Gary L. Cockerell

Seroprevalence of bovine immunodeficiency-like virus and bovine leukemia virus in a dairy cattle herd

To determine the prevalence of single vs. dual infection with bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV), sera (n = 95) from a dairy cattle herd were analyzed for anti-BIV and anti-BLV antibodies by an enzyme linked immunosorbent assay. Twenty-one percent (20/95) of samples were BIV-seropositive, while 52% (49/95) of the same samples were BLV-seropositive. A significantly greater percentage of BIV-seronegative samples were BLV-seropositive, 57% (43/75), than were BIV-seropositive samples, 30% (6/20). There was no significant correlation between data ranked from least to greatest amount of anti-viral antibody. Five cattle had persistent lymphocytosis (PL); all five were BLV-seropositive and two were BIV-positive. The mean anti-BLV titer was significantly greater in PL cattle, as compared at non-PL cattle, whereas there was no significant difference between the mean anti-BIV titer in PL cattle, as compared with non-PL cattle. These results provide additional information on the seroprevalence of naturally occurring BIV infection, and indicate that BIV can exist independent of other common infectious agents, such as BLV. Further, the results suggest that infection with BIV is not associated with an increased rate of infection with other infectious agents such as BLV.

The correlation between the direct and indirect detection of bovine leukemia virus infection in cattle.

Ninety-three cattle from a herd naturally infected with bovine leukemia virus (BLV) were tested for the presence of BLV infection by two indirect indicators, anti-BLV antibodies and lymphocytosis, and two direct indicators, BLV provirus and BLV gp51 antigen expression in peripheral blood mononuclear cells (PBMC). Forty-eight percent (45/93) of the cattle were seropositive, and of these, 53% (24/45) were provirus-positive. Freshly isolated PBMC were negative for gp51 antigen expression, but 11 cattle were positive following short-term culture of their PBMC; 10 of these were seropositive/provirus-positive cattle, and one was a seropositive/provirus-negative cow. Lymphocytosis was present in eight cattle, all of which were seropositive/provirus-positive/gp51-positive. Four cattle were provirus-positive, but negative for all other indicators of BLV infection; a second blood sample was collected from three of these cattle at a later date, at which time two of the three had seroconverted. These results suggest that depending on the stage of the infection, the pathogenesis of BLV in cattle may involve fundamental differences in the host-viral relationship, including the number of cells infected or the number of copies of integrated provirus per cell, regulation of expression of viral antigens, induction of the anti-viral immune response, and the polyclonal or monoclonal proliferation of lymphocytes.

In vitro expression of bovine leukemia virus in isolated B-lymphocytes of cattle and sheep

The purpose of this study was to determine the effect of T-lymphocytes and phytohemagglutinin (PHA), a T-cell mitogen, on the expression of bovine leukemia virus (BLV) in cultured B-lymphocytes from BLV-infected cattle and sheep. Bovine B-lymphocytes were isolated by negative selection via complement-mediated lysis of T-lymphocytes. Additionally, bovine and ovine B-lymphocytes were positively selected using fluorescence activated cell sorting. Expression of BLV in cultured bovine and ovine B-lymphocytes occurred in the absence of T-lymphocytes and without PHA stimulation. The results of this study demonstrate that BLV replication in cultured B-lymphocytes is T-cell independent. This finding may have implications for the mechanism of viral latency within infected B-lymphocytes.

Prospective characterization of the clinicopathologic and immunologic features of an immunodeficiency syndrome affecting juvenile llamas

The clinicopathologic and immunologic features of 15 llamas affected with juvenile llama immunodeficiency syndrome (JLIDS) are described. Healthy adult (n = 10) and juvenile (n = 10) llamas served as controls. JLIDS llamas were characterized by wasting, and clinically apparent, repeated infections were frequently observed. The median age at which a health problem was first perceived was 11.6 months. All 15 affected llamas died or were killed, and JLIDS was confirmed at necropsy. The median duration of illness was 3.5 months. Lymphocyte blastogenesis assays showed suppressed responses (particularly to Staphylococcus sp. Protein A) in JLIDS llamas. No evidence of retroviral infection was detected. Mild, normocytic, normochromic, non-regenerative anemia, low serum albumin concentration and low to low-normal globulin concentrations were typically found on initial clinical evaluation. Lymph node biopsies showed areas of paracortical depletion. All llamas affected with JLIDS had low serum IgG concentrations, pre-vaccination titers against Clostridium perfringens C and D toxoids of < or = 1:100, and no titer increase following vaccination.

Cytoplasmic fragmentation associated with lymphoid leukemia in ruminants: interference with electronic determination of platelet concentration.

Leukocyte cytoplasmic fragmentation is associated with human leukemia, usually with leukocyte concentrations in excess of 1 O0,000/J.1.2.4,6 Increased attention has been drawn to leukocyte cytoplasmic fragments with the common use of automated hematology analyzers, and the recognition that such fragments interfere with the whole blood platelet counting capability of these instruments and by microscopy on hemocytometers. 1.2.4.6 This report documents interference of prominent leukemia-associated leukocyte fragmentation with automated electronic determination of platelet concentration in a cow and a sheep. This observation is important in veterinary hematology because it represents a morphologic feature of leukemia in animals and may result in errant enumeration of platelets by a variety of techniques. The S-Plus series of automated blood cell counters determines blood platelet concentration by mathematical analysis of both particle size distribution and concentration within a size range window encompassing approximately the lower third ofthe potential platelet volume range. This size window is about 1.3-1 3 fl on most automated cell counters modified for use in veterinary hematology. The instrument calculates platelet concentration after fitting a log normal curve to raw data in the size window (Fig. IA). In order for the curve fitting routine to function it must detect one mode between two minimum points within the size window. Furthermore, the mode must be between 2 fl and 10 fl on the modified system. If any of these criteria are not met, curve fitting is not done, an incomplete computation occurs, and platelet concentration is not printed. A cow and a sheep were evaluated hematologically by examination of Wright-Giemsa-stained blood films and an automated hemogram. Hemograms were done on an automated multi-channel analyzer modified for use in veterinary hematology by increasing the erythrocyte-platelet aperture bath current to 225 V (Coulter Counter Model S-Plus IV with histogram capability, Coulter Electronics Inc., Hialeah, FL). Platelet adequacy was estimated by blood film examination: no attempt was made to enumerate platelets by hemocytometer. The sheep was a 13-month-old black face ewe, which had been inoculated experimentally at 3 weeks of age with bovine leukemia virus (BLV) and was BLV-seropositive. Hematologic evaluation revealed severe nonregenerative anemia (hematocrit = 0.13) and extreme leukocytosis. The blood was diluted 1 : 10 to determine the leukocyte concentration. The total leukocyte concentration was 699,00O/pl, with 100°/o lymphoblasts. The sheep was killed for necropsy and was found to have multicentric lymphosarcoma consistent with that described following experimental infection with BLV.5 A 7-year-old Holstein cow suspected to have a displaced abomasum was brought to the Colorado State University. Masses were present in regions of the thoracic inlet, supra177