Final Diagnosis - Bovine Leukosis in a neonatal calf
History: A reportedly 1-day-old crossbred female calf was submitted dead for necropsy with a history of hemorrhage from multiple organs and death. Per history, the calf was found cold and weak with blood oozing from the anus and vulva. Petechial hemorrhages were observed in the oral cavity, gingiva and sclera.
Gross findings: Petechial hemorrhages were observed throughout the serosal surface of the small intestine. The rectum was edematous and hemorrhagic on the serosal surface; however, on cut section, the mucosal surface did not show evidence of hemorrhage. Ecchymotic hemorrhages were present in the mesentery and paintbrush hemorrhages were visible on the serosal surface of the abomasum. The abomasum and forestomachs were almost empty but contained a small quantity of translucent mucoid material (amniotic fluid). Terminal parts of the colon and rectum contained formed feces (meconium), which had a pasty consistency. The urachus was hemorrhagic and edematous. The liver was pale tan and slightly firm in consistency, granular in appearance and had a thickened capsule. Multifocal to diffuse hemorrhages were also observed in the skeletal muscles, epicardium and endocardium. Lymph nodes were dramatically enlarged throughout the body. The mesenteric and tracheobronchial lymph nodes were markedly enlarged (up to 6x3x2 cm).
Histologic findings: Liver: Multifocal to coalescing nodules and random aggregates of discrete round cells with distinct borders were effacing and often compressing the hepatic parenchyma. Most of these nodular aggregates were centered in the portal areas and had a pattern of spreading out circumferentially into the adjacent hepatic parenchyma from the portal tracts. Random aggregates of such cells were also present multifocally in the hepatic sinusoids and were distributed diffusely beneath the hepatic capsule. These cells had irregularly round to oval large nuclei with marginated, clumped to stippled chromatin rimmed by pale, scant cytoplasm. There was moderate anisocytosis and anisokaryosis. The hepatic arteries were multifocally ectatic and often contained the cells described above. Mitoses were 1-2 per HPF.
Kidneys: Multifocally, the interstitium was expanded by cellular aggregates of similar nature as seen in the liver and was especially prominent around blood vessels.
Lymph nodes and bone marrow: Neoplastic round cells, similar to those present in the liver and kidneys, diffusely effaced the normal cortical and medullary architecture of the lymph nodes. The bone marrow was hypercellular, with most of the cell population comprised of neoplastic round cells.
Heart: Major changes included multifocal areas of hemorrhage, swelling and cytoplasmic vacuolation of cardiomyocytes, and multifocal mild to moderate lymphocytic and histiocytic inflammation and diffuse areas of hemorrhage in the epicardium. Lymphocytes may be neoplastic.
Skeletal muscle: Hypereosinophilia of several muscle fibers, hemorrhage, edema, cellular infiltration consisting of macrophages and lymphocytes (possibly neoplastic) often centered on blood vessels, were the main alterations.
Lungs: Hemorrhage, lympho-histiocytic inflammation in the interlobular septae and multifocal hemorrhages in alveolar spaces were present. Multifocally, alveoli were collapsed with slit-like alveolar spaces. Mild expansion of interstitium with mononuclear cell infiltration (possibly neoplastic lymphocytes) and fibrin and perivascular hemorrhages were prominent changes.
Discussion: A diagnosis of Bovine Leukosis (congenital) was made in this case as per histological observations. Perinatal infection with BLV is the most likely cause of lymphosarcoma in this calf. Malignant lymphoma was found to have the greatest incidence among neoplastic diseases in calves according to various studies. The congenital form of this disease is most commonly multi-centric. Diagnosis of disease prevalence in the herd can be made by ELISA or AGID tests on serum samples although calves to 6-7 months of age having received colostrum with antibodies might return false positive results. Also, animals in the early stages of infection, animals with poor immune response, and cows immediately prior to and after calving, do not make good candidates for such serological testing. Peroxidase linked assay (PLA) and nested-PC have recently been reported to have high efficiency in making an accurate diagnosis of Bovine Leukosis.
-by Dr. Gopakumar Gopalakrishnan, ADDL graduate student