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The development of the antibody concentration against lipopolysaccharide (LPS) of S. Typhimurium und S. Choleraesuis in rearing pigs during the fattening period and in breeding sows of the corresponding age was recorded. The studies revealed the following results. Antibodies of isotypes IgG1 and IgG2 revealed a more pronounced specificity against the according Salmonella serovar than IgM antibodies. The calculated "antibody percent value" based on the total amount of Salmonella antibodies is mainly determined by the IgM antibodies in sera and meat juice, respectively. In fattening pigs a significant increase of antibodies against IgM and total Ig was observed between week 3 and 10 after beginning of the rearing period. In breeding pigs this increase was detectable already earlier. In only 3 out of 10 groups an increase of IgG1 and IgG2 was also seen. The detected significant increase of total Ig and IgM in the other groups might be the result of a less intensive exposure to salmonellas or it might be due to an increase of unspecific antibodies induced by other antigens. Serological investigations represent a valuable tool to record the intensity and development in time of the Salmonella exposure in pigs farms. Examination of total Ig is an appropriate method to detect pig herds with a high level of Salmonella exposure, for detailed epidemiological studies in pig farms the examination of antibody isotypes will give more comprehensive information.

Using the close linear regression between the logarithm of the dilution degree of a sample and the logarithm of the extinction measured in an ELISA both the relative concentrations of immunoglobulines of the isotypes IgG, IgM and IgA and of the LPS antibodies against S. Typhimurium of the different isotypes in blood sera and meat juice of 15 slaughtered pigs were detected and compared. Furthermore the total concentration of antibodies against LPS of S. Typhimurium according to the "meat juice ELISA" were compared. Distribution of immunoglobulines between serum and meat juice revealed individual differences between the animals as well as between the different immunoglobulin-isotypes. Within the same isotype the ratio of the concentrations of anti-LPS Salmonella Typhimurium antibodies between serum and meat juice was significantly closer than relating the whole of immunoglobulines of the referred isotype. In order to detect pig herds with a high level of Salmonella exposure a comparison of the 1:30 diluted meat juice samples with the 1:400 diluted blood sera is justified, however, for detailed epidemiological or scientific studies there is a need to consider the existing differences between the immunoglobuline-isotypes as well as between the specificity of antibodies and of total immunoglobulines. While the concentration of Salmonella antibodies of the isotypes IgG1, IgG2 and IgA showed a clear and statistically significant correlation between both one below the other and with the total amount of Salmonella antibodies, this connection could not be established for the total amount of immunoglobulines of different isotypes and the IgM-antibodies.

LPS antibody reaction of S. Typhimurium was detected in a total of 111 two- to ten-week-old pigs, which had been exposed to experimental oral infection with this serovar in 16 separate experiments. The total antibody level was determined according to the meat juice ELISA provided for the Salmonella control programme and the antibody concentrations of the isotopes IgG1, IgG2, IgA and IgM. Although there were significant differences between the individual experiments with respect to the reaction intensity and proportion of the individual immune globulin isotypes, the following general statements on the dynamics of the antibody reaction can be made: Clearly elevated antibody levels could be observed one week after the onset of infection. After one and two weeks, respectively, 22.5 and 52.9% of the infected animals showed antibody levels which were to be evaluated as positive in the sense of the Salmonella control programme (> or = 40%). While the concentration of the IgM-related antibodies decreased again during the second week already, the antibody concentration of IgG1 and IgG2 continued to increase until the end of the experiment after 3 weeks. The clear differences in the reactions between the experiments cannot be explained solely by defined conditions of infection such as strain of infection, infective dose or age of the pigs. Obviously, other non-defined or non-recognized factors may have a decisive influence on the dynamics of the antibody reaction in the animal groups.

Information about the proportion of truly Salmonella-free herds is required for an evaluation of the epidemiological situation, the development of control strategies and their implementation. Findings regarding the presence of salmonellas in faeces and intestinal lymph nodes as well as the presence of Salmonella antibodies in meat juice from slaughtered pigs were obtained in the context of a study conducted by a number of institutes. These data were used for an analysis of the validity of data on the prevalence of infected animals within herds and on the prevalence of infected herds. The proportion of batches or herds with exclusively negative individual findings was found to depend not only on the true proportion of truly Salmonella-free animals within herds but quite essentially also on the distribution of the proportion of infected animals within herds, the sensitivity of the methods of examination and sample sizes. When taking into account the existing dependencies, it was found that among the swine, the real numbers of Salmonella carriers were much higher than shown by bacteriological and serological examination. Regarding salmonellosis in swine, also a number of contaminated herds must be expected which is far higher than that shown by the number of herds with positive findings in at least one animal. Even a low contamination of all or almost all herds would result in the numbers of 'negative' batches observed, i.e. batches with exclusively negative individual findings. A rating of the salmonella exposure of herds as high, low, or very low is possible and may, and should be, used for measures of consumer protection, irrespective of the proportion of truly Salmonella-free herds.

