Abstract
Histophilosis, a mucosal and septicemic infection of cattle is caused by the Gram negative pathogen Histophilus somni (H. somni). As existing vaccines against H. somni infection have shown to be of limited efficacy, we used a reverse vaccinology approach to identify new vaccine candidates. Three groups (B, C, D) of cattle were immunized with subunit vaccines and a control group (group A) was vaccinated with adjuvant alone. All four groups were challenged with H. somni. The results demonstrate that there was no significant difference in clinical signs, joint lesions, weight change or rectal temperature between any of the vaccinated groups (B,C,D) vs the control group A. However, the trend to protection was greatest for group C vaccinates. The group C vaccine was a pool of six recombinant proteins. Serum antibody responses determined using ELISA showed significantly higher titers for group C, with P values ranging from < 0.0148 to < 0.0002, than group A. Even though serum antibody titers in group B (5 out of 6 antigens) and group D were significantly higher compared to group A, they exerted less of a trend towards protection. In conclusion, the vaccine used in group C exhibits a trend towards protective immunity in cattle and would be a good candidate for further analysis to determine which proteins were responsible for the trend towards protection.
Highlights
Histophilus somni, previously known as Haemophilus somnus, is an economically important pathogen that affects the cattle industry by causing a variety of mucosal and systemic infections [1,2,3,4,5], including septicemia, respiratory disease, reproductive tract disorders, pericarditis, PLOS ONE | DOI:10.1371/journal.pone.0159070 August 8, 2016Antibody Responses in Cattle to Histophilus somni Subunit Vaccines roles of these authors are articulated in the 'author contributions' section
Serum antibodies against H. somni antigens were determined using an Enzyme-Linked Immunosorbent Assay (ELISA) procedure with individual serum samples taken prior to vaccination, at the time of boost, immediately prior to H. somni challenge, and immediately prior to euthanization
Statistical determination of serum antibodies against H. somni antigens in group B or group C or group D for 21 days post challenge compared to serum antibodies in the non vaccinated group A was statistically significant at P < 0.05 using Mann Whitney test in a two tailed P value, except for antigen R18 in group B
Summary
Histophilus somni, previously known as Haemophilus somnus, is an economically important pathogen that affects the cattle industry by causing a variety of mucosal and systemic infections [1,2,3,4,5], including septicemia, respiratory disease, reproductive tract disorders, pericarditis, PLOS ONE | DOI:10.1371/journal.pone.0159070 August 8, 2016Antibody Responses in Cattle to Histophilus somni Subunit Vaccines roles of these authors are articulated in the 'author contributions' section.
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