Genetically altered stable nonreverting aromatic-dependent (aro-) Salmonella dublin, strain SL5631, was administered orally to healthy colostrum-fed calves as vaccine. Twenty-six calves were allotted to 4 groups. There were 2 experiments, each with a vaccinated and nonvaccinated control group. Skin testing with 0.1 ml of sonicated S. dublin was performed 3 days prior to challenge exposure. The IgG and IgM titers to S. dublin lipopolysaccharide (LPS) antigen were determined by ELISA on sera before initial vaccination and at 1.5 to 2 weeks after each vaccination. In experiment 1, six calves received a dose of 1.7 X 10(10) colony-forming units (CFU) of aro(-) S. dublin SL5631 orally at 2 and 4 weeks of age. After the first vaccination, 2 of 6 calves developed fever, but all 6 calves continued to have normal appetite and mental attitude. Adverse changes were not observed after the second vaccination. At the time of challenge exposure at 6 weeks of age, all 12 calves were seronegative for IgG and IgM LPS-specific antibodies, and the difference in percentage increase in skin test reaction at 48 hours was not significant. At 6 weeks of age, the 6 vaccinates and 6 controls were orally challenge-exposed with 1.5 X 10(11) CFU of virulent S. dublin T2340. Protection from challenge was not evident, as 3 of 6 controls and 5 of 6 vaccinates died after challenge exposure. In experiment 2, eight calves received a dose of 5 X 10(11) CFU of aro(-)S dublin SL5631 orally at 2, 3.5, and 5 weeks of age. The vaccine dose and volume (300 ml) were 30 times that of experiment 1. After each vaccination, some calves (7, 6, and 2 calves for first, second, and third doses, respectively) developed fever, but all calves continued to have normal appetite and attitude. At 7 weeks of age, the 8 vaccinates and 6 controls were orally challenge-exposed with 1.5 X 10(11) CFU of virulent S. dublin T2340 (same dose as experiment 1).

Live, avirulent Escherichia coli vaccine strains were constructed and tested for efficacy in preventing colibacillosis in 4-week-old pigs. Either or both of 2 plasmids were inserted into avirulent E coli strain G58-1 (0101:NM). These plasmids were pPMC4, which encodes for LTb subunits of heat-labile enterotoxin, and pDHF1, which encodes for K88ac fimbriae. Litter- and weight-matched pigs were removed from sows when they were 10 days old and vaccinated orally with the constructed strains or with G58-1 (negative control vaccine) when they were 2 weeks old and 5 days later. All pigs were challenge-inoculated with virulent E coli strain 3030-2 (0157:K88, LT+, STb+) 2 weeks after the first vaccination. Only 1 pig vaccinated with G58-1/pPMC4/pDHF1 developed diarrhea and none died following challenge inoculation. Seventeen of 31 control pigs developed diarrhea and 11 died. Of 18 pigs vaccinated with G58-1/pDHF1 then challenge-inoculated with the virulent strain, 5 developed diarrhea and 2 died. Fifteen of 18 litter- and weight-matched controls developed diarrhea and 8 died. When compared with G58-1 (negative control), G58-1/pPMC4 afforded no protection to pigs challenge-inoculated with 3030-2.

Classical swine fever virus (CSFV) causes an economically important and highly contagious disease of pigs, leading to economic losses around the world. Attenuated live vaccines with CSFV antigens have played an important role in the prevention and control of the disease. Porcine kidney 15 (PK15) cells have been widely used for the propagation of CSFV, but this cell line is not efficient or homogeneously susceptible to viral infection. To achieve a homogeneous PK15 cell line which enabled high titre replication of CSFV, we used the limiting dilution cell cloning method. We developed two cell clones, PK15-1A6 and PK15-3B1, which respectively have high- and low-permissive phenotypes to CSFV infection. The PK15-1A6, PK15-3B1, and PK15 parent cells showed different characteristics in cell proliferation rate, susceptibility to CSFV infection, and CSFV production. The mean virus titres per millilitre reflected by TCID₅₀ values in PK15-1A6, PK15-3B1, and PK15 parent cells were 106.85, 103.63, and 104.74, respectively. The PK15-1A6 cell clone is more permissive to CSFV infection than the PK15 parent cells. The screened high-permissive cells will be useful for CSFV propagation and vaccine development in vitro, and facilitate research on the pathogenicity of CSFV.

