Background: Canine monocytic ehrlichiosis (CME) is a tick-borne disease with a global distribution, caused by Ehrlichia canis. The inflammatory response to E. canis infection includes changes in certain acute phase proteins (APP) and in biomarkers of the oxidative status. APP responses are considered part of the innate immune response to CME. The aim of this study was to evaluate the APP and oxidative marker responses in dogs vaccinated against CME with an attenuated vaccine and subsequently challenged with a wild E. canis strain.
Methods: The study included 3 groups of 4 beagle dogs. Group 1 dogs were inoculated subcutaneously with an attenuated E. canis vaccine on day 0, and again on day 213. Group 2 initially served as controls for group 1 during the vaccination phase and then vaccinated once on day 213. Group 3 consisted of naïve dogs which constituted the control group for the challenge phase. All 12 dogs were infected intravenously with a wild strain of E. canis on day 428 of the study. APP levels were serially measured during two periods: days 0-38 post-vaccination (groups 1 and 2) and days 0-39 post-challenge (groups 1, 2, 3).
Results: Changes in C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin, albumin, paraoxonase-1 (PON-1) and total antioxidant capacity (TAC) were of significantly smaller magnitude in vaccinated dogs and appeared later on a time scale compared to unvaccinated dogs challenged with a wild strain. Alterations in the level of APP during the vaccination phase of the study were of lower extent compared to those in the challenged unvaccinated dogs during the post-challenge phase. Positive APP levels correlated positively with the rickettsial load, body temperature and negatively with the thrombocyte counts (p < 0.05).
Conclusions: Vaccination with an attenuated E. canis strain and challenge with a wild strain resulted in considerably reduced responses of positive and negative APP, and oxidative biomarker responses in vaccinated compared to unvaccinated dogs, reflecting a milder innate inflammatory response conferred by protection of the vaccine.