Levels of Ovo-transferrin concentrations in layer chickens experimentally infected with wild-type or small-colony variants of Streptococcus equi subsp. zooepidemicus via different routes

Abstract

Ovo-transferrin is a positive acute-phase protein in chickens, and a possible biomarker of inflammation and infection. To investigate the level of serum-OvoTransFerrin (OTF) during infectious disease we characterized the OTF levels in brown layer chickens inoculated with a wild-type (WT) or a small-colony-variant (SCV) of Streptococcus equi subsp. zooepidemicus via the intravenous (IV) or intra-tracheal (IT) routes. Four experimental groups were formed; WT-IV, SCV-IV, WT-IT and SCV-IT each containing 11 birds. From each group, two birds were euthanized on day 1 and day 3 post-inoculation (p.i.), respectively, and remaining birds were euthanized on day 14 p.i. Two hypotheses were tested: 1. OTF levels in inoculated birds were above the day 0 and/or the negative-control bird concentrations, independent on strain and inoculation route. 2. OTF levels varied according to the bacterial phenotype and route of inoculation. The OTF concentration was measured by a commercial Chicken-OTF. ELISA. The median of OTF concentrations (mg/ml) was increased at day 14 p.i. in WT-IV (median = 5.7, range = 4.4 to 7.0), WT-IT (5.3, 3.1 to 7.6) and SCV-IV (6.5, 5.8 to 6.7) groups when compared to corresponding day 0 concentrations (3.0, 2.0 to 3.6; 2.5 1.8 to 3.6 and 2.1, 0.8 to 2.9 mg/ml, respectively) (P=0.01). In the WT-IV group, the median concentration at day 14 p.i. was higher than the corresponding control (2.9, 2.3 to 11 mg/mi) (P=0.05). In the SCV-IT, there was an insignificant difference between the medians of day 0 and day 14 p.i., however, two birds in the group had the highest OTF concentrations - one at day 1 (9 mg/ml) and another at day 14 p.i. (10 mg/mi). There were no significant differences in the median OTF concentrations when comparing between the experimental groups. The results indicate that the OTF response in layer chickens reflects the inflammatory state. However, the OTF level did not evolve in a strain and/or inoculation route dependent manner.