Degree Final Project defended by Jaime Ricón Fernández de la Puente

June 20^th, 2023

Goat tuberculosis (TB) is a disease with a significant economic and health impact, subject to control and eradication programs in some areas of the Spanish territory, which employ diagnostic tests such as single or comparative intradermal tuberculin (SIT and CIT respectively) tests) and occasionally, the interferon-gamma test (IGRA). These plans are based on the detection and slaughter of positive animals; however, diagnostic tests have limitations, and new techniques have been sought to increase their specificity (Sp) and sensitivity (Se). One of these techniques is the P22 ELISA, a humoral-based test that can be applied to different samples such as serum and milk. This technique has been used in conjunction with the intradermal tuberculin test (SIT/CIT) (booster effect or potentiation of the immune response) to increase the detection of infected animals, with both serum and milk samples. However, little information is available on whether this booster strategy might decrease Sp in TB free herds. The objective of this study was to evaluate the effect of recent SIT/CIT on the results of the P22 ELISA in serum and milk samples taken from a TB-free goat herd. These samples were collected from 113 animals on day 0, and subsequently on days 15, 30, and 60 after the SIT/CIT. All samples were analyzed using the P22 ELISA. On day 0, none of the study animals (n=113) tested positive for SIT, CIT, or IGRA, and only one animal (0.8%) tested positive for P22 ELISA in milk and serum samples, yielding a Sp of 99.1% (95% CI 95.2-99.8). The number of positive animals by P22 ELISA significantly (p=0.003) increased to 13 [Sp of 88.5% (95% CI 81.3-93.2)] in serum samples on day 15, being the number of reactors (p<0.001) and %ELISA values significantly (p=0.002) higher in serum than in milk. A smaller decrease in Sp was observed in milk samples compared to serum. According to the results of this study, this diagnostic strategy may imply a significant loss of Sp in the P22 ELISA in the first weeks after the skin test when used in TB-free herds, especially when using serum samples. It would be necessary to confirm these results in a larger number of herds to consider them for the design of future programs for the eradication of goat TB