Bovine brucellosis: an investigation of latency in progeny of culture-positive cows.

Calves (n = 150) born to cows infected with field strains of Brucella abortus were weaned within 24 hours after birth or allowed to nurse until weaned (age at weaning ranged from 10 to 43 weeks). After weaning, female calves were placed in small groups in special pens constructed to prevent further direct and environmental exposure to brucellae. At weaning, male calves were moved to an isolated pasture and were kept as a single group. Later, first-generation heifers were bred and placed in individual isolation pens until termination of pregnancy. Two of the first-generation heifers (that were culture-negative) developed persistent serologic responses (to B abortus) of unexplained origin. Brucellae were not isolated from progeny of infected cows (105) or from progeny offspring (95 fetuses and neonates), indicating that latency may be infrequent.

Leptospiral and brucellar titers in frozen bovine sera after 20 years of storage.

Generally good agreement was obtained between the rankings of sera titers when originally tested (T1), and those of the same sera 20 years later (T2). At the later time, the majority of samples (88%) were in, or within 1 dilution factor of their classification at T1. Test results for Brucella abortus and Leptospira interrogans var pomona antibodies demonstrated that original titers, in the upper-lower limits of 20 to 50, had decreased over a wide range (20% to 90%), and the later tests show that the greater the original titer, the greater the proportional decrease. Thus, titers of 20,000 at T1 had decreased by 49% to 99% and those of 200,000, by 95% to 99.8%. Variations in T2 test results were noted between some samples which had given identical results at T1. A decrease in titer over time has been demonstrated. An estimate of the expected half-lives of sera of differing initial Leptospira antibody titers is that for each unit increase in log10 of the initial titer, the half-life is reduced by about 50%. The heterogeneity of the immune response is postulated as the reason for this variation.

Safety aspects in preparing suspensions of field strains of Brucella abortus for serological identification.

Forty field strains of Brucella abortus, obtained from milk and vaginal samples of naturally infected cattle, were heated in a waterbath at 65 degrees C, 75 degrees C, 80 degrees C for 60 to 120 minutes. Ninety-five per cent survived 65 degrees C for 120 minutes, 55 per cent survived 75 degrees C for 120 minutes, 25 per cent survived 80 degrees C for 120 minutes and 12.5 per cent survived 85 degrees C for 60 minutes. No isolates survived 85 degrees C for 75 minutes.

Studies on in vitro lymphocyte stimulation assay in cattle naturally infected with Brucella abortus and in cattle vaccinated with strain 19.

Cell-mediated immune responses of cattle in infected herds vaccinated with Brucella abortus, strain 19, and of nonexposed controls were studied by an in vitro lymphocyte stimulation test (LST). Brucella abortus soluble antigen was used as a specific stimulator of lymphocytes. Lymphocyte suspensions were prepared from peripheral blood of cattle by the Ficoll-diatrizoate technique. Cultures were labeled with [3H]thymidine and were assayed for [3H]thymidine incorporation into DNA by liquid scintillation spectrometry. Seroagglutination tests and cultures from Brucella were conducted simultaneously with LST. Brucella abortus soluble antigen induced significantly higher (P less than or equal to 0.005) lymphocyte stimulation responses in lymphocytes from cattle infected with B abortus than in lymphocytes from cattle vaccinated with strain 19 or from nonexposed controls. There was a significant P = agreement in results of LST and seroagglutination tests in infected cattle. Among seropositive-vaccinated cattle and controls, the LST was negative.

Cell-mediated immune response after Brucella abortus S19 vaccination.

Cell-mediated immunity to Brucella abortus S19 vaccine was measured in young heifers by the microassay for stimulation of protein synthesis (SPS) with [3H]leucine and the skin test for delayed hypersensitivity. Brucella melitensis protein allergen and a crude B abortus S19-soluble antigen were compared in the SPS test. The SPS test was negative in 5 unvaccinated heifers and strongly positive in 3 twice-vaccinated steers. However, the SPS test was positive only in 13 of 30 S19-vaccinated heifers and the delayed hypersensitivity in 9 of 29 S19-vaccinated heifers. The 2 tests gave good agreement. Vaccination-induced residual antibody titers were partly correlated with the outcome of the tests used to measure cell-mediated immunity.

The relationship of erythrocyte age and parasitization with Plasmodium gallinaceum in chickens.

Erythrocyte labeling by random and cohort techniques was used to study erythrocyte survival in normal chickens and in chickens infected with Plasmodium gallinaceum. White Leghorn chickens, eight weeks of age, were used in this series of experiments. In chickens given P. gallinaceum on the day following erythrocyte labeling there was destruction of labeled erythrocytes at a much more rapid rate than would result from normal ageing processes. Chickens given P. gallinaceum 12, 18 and 21 days after the labeling of the erythrocytes failed to show any greater destruction of the labeled red cells beyond that resulting from normal senescence. This result indicates that erythrocytes over 12 days of age are not destroyed by P. gallinaceum.