To develop a live vaccine candidate using an attenuated strain of Salmonella Typhimurium (ST), biochemical properties, plasmid profile, PFGE patterns and pathogenic analysis of the ST isolate were carried out after sequential passage of the ST isolate in porcine neutrophils. By the passage, the ability of the neutrophil-adapted isolate to utilize d-xylose was lost, while the ability of the strain to ferment trehalose was delayed after 2 or more days of the culture. Also, changes including deletion of the gene fragments were observed in PFGE analysis of the neutrophil-adapted isolates. Two plasmids, 105kb and 50kb, were cured in the strain passaged over 15 times in porcine neutrophils. The 50% of lethal dose (LD50) of the parent strain was changed from 1 × 105 LD50 to 6 × 106 LD50 by the passage in intraperitoneal injection of the strains into mice. These results suggested that bacterial genotypic and phenotypic responses might be globally altered depending on the inside environment of neutrophils.

An attenuated vaccine strain AVR1/08 of Korean respiratory type of infectious bronchitis virus (IBV) was developed by 89th passages of IBV D85/06 strain in chicken eggs. The AVR1/08 strain had higher virus titer at least 20 times (10∨1.3) than the parent virus D85/06 by egg inoculation method. The AVR1/08 strain had a single point mutation (S to Y) at position 56 of spike protein of IBV compared to parent virus IBV D85/06 strain. The mutation was observed consistently at viruses after 47th passage in chicken eggs. The AVR1/08 strain showed no virulence even after 6 passages in chickens and all chickens inoculated induced anti-IBV antibody 14 days after vaccination. The AVR1/08 strain had broad protective efficacy against QX type Korean nephropathogenic virus (Q43/06 strain), KM91 type Korean nephropathogenic virus (KM91 strain) and Korean respiratory virus (D85/06 strain). In contrast, Massachusetts (Mass) type attenuated vaccine strain H120 showed protection of 37.5 to 50% against these three viruses. Our results indicate that the AVR1/08 strain has potential as an attenuated vaccine effective in controlling IBVs circulating in Korea.

An avirulent live Salmonella choleraesuis culture (SC-54) was evaluated for use as an effective vaccine in preventing salmonellosis caused by S choleraesuis in pigs. Eighty-two pigs, 3 to 4 weeks old, were randomly assigned to 1 of 2 treatment groups, which were designated as either vaccinates or controls. After vaccination, all pigs were examined for fecal shedding of S choleraesuis, rectal temperature, and 10 clinical variables. Significant difference was not detected between vaccinated and nonvaccinated pigs for 14 days (phase I) after intranasal administration of the vaccine. Efficacy and duration of immunity were examined by intranasally challenge exposing respective pigs from either treatment group with a virulent field isolate of S choleraesuis at 2, 8, or 20 weeks after vaccination (phases II-IV). Pigs were again evaluated for 14 days after challenge exposure, and 10 clinical variables and rectal temperature were monitored. Surviving pigs were euthanatized and evaluated for gross lesions, and samples of 7 organs were collected. These organ samples were homogenized, and level of S choleraesuis infection was determined. After virulent challenge exposure during phases II-IV, the clinical status of the SC-54 vaccinates was significantly (P < 0.05) superior to that of nonvaccinates for rectal temperature, feces consistency, behavior, appetite, body condition, and mean score for the 10 clinical variables. Quantitative bacteriologic culture of the tonsil, lung, liver, spleen, mesenteric lymph nodes, ileum, and colon samples indicated consistent reduction of organ colonization in vaccinates; bacteria numbers in the mesenteric lymph nodes, lungs, and ileum were significantly (P < 0.05) reduced. Gross lesions in pigs indicated reduction of pneumonia in vaccinates. Pigs also had consistent weight gain throughout all phases of the study after challenge exposure, although the differences were not significant. In conclusion, a single intranasally administered dose of SC-54 given to 3- to 4-week-old pigs proved to be safe and efficacious and to provide protection to pigs at least 20 weeks after initial vaccination.

