Bovine Leukosis: Classification, Clinical Findings, Clinical Pathology, Diagnosis, Necropsy and Control Measures

Abstract

Bovine leukosis is divided into two types: enzootic bovine leukosis (EBL), which is caused by bovine leukemia virus (BLV) infection, and sporadic bovine leukosis (SBL) of unknown cause. EBL is a non-benign tumorous disease of the lympho-reticular system in cattle. It is manifested by inveterate low-level viremia and a considerably long passivity period. BLV is an oncogenic class of the Delta retroviruses, and it is exceedingly linked to the human T-cell leukemia virus. Worldwide, BLV hits cattle causing huge financial losses. Genetic tendency plays a vital role and is shown in the fact that few cattle are apparently affected. Infected animals are constant carriers of the virus; however, infected cows are asymptomatic, with few cattle showing passing viremia. Three to four months post-infection, BLV virus is difficult to be sequestered from these cows. Almost thirty percent of infected cows are sero-convert and may develop constant lymphocytosis within three months to some years post-infection. Only one to five percent of carrier cattle show the tumorous disease. SBL is typically classified into three forms according to onset age and lesion site: calf or juvenile form, thymic or adolescent form, and skin or cutaneous form. These forms are sporadic with no implicit infectious cause, like a virus, has been isolated for these forms. However, the popular form, enzootic or adult multi-centric form, is always linked with BLV infection. In the later form, affected cattle are usually four to eight years old, and neoplasms are usually located in the abomasum, uterus, cardiac right atrium, or superficial lymph nodes. Clinical manifestations, laboratory findings, diagnostic criteria, necropsy findings, and control measures are clarified. As a consequence of EBL, large financial losses occur due to the collapse of affected cattle, condemnation of diseased cases, loss of export benefits, and veterinary charges. This review was written to emphasize the categories, clinical findings, clinical pathology, diagnosis, necropsy, and control measures of bovine leukosis in cattle.