Sporadic leukosis in cattle

Sporadic bovine leukosis (SBL) is a rare neoplastic disease in cattle. It represents a unique challenge for veterinary medicine due to its sporadic occurrence, peculiar clinical presentation and unclear etiology. SBL manifests in four forms: juvenile lymphosarcoma, adult multicentric leukosis, thymic lymphosarcoma and cutaneous lymphosarcoma. In contrast to enzootic bovine leukosis, which is caused by the bovine leukemia virus (BLV), there is no viral link in sporadic cases. They are thought to be caused by multifactorial interactions between genetic predisposition and environmental factors (e.g. carcinogens or other triggers). The diseases are not contagious. The aim of this paper is to review the current knowledge of SBL, focusing on the clinical presentation, diagnostic challenges and potential risk factors. Although sporadic leukosis accounts for a smaller proportion of leukosis cases in cattle compared to BLV-induced leukosis, the impact on affected individuals is severe. SBL must be differentiated from BLV-induced leukosis (absence of BLV antibodies in the blood and absence of BLV in the tissue), which is a reportable disease in the European Union. SBL usually affects younger cattle, but adult animals can also be affected. Adult multicentric leukosis clinically resembles enzootic bovine leukosis with multicentric lymphoproliferative foci and lymphadenopathy, but the affected animals are negative for BLV antibodies. The diseases are progressive and lead to the death of the animals. Diagnostic confirmation of SBL often requires a combination of histopathologic examination, immunohistochemistry and molecular analyses to differentiate it from other neoplastic diseases in cattle. Risk factors such as exposure to certain environmental toxins or genetic susceptibility are thought to play a role in the development of sporadic leukosis. Further research efforts are needed to elucidate the mechanisms underlying the development of SBL and to develop effective prevention and control strategies to control this sporadic but usually lethal disease in cattle population.