Veterinary medicine, food security and the global environment.

The authors focus on the role of veterinary medicine in feeding the nine billion people projected to inhabit the planet by 2050, despite the problems of global warming, political constraints and environmental destruction. Population growth, predominantly urban, will occur mainly in developing countries, at a magnitude comparable to creating a city the size of Los Angeles, the second largest city in the United States of America, every three weeks for the next 40 years. Accompanying this growth will be a greatly increased demand for animal protein. How this burgeoning demand can be met by intensive and extensive systems of animal production is discussed, with particular reference to the immensely important role that the veterinary profession and schools must play.

Transmission of human T cell leukemia virus type I to sheep: antibody profile and detection of viral DNA sequences.

Lambs were inoculated intraperitoneally with either 1.8 x 10(7) live peripheral blood cells from an HTLV-I-infected person (five lambs) or with 8 x 10(7) live cells from the HTLV-I-producing cell lines MT-2 (four lambs) or C10 MJ (five lambs). Four control lambs were inoculated with minimal essential medium supplemented with fetal calf serum. The animals were monitored during a period of 24 months. Beginning at 5 to 12 months after inoculation, four of the five lambs inoculated with the fresh HTLV-I-infected peripheral blood cells began to develop detectable levels of antibodies to a recombinant HTLV-I gp21env antigen, as determined by an enzyme-linked immunoassay (ELISA). The anti-gp21 antibodies persisted for the remaining observation period. These antibodies were not detected in the sera from the other sheep. Absorption and blocking experiments demonstrated the specificity of the gp21 reactivity. This reactivity was also confirmed by Western blot (WB). With the exception of the serum of an MT-2-inoculated sheep that formed a weak band with p19 by WB, none of the sera of the four gp21-positive sheep or of the other experimental sheep reacted with other structural or regulatory HTLV-I proteins, as determined by ELISA, WB, and radioimmunoassay. PCR analyses demonstrated the presence of the HTLV-I provirus in peripheral blood leukocytes of the four sheep showing antibodies to gp21env. The remaining sheep were negative. PCR analyses failed to detect BLV sequences in any of the experimental sheep. None of the sheep showed clinical abnormalities during the observation period. The potential value of the sheep model for studying atypical virus-host interactions in infected people is discussed.

Persistent lymphocytosis in cattle: its cause, nature and relation to lymphosarcoma.

Studies in well-characterized cattle populations strongly support the view that the bovine leukemia virus (BLV) is the causative agent of the adult (enzootic) form of bovine lymphosarcoma and persistent lymphocytosis (PL), and that host genetic factors play an important role in the development of these two conditions. On the other hand, the available information indicates that the genetic factors controlling the development of PL are frequently independent of those controlling the development of lymphosarcoma. There is no evidence that clinically normal cattle with PL harbor malignant cells or have any other clinical abnormality. In these animals lymphocytosis results from the expansion of two distinct subpopulations of non-neoplastic B lymphocytes, one of which is free of BLV. Long-term studies have shown that the large majority of cattle with PL do not develop lymphosarcoma even when kept to advanced age. These data indicate that PL is not a disease nor a preclinical stage of lymphosarcoma. Rather PL should be considered as a benign response to BLV infection which, although frequently associated with lymphosarcoma, is independant of it.

Cytogenetic, cytological, and virological characteristics of a bovine fibrosarcoma.

The features of a bovine tumor with typical histopathological characteristics of a malignant fibrosarcoma are described. Direct karyotype preparations from the tumor tissue showed two populations of cells with bizarre karyotypes. An in vitro cell culture, designated BS-2, derived from the tumor had a normal diploid karyotype. This culture formed syncytia and produced a virus morphologically indistinguishable from the ubiquitous bovine syncytial virus. BS-2 cells reacted strongly in immunofluorescent tests with both bovine syncytial virus reference serum and serum from the tumorous cow. The virus was also demonstrated by immunofluorescence and mixed culture techniques in the buffy coat cells of the same cow.

Seroepidemiological evidence for horizontal transmission of bovine C-type virus.

Thirty colostrum-deprived calves from leukemia-free herds were foster nursed for 10 weeks on cows infected with bovine C-type virus (BLV) from multiple-case herds or on cows from leukemia-free herds. After weaning, the calves were raised in continuous contact with BLV-infected animals of approximately the same ages. Sera collected at 6 to 18 and 43 to 48 months of age were examined for the presence of antibodies to BLV by the immunofluorescent antibody test. At 6 to 18 months of age, only 1 of the 30 calves from leukemia-free herds had a detectable antibody response to BLV. By 43 to 48 months of age the number of antibody-positive animals had risen to 17. The foster dam's herd of origin did not significantly affect the rate of BLV infection. These results indicate that BLV can be horizontally transmitted from infected to noninfected animals.

Serological diagnosis of infection with the putative bovine leukemia virus.

We report on an accurate, rapid and inexpensive test for the identification of animals infected with the Bovine C-type virus (BLV). The test involves the detection of serum antibodies to BLV using the immunofluorescent (IF) technique on acetone-fixed, infected cells. The specificity of the test was demonstrated by the fact that virus was found by electron microscopy in 90% of cattle showing positive reactions. In contrast, virus was not found despite extensive examination in antibody negative animals. Thus, the presence of IF antibody is an accurate indicator of current rather than past BLV infection. In order for the IF test to be specific it is of critical importance that the target cells used are infected only with BLV. BLV antibodies can also be detected by the immunoprecipitation (Ouchterlony) technique. However, a significant proportion of BLV infected animals showing positive reactions in the IF test failed to show precipitin antibodies to the virus. Likewise, BLV infection was demonstrated by both the IF test and electron microscopy in many animals with persistently normal levels of blood lymphocytes. Thus, neither the precipitin test nor the blood lymphocyte count (Bendixen's key) can be used to rule out BLV infection.

Further studies on the antigenic properties and distribution of the putative bovine leukemia virus.

The C-type viruses found in long-term cultures. New Bolton Center (NBC) cell lines, of peripheral lymphocytes from leukemic cattle and in short-term cultures of bovine buffy coat(BC) cells share an immunofluorescent(IF)antigen detected in the cytoplasm of infected cells as well as an antigen demonstrable in gel diffusion experiments. Therefore the viruses from these cultures most likely represent different isolates of the putative bovine leukemia virus (BLV). The BLV precipitin antigen is analogous to the group specific (gs) antigens of the leukemia viruses of other species in that it is soluble, ether resistant, and apparently located within the virion. These observations, together with results showing that the specificity of the BLV precipitin antigen differs from that of the gs antigen of other mammalian leukemia viruses, indicate that the former antigen represents the intraspecies (gs-1) determinant of BLV. Antibodies to the precipitin viral antigen were found in 82% of cattle with leukemia and in 40% of clinically normal adult cattle in multiple-case herds. These groups of animals also had fluorescent antibodies to the virus, but with significantly higher frequencies (100% and 76%, respectively). On the other hand, in leukemia-free herds, precipitating antibodies were not found and the incidence of fluorescent antibodies was only 3%.