Bayesian latent class estimation of sensitivity and specificity parameters of the PMS-PCR test for the diagnosis of cattle sub-clinically infected with Mycobacterium avium subsp. paratuberculosis
2020
Verdugo, Cristobal | Cardemil, Carla | Steuer, Pamela | Salgado, Miguel
The objective of this study was to estimate the performance of the peptide magnetic separation PCR test (PMS-PCR) for the diagnosis of Mycobacterium avium subsp. paratuberculosis (MAP) in sub-clinically infected dairy cattle. Twenty-one herds were randomly selected from a source population of 131 commercial dairy herds with a known history of MAP infection, located in the De Los Rios and De Los Lagos regions, in southern Chile. In the selected herds, all milking cows with ≥2 parities and without any clinical signs were sampled, collecting feces and blood-serum samples. The PMS-PCR test was used to analyze the fecal samples, while serum samples were analyzed using a commercial ELISA kit. A Bayesian latent class model was used to estimate the sensitivity (Se) and specificity (Sp) of the diagnostic tests.A total of 1381 animals were sampled in the 21 selected dairy herds, with an average sample size of 65 animals per herd (range 10–721). The PMS-PCR test had a greater Se than the ELISA test, with a median of 85.5 % (posterior probability interval (PPI) 95 %: 79.3–91.0%), while the ELISA test presented a median of 21.7 % (95 % PPI: 18.3–25.4%). On the other hand, the ELISA test had a better Sp than the PMS-PCR test, with a median of 97.7 % (95 % PPI: 96.6–98.5%), whereas PMS-PCR presented a median of 90.8 % (95 % PPI: 88.3–93.9%). Model results showed that PMS-PCR has a better Se than all available tests for MAP diagnosis in subclinical animals. However, this test should be used with care in herds with high infection rates, where a high MAP environmental load is expected, potentially increasing the frequency of false positive cases due to the pass-through phenomenon.
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