Hybrid swine (Landrace x Pietrain) aged 3-4 weeks were immunized twice at an interval of 3 weeks solely by the oral route and by the oral/parenteral route to evaluate the efficacy of a live S. Typhimurium vaccine. In each experiment a control group was run without vaccination. The animals were challenged at the age of 8-10 weeks by oral test infection with a labelled S. Typhimurium DT 104 strain. An ELISA was used to establish the presence of antibodies to S. Typhimurium in serum samples, coupled with clinical investigation. The presence of the challenge strain in the ileal and caecal mucosa and in the ileocolic lymph nodes was investigated quantitatively using the Koch plating method to determine the degree of colonization of those organs at the time of slaughter. The clinical course of disease was used to assess the success of vaccination. However, it was not possible to trigger, in a reproducible manner, clinical signs of disease in unvaccinated animals through infection. The vaccinated animals had a significantly lower (p < 0.05) colonization of the ileal and caecal mucosa than the unvaccinated animals. This was also seen to a lesser degree for the ileocolic lymph nodes.

Programmes for controlling salmonella infections in German piggeries are based on the meat-juice-ELISA conducted in various investigation centres by using different test-kits. A usual procedure for harmonization (standardisation) of results is the calculation of the percentage of antibody-concentration from field samples in relation to the extinctions of a set of control-sera with known antibody concentrations. Whether this system is still acceptable in case of using different test-kits seems to be questionable. In principle, difficulties arise by calculating field results from the regression curve of control-sera because the calculated percentages of antibodies do not represent the antibody concentration but, instead, the percentages of the extinctions measured, and secondly, because control-sera presently in use are directed against different salmonella serovars. In regard to the number of laboratories involved and because of a variety of test-kits used it seems to be more adequate to include only one anti-Salmonella Typhimurium standard-serum at a given antibody concentration which is to be tested repeatedly on every test-plate. Simultaneously, further controls should include another anti-Salmonella Typhimurium and one anti-Salmonella Choleraesuis serum which should provide results similar to the Danish system which is regarded as a standard. As well, a negative serum must be included in the test and a minimum difference in extinctions between this negative serum and the standard positive control-serum should be reached to prove the validity of results from the test plate.

According to the test protocol of the "meat juice ELISA" for detection of salmonella antibodies in pigs, all meat juice samples and serum controls are to be tested in duplicate. Results from routine investigations of repeatedly double tested meat juice and serum samples have been used to analyze the effect of double testing versus single testing with regard to the reliability of the final result. In case of an individual animal, testing of samples in duplicate increases the reliability of the results significantly, especially, if samples are retested at different occasions. In contrast, such a difference between mono and double testing of samples is not of importance when a group of animals is tested in order to determine the mean antibody rate in a herd. Here, results from double testing practically do not contribute to a higher reliability of the final result. This observation provides the possibility to reduce the costs for investigation programmes drastically.

Distribution of maternally transmitted Salmonella antibodies and their protective effects were studied in the progeny of broiler breeder birds which had been vaccinated with live S. Typhimurium and inactivated S. Enteritidis vaccines. Vaccination resulted in a significant increase of the antibody concentration in yolk of hatching eggs and in serum and jejunum of the progeny of immunized breeder birds. Higher antibody titres for isotypes IgG and IgA were still seen on day 21 of age. Antibody production of isotypes IgA and IgM by the chickens themselves was found between 14 and 21 days of age. Two challenge models (10(2) cfu/bird on day 1 of age and a seeder bird model, respectively) were used to evaluate the efficacy of maternal antibodies against challenge with S. Enteritidis. Using both models numbers of challenge organisms were lower in the caeca of the progeny of immunized parent birds between day 7 and day 21 of age (maximum about 1.5 log10 units) compared with control chicks. The results indicate the efficacy of maternally transferred antibodies but it remains the question of their practical relevance. The effects of acquired maternal antibodies on an active immunization of the progeny of immunized breeder birds with live Salmonella vaccines are discussed.

Among cattle sera from herds without a history of salmonellosis and without vaccination against salmonellas, we sometimes found samples which reacted positively in the ELISA with salmonella antigen. Contrary to antibodies caused by a proved salmonella infection, these antibodies could be eliminated by a whole-cell lysate of E. coli. In the colostra of cows which had received a salmonella live vaccine orally in the first days of life but were raised and kept without known exposition to salmonellas, we also found antibodies which reacted in the salmonella ELISA. They could not be eliminated by E. coli lysate.

5 groups of five calves each were orally infected with the salmonella serovar S. agona, S. dublin, S. enteritidis, S. infantis or S. typhimurium. The course of infection and the humoral immune response against 5 antigen preparations of the homologous and the 4 heterologous salmonella serovars were monitored in each group. Antibodies against two different protein antigens and against two differently prepared LPS antigens were determined by ELISA and the level of H-agglutinin was assessed by micro agglutination test. All 5 serovars proved to be virulent for calves. The specificity of antibodies produced following the infection are not always consistent with the Kauffmann-White scheme. There was a relation of age and strain for infection on immune response, whereas the severity of infection did no correlate with an increase of antibody production. The serological tests used were good for investigation of a defined host-parasite-interaction but not satisfactory for serovar specific diagnosis of salmonella infection in cattle.