Location: Food and Feed Safety Research
Title: Development of challenge models to evaluate the efficacy of a vaccine to reduce carriage of Salmonella in peripheral lymph nodes of cattle Authors
|Loneragan, Guy -|
|Farrow, Russel -|
|Krueger, Nathan -|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2013
Publication Date: July 10, 2013
Citation: Edrington, T.S., Loneragan, G.H., Hill, J.E., Genovese, K.J., Brichta-Harhay, D.M., Farrow, R.L., Krueger, N.A., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2013. Development of challenge models to evaluate the efficacy of a vaccine to reduce carriage of Salmonella in peripheral lymph nodes of cattle. Journal of Food Protection. 76:1259-1263. Interpretive Summary: Cattle may contain Salmonella, a bacteria that can make people sick. Peripheral lymph nodes in these cattle may contain Salmonella that are not eliminated by interventions in the slaughter plant. Vaccines are currently being evaluated for controlling Salmonella in cattle, and this research was conducted to specifically evaluate if vaccines would prevent uptake of Salmonella by the peripheral lymph nodes following oral challenge. Results indicate that these lymph nodes can become infected with Salmonella following oral inoculation and a benefit of the vaccine as a preventative was observed. Prior to expensive live animal field studies, our experimental model may be used to pre-screen other likely intervention strategies.
Technical Abstract: Recent research suggests that peripheral lymph nodes in cattle may be a significant source of Salmonella contaminating ground beef. The objective of this research was to determine whether a commercially-available Salmonella vaccine protects calves from lymph node colonization following significant oral challenge with two strains of Salmonella frequently isolated from cattle, Salmonella Newport and Montevideo. Three experiments were conducted in which weaned calves were randomly assigned to treatment (Control or Vaccinated) and within each treatment inoculated with either Salmonella Montevideo or Newport (8 head/treatment and each strain; 32 total). Vaccinate calves were administered a commercially-available Salmonella Newport SRP vaccine (2 ml s.c.) while control calves received a sham-injection of corn oil (2 ml s.c.). A second booster vaccination and sham-injections were administered on d 21. All calves were inoculated with their respective Salmonella strain 14 d following the booster vaccination. Calves were euthanized 14, 28, 35, and 42 days post-inoculation, and various peripheral lymph nodes were collected for Salmonella culture (quantitative and qualitative). Fecal samples were collected throughout the experiments. In the first experiment, the oral challenge was successful in infecting peripheral lymph nodes with both strains of Salmonella. Few treatment differences were observed; however, at 21 d post-inoculation, Salmonella Newport-challenged calves treated with the vaccine had fewer (P < 0.05) right popliteal (0 versus 75%) and right pre-scapular nodes (0 versus 75%) that were Salmonella-positive compared to Control calves. The percentage of Salmonella-positive left popliteal and left pre-scapular nodes likewise tended (P = 0.10) to decrease in the Vaccine treatment compared to non-vaccinated controls (Newport-challenged calves only). Experiment II utilized a lower challenge dose (10**7) than Experiments I and III (10**10), and following two necropsies (14 and 28 d post-challenge), only one peripheral lymph node was Salmonella-positive, and the study terminated. Experiment III utilized the higher challenge dose and examined a longer duration between challenge and necropsy. Results were similar to the first experiment in that a higher challenge dose was successful in producing Salmonella-positive peripheral lymph nodes with each of the two challenge strains. No significant treatment differences were observed in the Montevideo- or Newport-challenged calves, although there was a trend (P = 0.13) for fewer Salmonella-positive right sub-iliac nodes in the vaccine treatment. When analyzed by day of necropsy, the percentage of left axillary nodes was significantly reduced (100 versus 0% for the control and vaccine treatments, respectively) by the vaccine treatment (28 d post-challenge). Serogrouping the isolates recovered from the lymph nodes confirmed recovery of the challenge strains of Salmonella. Herein, we are the first to document the uptake of Salmonella by the peripheral lymph nodes in cattle following significant oral challenge and provide a model for evaluating potential intervention strategies. While few significant treatment effects were observed, the trends observed in the vaccinated calves challenged with Salmonella Newport suggests a potential benefit and warrants further research.