleshy and there were areas of necrotic bone and cartilage in the frontal sinuses and behind the ethmoid plate.
Enzootic bovine leucosis ELISA was negative and Chlamydia complement fixation test was negative (<8). EDTA blood was PCR negative for Malignant Catarrhal Fever (tested because of vasculitis on histopathology) and tail hair samples were negative for pestivirus antigen (PACE). Samples tested negative for prion protein.
Histopathology revealed lymphoma affecting the liver, kidney, pharyngeal tissue/tonsil, lymph node, bone marrow, brain and heart. Within the tonsil and lymph node, sheets of neoplastic cells infiltrated and effaced normal architecture, while infiltrates were multifocal in the kidney and periportal within the liver. Within the heart and brain, small numbers of neoplastic cells were within and around blood vessels. Neoplastic cells were large, round, had distinct cell borders, scant cytoplasm and contained a large nucleus with stippled chromatin and a single nucleolus. Mitotic figures averaged approximately 1-3 per high power field. Neoplastic cells were present within vessels in multiple tissues. Within the section of lung examined, there was a marked, acute, widespread fibrinonecrotising pleuropneumonia with vasculitis, thrombi, oedema and abundant intralesional bacteria. Within and surrounding a suspected section of lymph node, in addition to sheets of neoplastic round cell infiltrates, there were marked, multifocal to extensive areas of fibrin and necrosis, multifocal haemorrhage and fibrinonecrotising vasculitis. Within the cerebellum, there was a focal, mild area of malacia and haemorrhage.
In hindsight this was clearly a multifocal disease affecting the brain, optic nerves, liver, lymphatic system, lungs, heart and peripheral circulation. A widely disseminated lymphoma is the most likely cause.
As this case was serologically negative for enzootic bovine leucosis virus (EBL), it is classified as sporadic (or atypical) bovine leucosis (SBL). SBL typically has three forms; juvenile (usually in calves less than six months and characterised by generalised lymphadenopathy), thymic (most commonly in animals from 6 months to 2 years) and the cutaneous form (in cattle 1-3 years of age). However atypical cases affecting older cattle and different organs have been reported and cases can have characteristics of more than one category (Constable et al. 2017, Grünberg and Eisenberg 2013, Hendrick 2002).