Twenty-four 10-month-old Polled Hereford heifers were inoculated sc with live cells of one of the following strains of Brucella abortus: S19 delta 31K (n = 4), S19 delta SOD (n = 4), RB51 (n = 4), and strain 19 (n = 6); controls (n = 6) were given saline solution. Heifers given the deletion mutants S19 delta 31K and S19 delta SOD, and those given strain 19 developed antibody responses to B abortus and cutaneous reactions to brucellin. Heifers given strain RB51 did not develop antibodies that reacted in the standard tube agglutination test, but sera reacted in tests, using an antibody dot-blot assay containing RB51 antigen. The S19 delta 31K and S19 delta SOD strains of B abortus isolated from lymph node tissue after vaccination did not differ genetically from the master stock strain. All heifers were bred naturally at 16 to 17 months of age, and were challenge-exposed intraconjunctivally with virulent B abortus strain 2308 during the fifth month of pregnancy. All vaccinated heifers were protected (ie, none aborted and none had B abortus isolated from their tissues after parturition). Calves born from vaccinated dams were free of B abortus. Antibody responses in heifers after challenge exposure were an indicator of immunity. All 5 control heifers (nonvaccinated) developed serum antibodies after challenge exposure; 3 aborted, and 1 delivered a small, weak calf at 8.5 months of gestation. Thus, live mutant strains of B abortus can induce protective immunity when given at 10 months of age, and strain RB51 is a strong candidate for further testing.

During the spring of the first year of a vaccine study, 57 of 238 calves (24%), in which modified-live Pasteurella haemolytica vaccine (MLV) was injected twice, developed 1 or more abscesses. Abscesses were not observed after multiple visual examinations of 437 calves given killed P. haemolytica bacterin or placebo injections of similar adjuvants used in the vaccine and bacterin. Calves that developed abscesses after the second injection of MLV weighed significantly (P < 0.05) less (on the basis of body weight adjusted for weaning weight) at the second injection than did those that did not develop abscesses. Compared with calves given MLV that did not develop observable abscesses, calves developing abscesses after the second injection of MLV weighed 11.0 and 14.2 kg less, respectively, at 56 days and 112 days after injection, and they had 11.0 kg less gain at 56 days after injection. Abscess prevalence tended to be highest on certain days or at certain locations used for cattle processing, and the prevalence of abscesses increased in cattle processed later on a given day. Abscesses were not observed in 2 other groups of similarly treated calves vaccinated in the autumn or in the subsequent spring.

A commercially available Salmonella bacterin was administered to Holstein calves starting at 1 to 19 weeks of age. Serum samples were obtained before administering bacterin and at 2-week intervals thereafter. An ELISA with Salmonella dublin lipopolysaccharide (LPS) or S dublin whole cells as antigen, was used to measure specific IgG and IgM responses. Antibody responses to LPS were not detected from calves < 12 weeks old inoculated with killed bacterin. Immunoglobulin responses to whole-cell antigen were detected from all age groups of calves inoculated with the same killed Salmonella bacterin. Calves < 11 weeks old are able to produce immunoglobulins to some whole-cell antigens, but are unable to produce anti-LPS immunoglobulins when inoculated with killed Salmonella bacterin. This age-related response to killed Salmonella antigens may account, in part, for increased susceptibility to salmonellosis in calves < 12 weeks old. In comparison to the response for killed antigen, 8 calves given modified-live aromatic-dependent S dublin bacterin at 1 to 3 weeks of age had detectable anti-LPS immunoglobulin after immunization, although the response was not as rapid and was of a lesser magnitude than that of older calves given killed Salmonella bacterin.

Live, avirulent Escherichia coli vaccine strains were constructed and tested for efficacy in preventing colibacillosis in 4-week-old pigs. Either or both of 2 plasmids were inserted into avirulent E coli strain G58-1 (0101:NM). These plasmids were pPMC4, which encodes for LTb subunits of heat-labile enterotoxin, and pDHF1, which encodes for K88ac fimbriae. Litter- and weight-matched pigs were removed from sows when they were 10 days old and vaccinated orally with the constructed strains or with G58-1 (negative control vaccine) when they were 2 weeks old and 5 days later. All pigs were challenge-inoculated with virulent E coli strain 3030-2 (0157:K88, LT+, STb+) 2 weeks after the first vaccination. Only 1 pig vaccinated with G58-1/pPMC4/pDHF1 developed diarrhea and none died following challenge inoculation. Seventeen of 31 control pigs developed diarrhea and 11 died. Of 18 pigs vaccinated with G58-1/pDHF1 then challenge-inoculated with the virulent strain, 5 developed diarrhea and 2 died. Fifteen of 18 litter- and weight-matched controls developed diarrhea and 8 died. When compared with G58-1 (negative control), G58-1/pPMC4 afforded no protection to pigs challenge-inoculated with 3030-2.