Abstract
Bovine paratuberculosis (PTB) is a chronic granulomatous enteritis, caused by Mycobacterium avium subsp. paratuberculosis (MAP), responsible for important economic losses in the dairy industry. Current diagnostic methods have low sensitivities for detection of latent forms of MAP infection, defined by focal granulomatous lesions and scarce humoral response or MAP presence. In contrast, patent infections correspond to multifocal and diffuse types of enteritis where there is increased antibody production, and substantial mycobacterial load. Our previous RNA-Seq analysis allowed the selection of five candidate biomarkers overexpressed in peripheral blood of MAP infected Holstein cows with focal (ABCA13 and MMP8) and diffuse (FAM84A, SPARC and DES) lesions vs. control animals with no detectable PTB-associated lesions in intestine and regional lymph nodes. The aim of the current study was to assess the PTB diagnostic potential of commercial ELISAs designed for the specific detection of these biomarkers. The ability of these ELISAs to identify animals with latent and/or patent forms of MAP infection was investigated using serum from naturally infected cattle (n = 88) and non-infected control animals (n = 67). ROC analysis revealed that the ABCA13-based ELISA showed the highest diagnostic accuracy for the detection of infected animals with focal lesions (AUC 0.837, sensitivity 79.25% and specificity 88.06%) and with any type of histological lesion (AUC 0.793, sensitivity 69.41% and specificity 86.57%) improving on the diagnostic performance of the popular IDEXX ELISA and other conventional diagnostic methods. SPARC and MMP8 showed the highest diagnostic accuracy for the detection of animals with multifocal (AUC 0.852) and diffuse lesions (AUC 0.831), respectively. In conclusion, our results suggest that quantification of ABCA13, SPARC and MMP8 by ELISA has the potential for implementation as a diagnostic tool to reliably identify MAP infection, greatly improving early detection of MAP latent infections when antibody responses and fecal shedding are undetectable using conventional diagnostic methods.
Highlights
Bovine paratuberculosis (PTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), that is responsible for important economic losses due to reduced milk production, premature culling, reduced slaughter value and continued spread of infection [1, 2]
The control of PTB at the herd level is based mainly on the identification and withdrawal of infected animals, especially MAP-shedding animals, to suppress sources of infection and maximize the productive life of the animals [45]. The effectiveness of these control programs is strongly conditioned by the diagnostic methods used for the detection of infected animals
Our results indicate that the ABCA13, SPARC and MMP8-based Enzyme-linked immunosorbent assay (ELISA) have higher AUC values and sensitivities than the IDEXX ELISA and other current diagnostic methods for detection of animals with focal, multifocal and any type of histopathological lesions, respectively
Summary
Bovine paratuberculosis (PTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), that is responsible for important economic losses due to reduced milk production, premature culling, reduced slaughter value and continued spread of infection [1, 2]. Two forms of infection, latent or patent, can be distinguished in MAP infected cattle [12]. The disease typically progresses from a latent form with low or moderate frequency of microbiological or humoral immunological evidence of infection, characterized by the presence of focal histological lesions in their intestinal tissues to more severe forms of the disease with a high frequency of microbiological or humoral immunological evidence of infection, in which the granulomatous lesions are patent (multifocal and diffuse lesions readily detected upon microscopic examination of the intestine and associated lymph nodes). A latent form would represent a form of silent PTB that causes no direct losses, but that maintains a hidden MAP reservoir in a herd, while a patent form often corresponds with a visibly clinical disease
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