Poster
Evaluation of antibody responses to commercial Mannheimia haemolytica vaccines in calves using whole-organism and leukotoxin-specific ELISAs
| Date/Time: |
8/27/2026
|
| Author: |
Korakrit Poonsuk |
| Clinic: |
Washington State University |
| City, State, ZIP: |
Pullman, WA 99164 |
K. Poonsuk, DVM, MSc, PhD, DACVM
1
;
B. Terhaar, DVM
2
;
1Washington Animal Disease Diagnostic Laboratory, Washington State University, Pullman, WA, 99163
2US Beef Business, Elanco Animal health, Winterset, IA, 50273
Introduction:
Mannheimia haemolytica (MH) is a major bacterial pathogen associated with bovine respiratory disease, and vaccination is a cornerstone of prevention. Commercial vaccines, including Nuplura PH, One Shot, and Presponse SQ, are designed to stimulate protective immunity against key bacterial antigens, including surface components and/or leukotoxin (LKT), an important virulence factor. However, interpretation of serologic responses in young calves may be influenced by maternally derived antibodies. The objective of this study was to evaluate antibody responses following vaccination using complementary serologic assays and to assess the impact of baseline immunity against the bacterial surface components and/or leukotoxin on detection of vaccine-induced responses.
Materials and methods:
Calves were stratified into two groups based on baseline antibody levels: low baseline (Group 1) and high baseline (Group 2), with the latter corresponding to younger calves (10–45 days old) and consistent with maternally derived antibodies. Calves were vaccinated with Nuplura PH, One Shot, or Presponse SQ and managed under similar conditions throughout the study period. Serum samples were collected on the day of vaccination (Day 1) and approximately 28 days following vaccination (Day 28). Samples were tested using two serologic assays. A MH whole-organism (WO) ELISA was used to detect antibodies against a broad range of surface antigens, and a leukotoxin (LKT) ELISA was used to detect antibodies targeting the LKT antigen. Optical density (OD) values were measured under standardized assay conditions.
For each animal, changes in antibody levels were calculated as ΔOD (Day 28 – Day 1). Descriptive comparisons of ΔOD values were performed within and between groups to evaluate patterns of antibody response following vaccination. Responses detected by WO and LKT ELISAs were compared to assess differences in antigen-specific immune profiles and the influence of baseline antibody levels on detection of vaccine-induced responses.
Results:
Calves with low baseline antibody levels demonstrated clear serologic responses following vaccination. In this group, calves vaccinated with Nuplura PH and One Shot showed consistent increases in WO ELISA values across post-vaccination timepoints, with several animals exhibiting marked increases relative to pre-vaccination levels. Corresponding increases in LKT ELISA values were also observed in these groups, although the magnitude of response was lower compared to WO ELISA.
In calves with high baseline antibody levels, WO and LKT ELISA values declined over time across all vaccine groups. This decline was observed from D1 to D28 and which consistent with decreasing baseline antibody levels. Under these conditions, increases in antibody responses following vaccination were not clearly detectable in either assay. In this group, calves vaccinated with Presponse SQ showed minimal to no increase in LKT ELISA values. Among calves vaccinated with Nuplura PH and One Shot, WO ELISA values remained higher overall compared to LKT ELISA values. Across all animals in these groups, WO ELISA consistently detected higher antibody levels and more frequent increases following vaccination, whereas LKT ELISA detected more limited and variable responses depending on vaccine group and baseline antibody status.
Significance:
Commercial Mannheimia haemolytica vaccines containing surface antigens and/or leukotoxin (LKT), including Nuplura PH, One Shot, and Presponse SQ, induced detectable immune responses in calves. Antibody responses to both antigen types were observed in the Nuplura PH and One Shot vaccinated groups, whereas anti-LKT responses were less prominent in calves vaccinated with Presponse SQ. Overall, responses against surface antigens were consistently stronger and more readily detected than those targeting LKT.
In calves with high baseline antibodies, presumed to reflect maternally derived immunity, vaccine-induced responses were less detectable. This effect was most evident in younger calves, where responses to LKT were particularly limited. Under these conditions, multicomponent vaccines still provided more consistent evidence of immune stimulation through detectable responses to surface antigens.
These findings support the efficacy of multicomponent M. haemolytica vaccines in stimulating broad humoral responses and highlight the importance of considering baseline immunity when evaluating vaccine performance. Complementary use of whole-organism (WO) and LKT ELISAs provides a more complete assessment of vaccine-induced immunity, particularly in young calves with high maternal antibody levels.
