Immune Responses of Goats to Corynebacterium pseudotuberculosis and its Mycolic Acids (MAs) Extract

Abstract

Corynebacterium pseudotuberculosis is the causative agent of caseous lymphadenitis in small ruminants and is of considerable economic importance in many countries worldwide. The control of the disease in animals depends on the control of the disease in infected animals. Nevertheless, few countries where the disease was previously endemic have successfully eradicated the pathogen. This investigation was undertaken to determine the antibody titre (IgM and IgG) in does challenged with C. pseudotuberculosis and its Mycolic acids (MAs) immunogen extract. About 12 healthy crossbred female Boer goats were assigned into three groups (A, B and C), each comprising of 4 goats. Group A (Negative control group) was inoculated intradermally with 2 ml of sterile phosphate-buffered saline (PBS-pH 7); Group B (Mycolic acid group) was inoculated intradermally with 2 ml of immunogenic Mycolic acid extract (1g /ml); while group C (Positive control group) was inoculated intradermally with 2 ml of 10 9 colony-forming unit of live C. pseudotuberculosis. All the animals were observed for 90 days post-inoculation. Blood samples were collected via the jugular vein from all the groups before the inoculation and once weekly after the challenge until the end of the research period. The result of the study showed that the Immunoglobulin M (IgM) concentration in goats inoculated with C. pseudotuberculosis significantly (p<0.05) increased at week 2 (18.97±0.28 ng/ml), week 3 (33.97±0.59 ng/ml), week 4 (31.94±0.28 ng/ml) and week 5 (12.51±2.42). Whereas, in the mycolic acid group, the IgG antibody titre increased consistently from week 1 to week 3 (20.99±1.96 ng/ml; 15.52±3.78 ng/ml; 14.74±0.34 ng/ml) respectively. On the other hand, the Immunoglobulin G (IgG) concentration was found to significantly increase (p<0.05) after treatments and the increase persisted up till week 11 post-inoculation. The concentration of IgG steadily increased in C. pseudotuberculosis and MAs-treated groups, reaching the peak at week 9 (32.82±8.56 ng/ml) in C. pseudotuberculosis group and week 10 (28.41±1.27 ng/ml) in MAs group, then declined slowly from week 10 till week 12. In conclusion, there was an elevated level in the IgM and IgG antibodies post-infection with C. pseudotuberculosis and MAs. However, while the IgG antibody levels started declining at week 9 for C. pseudotuberculosis, the MAs group was sustained until week ten before reducing. Therefore, MAs can be used as an immunogen to control caseous lymphadenitis infection caused by C. pseudotuberculosis among small ruminants.