The chronic shedders identification is a critical issue for the control of Q fever in cattle, but at present none of the available immunological assays can discriminate the infection status. Following the example of the human protocols for the assessment of Q fever infection status, we evaluated two modified commercial kits for anti-C.burnetii phase I and II antibodies detection: ELISA and IgG/IgM IFAT.
Sera were collected in 4 dairy herds with confirmed Q fever. A total of 99 animals were sampled 3 times over 6 months and classified in 5 groups with routine serological tests and PCR: NI- (non infected, seronegative, not shedder, n=26); NI+ (non infected, seropositive, not shedder, n=29); CS (seropositive chronic shedder, n=12); OS+ (occasional seropositive shedder, n=20); OS- (occasional seronegative shedder, n=12).
All the 297 samples were tested with the modified ELISA kit and a selection of 107 samples was made for IFAT. The groups NI- and OS- were confirmed as negative, consequently only the groups NI+, CS e OS+ were considered for the evaluation.
Differences were observed among groups in ELISA, permitting to discriminate CS (more relevant from an epidemiological point of view) from NI+ and OS+. Overall, NI+ showed significantly lower S/P values with respect to CS and OS+. Considering the interaction between group and phase, in OS+ the S/P values of phase I resulted significantly higher than S/P values of phase II.
All the ELISA positive samples were confirmed in IgG IFAT and only 5 samples were IgM positive. The IgG IFAT highlighted that NI+ had significantly lower titers than CS; OS showed no significant differences, with halfway values between NI+ and CS. All groups had phase I > phase II titers.
The ELISA seems to perform better as tool for the chronic status identification, showing significant differences among groups.