[The problem of recurrence of enzootic bovine leukosis in previously cured herds]. / Das Problem des Wiederauftretens der enzootischen Rinderleukose in zuvor sanierten Beständen.

Within nine months, enzootic bovine leukosis (EBL) occurred in 23 well documented herds. Eight of them (= 35%) had previously conducted the eradication programme as laid down by law. This proportion is tenfold higher than anticipated from the average incidence rate since 1978. The conclusion is drawn that a higher risk for reinfection exists for herds previously infected and cleaned than for those that never had leukosis before. For such cases hypotheses are presented. In one case clear evidence for one of the hypotheses was obtained. In case of re-occurrence of EBL in a previously cleaned herd it is proposed to examine the white blood picture of the sero-positive animals. If hematologically positive cattle are detected, they should be removed from the herd including their offspring.

Enzyme-linked immunosorbent assay for detection of bluetongue virus antibodies.

The immune response to bluetongue virus in sheep and cattle was studied by applying a newly developed indirect enzyme-linked immunosorbent assay (ELISA). Purified virus obtained by sucrose gradient centrifugation was used at a concentration of 0.01 optical density units (formula: see text) to coat individual wells (200 microliter) of a microtitration plate. Dilution of antigen was performed in 0.05 M carbonate buffer, pH 9.6, and adsorption lasted for at least 16 hours at 4 C. Coated plates retained their activity for 10 weeks when stored at 4 C. Sera recovered from experimentally infected sheep and cattle were tested together with known negative sera. A good correlation between results was obtained with the modified complement-fixation test and the ELISA; however, the ELISA proved to be more sensitive. The group specificity of the ELISA was proven by testing various type-specific sheep and cattle immune sera. The ELISA has potential for the detection of group-specific antibodies to bluetongue virus infection.

Some observations on the epidemiology of bovine leucosis virus infection in a large dairy herd.

Bovine leucosis infection rates were calculated for two years in a naturally infected dairy herd in which serologically positive animals were not preferentially culled. Transmission of infection was found to occur mainly during the winter housing period. No variation in susceptibility to infection with age was found and young animals did not show a prolonged time from infection to sero-conversion.

Testing the mutagenic potency of chemical substances in a linear host-mediated assay (LIHMA).

Instead of comparing "mutation frequencies" as used in the conventional host-mediated assay (HMA), a modified concept of measuring mutagenic potency is introduced by using a number of time intervals for taking samples. Regression analysis methods can then be applied to the numbers of mutant bacteria (reversions). Not only the mutagenic but also an additional antibacterial potency of a compound can be detected and estimated in the sam assay. It is demonstrated that interference of (undetected) antibacterial activity with the mutagenic activity may lead to misclassification of a substance concening its mutagenicity in the conventional HMA. This kind of erroneous assessment will be avoided by the LIHMA. Another advantage of the LIHMA over the conventiona HMA is that regression analysis also allows estimation of the sensitivity and reliability of the assay. The calculative procedure may be programmed on desk computers and is then most suitable for laboratories where large numbers of substances have to be examined routinely. A numerical is given using results obtained with nitrosoguanidine.

[The propagation of swine fever virus in cultures of macrophages and lymphocytes of normal and immune pigs (author's transl)]. / Untersuchungen zur Vermehrung des Virus der Europäischen Schweinepest in Makrophagen- und Lymphozyten-Kulturen von normalen und immunen Tieren

Swine fever virus is replicated in the cells of the lymphoid complex. During the course of the disease cell-destruction, leucopenia and a disturbance of globulin and transferrin production is described. In the case of recovering firstly the leucocyte population, specially the lymphocytes, later on antibody titer increase. The production of virus neutralizing antibodies is not recognizable to be the cause of a recovery, the latter seems to be initiated by the production of a newly formed cell population. Therefore macrophages and lymphocytes of normal and of swine fever immune pigs are compared respecting the virus replication in vitro. Hereby macrophage cultures did not show any differences. In contrast to these findings in the tissue cultures consisting of predominantly lymphocytes of normal animals the virus replication exceeded that of immune pigs. Further on in the lymphatic organs of pigs killed in the recovering state newly formed clones of lymphoid cells were detected, which did not show swine fever specific but a globulin specific fluorescence. Obviously during the reconvalescent state a population of immune relevant lymphocytes is being created, which is different of these of non-immune pigs, since swine fever virus is not propagated by them anymore.

[Studies on the Relationship between immunity and the level of neutralizing antibodies in pigs vaccinated against foot-and-mouth disease (author's transl)]. / Untersuchungen zur Abhängigkeit zwischen immunität und Höhe der Neutralisationstiter bei Schweinen nach Impfung mit Maul- und Klauenseuche-(MKS-)Vakzinen

The statistical relationship between the titers of neutralizing antibodies and the immunity of 706 pigs vaccinated against FMD was studied. This was done for each of four virus strains separately. Whereas no correlation between both test systems could be detected in case of the strains A5 Westerwald, C Detmold and O1Santander, a significant correlation was ascertained for the strain O1Kaufbeuren. Becuase of the different findings depending on the virus strain under study it was concluded that the antibody titer alone does not provide a useful measure for potency testing of FMD-vaccines for pigs.